Table of Contents

Introduction

Apache Camel is a powerful Spring based Integration Framework.

Camel implements the Enterprise Integration Patterns allowing you to configure routing and mediation rules in either a Java based Domain Specific Language (or Fluent API) or via Spring based Xml Configuration files. Either approaches mean you get smart completion of routing rules in your IDE whether in your Java or XML editor.

Apache Camel uses URIs so that it can easily work directly with any kind of Transport or messaging model such as HTTP, ActiveMQ, JMS, JBI, SCA, MINA or CXF Bus API together with working with pluggable Data Format options. Apache Camel is a small library which has minimal dependencies for easy embedding in any Java application.

Apache Camel can be used as a routing and mediation engine for the following projects:

So don't get the hump, try Camel today!

Getting Started with Apache Camel

The Enterprise Integration Patterns (EIP) book

The purpose of a "patterns" book is not to advocate new techniques that the authors have invented, but rather to document existing best practices within a particular field. By doing this, the authors of a patterns book hope to spread knowledge of best practices and promote a vocabulary for discussing architectural designs.
One of the most famous patterns books is
Design Patterns: Elements of Reusable Object-oriented Software by Erich Gamma, Richard Helm, Ralph Johnson and John Vlissides. Some people refer to this as the "gang of four" book, partly to distinguish this book from other books that use "Design Patterns" in their titles and, perhaps, partly because they cannot remember the names of all four authors.
Since the publication of Design Patterns, many other patterns books, of varying quality, have been written. One famous patterns book is called Enterprise Integration Patterns: Designing, Building, and Deploying Messaging Solutions by Gregor Hohpe and Bobby Woolfe. It is common for people to refer to this book as EIP, which is an acronym of its title. As the subtitle of EIP suggests, the book focusses on design patterns for asynchronous messaging systems. The book discusses 65 patterns. Each pattern is given a textual name and most are also given a graphical symbol. The graphical symbols are intended to be used in architectural diagrams.

The Camel project

Camel (http://activemq.apache.org/camel/) is an open-source, Java-based project that is a part of the Apache ActiveMQ project. Camel provides a class library that, according to its documentation, can be used to implement 31 design patterns in the EIP book. I am not sure why the Camel documentation discusses only 31 of the 65 EIP design patterns. Perhaps this is due to incomplete documentation. Or perhaps it means that the Camel project, which is less than 1 year old at the time of writing, is not yet as feature rich as the EIP book.
Because Camel implements many of the design patterns in the EIP book, it would be a good idea for people who work with Camel to read the EIP book.

Online documentation for Camel

The Camel project was started in early 2007. At the time of writing, the Camel project is too young for there to be published books available on how to use Camel. Instead, the only source of documentation seems to the documentation page on the Apache Camel website.

Problems with Camel's online documentation

Currently, the online documentation for the Apache Camel project suffers from two problems. First, the documentation is incomplete. Second, there is no clearly specified reading order to the documentation. For example, there is no table of contents. Instead, documentation is fragmented over a collection of 60+ web pages, and hypertext links haphazardly tie these web pages to each other. This documentation might suffice as reference material for people already familiar with Camel but it does not qualify as a tutorial for beginners.
The problems with the documentation are unlikely to be due to, say, its author(s) lacking writing ability. Rather, it is more likely that the problems are due to the author(s) lack of time. I expect Camel's documentation will improve over time. I am writing this overview of Camel to partially counter some of the problems that currently afflict the Camel documentation. In particular, this document aims to serve as a (so far, incomplete) "beginner's guide to Camel". As such, this document tries to complement, rather than compete with, the online Camel documentation.

A useful tip for navigating the online documentation

There is one useful hint I can provide for reading the online Camel documentation. Each documentation page has a logo at the top, and immediately underneath this is a think reddish bar that contains some hypertext links. The Hypertext links on left side of this reddish bar indicate your position in documentation. For example, If you are on the "Languages" documentation page then the left-hand side of the reddish bar contains the following links.

As you might expect, clicking on "Apache Camel" takes you back to the home page of the Apache Camel project, and clicking on "Documentation" takes you to the main documentation page. You can interpret the "Architeture" and "Languages" buttons as indicating you are in the "Languages" section of the "Architecture" chapter. Doing this gives you at least some sense of where you are within the documentation. If you are patient then you can spend a few hours clicking on all the hypertext links you can find in the documentation pages, bookmark each page with a hierarchical name (for example, you might bookmark the above page with the name "Camel Ð Arch Ð Languages") and then you can use your bookmarks to serve as a primitive table of contents for the online Camel documentation.

Online Javadoc documentation

The Apache Camel website provides Javadoc documentation. It is important to note that the Javadoc documentation is spread over several independent Javadoc hierarchies rather than being all contained in a single Javadoc hierarchy. In particular, there is one Javadoc hierarchy for the core APIs of Camel, and a separate Javadoc hierarchy for each communications technology supported by Camel. For example, if you will be using Camel with ActiveMQ and FTP then you need to look at the Javadoc hierarchies for the core API, ActiveMQ API and FTP API.

Concepts and terminology fundamental to Camel

I said in Section 3.1 ("Problems with Camel's online documentation") that the online Camel documentation does not provide a tutorial for beginners. Because of this, in this section I try to explain some of the concepts and terminology that are fundamental to Camel. This section is not a complete Camel tutorial, but it is a first step in that direction.

Endpoint

The term endpoint is often used when talking about inter-process communication. For example, in client-server communication, the client is one endpoint and the server is the other endpoint. Depending on the context, an endpoint might refer to an address, such as a host:port pair for TCP-based communication, or it might refer to a software entity that is contactable at that address. For example, if somebody uses "www.example.com:80" as an example of an endpoint, they might be referring to the actual port at that host name (that is, an address), or they might be referring to the web server (that is, software contactable at that address). Often, the distinction between the address and software contactable at that address is not an important one.
Some middleware technologies make it possible for several software entities to be contactable at the same physical address. For example, CORBA is an object-oriented, remote-procedure-call (RPC) middleware standard. If a CORBA server process contains several objects then a client can communicate with any of these objects at the same physical address (host:port), but a client communicates with a particular object via that object's logical address (called an IOR in CORBA terminology), which consists of the physical address (host:port) plus an id that uniquely identifies the object within its server process. (An IOR contains some additional information that is not relevant to this present discussion.) When talking about CORBA, some people may use the term "endpoint" to refer to a CORBA server's physical address, while other people may use the term to refer to the logical address of a single CORBA object, and other people still might use the term to refer to any of the following:

CamelContext

A CamelContext object represents the Camel runtime system. You typically have one CamelContext object in an application. A typical application executes the following steps.

  1. Create a CamelContext object.
  2. Add endpoints Ð and possibly Components, which are discussed in Section 4.5 ("Components") Ð to the CamelContext object.
  3. Add routes to the CamelContext object to connect the endpoints.
  4. Invoke the start() operation on the CamelContext object. This starts Camel-internal threads that are used to process the sending, receiving and processing of messages in the endpoints.
  5. Eventually invoke the stop() operation on the CamelContext object. Doing this gracefully stops all the endpoints and Camel-internal threads.
    Note that the CamelContext.start() operation does not block indefinitely. Rather, it starts threads internal to each Component and Endpoint and then start() returns. Conversely, CamelContext.stop() waits for all the threads internal to each Endpoint and Component to terminate and then stop() returns.
    If you neglect to call CamelContext.start() in your application then messages will not be processed because internal threads will not have been created.
    If you neglect to call CamelContext.stop() before terminating your application then the application may terminate in an inconsistent state. If you neglect to call CamelContext.stop() in a JUnit test then the test may fail due to messages not having had a chance to be fully processed.

CamelTemplate

Camel used to have a class called CamelClient, but this was renamed to be CamelTemplate to be similar to a naming convention used in some other open-source projects, such as the TransactionTemplate and JmsTemplate classes in Spring.
The CamelTemplate class is a thin wrapper around the CamelContext class. It has methods that send a Message or Exchange Ð both discussed in Section 4.6 ("Message and Exchange")) Ð to an Endpoint Ð discussed in Section 4.1 ("Endpoint"). This provides a way to enter messages into source endpoints, so that the messages will move along routes Ð discussed in Section 4.8 ("Routes, RouteBuilders and Java DSL") Ð to destination endpoints.

The Meaning of URL, URI, URN and IRI

Some Camel methods take a parameter that is a URI string. Many people know that a URI is "something like a URL" but do not properly understand the relationship between URI and URL, or indeed its relationship with other acronyms such as IRI and URN.
Most people are familiar with URLs (uniform resource locators), such as "http://...", "ftp://...", "mailto:...". Put simply, a URL specifies the location of a resource.
A URI (uniform resource identifier) is a URL or a URN. So, to fully understand what URI means, you need to first understand what is a URN.
URN is an acronym for uniform resource name. There are may "unique identifier" schemes in the world, for example, ISBNs (globally unique for books), social security numbers (unique within a country), customer numbers (unique within a company's customers database) and telephone numbers. Each "unique identifier" scheme has its own notation. A URN is a wrapper for different "unique identifier" schemes. The syntax of a URN is "urn:<scheme-name>:<unique-identifier>". A URN uniquely identifies a resource, such as a book, person or piece of equipment. By itself, a URN does not specify the location of the resource. Instead, it is assumed that a registry provides a mapping from a resource's URN to its location. The URN specification does not state what form a registry takes, but it might be a database, a server application, a wall chart or anything else that is convenient. Some hypothetical examples of URNs are "urn:employee:08765245", "urn:customer:uk:3458:hul8" and "urn:foo:0000-0000-9E59-0000-5E-2". The <scheme-name> ("employee", "customer" and "foo" in these examples) part of a URN implicitly defines how to parse and interpret the <unique-identifier> that follows it. An arbitrary URN is meaningless unless: (1) you know the semantics implied by the <scheme-name>, and (2) you have access to the registry appropriate for the <scheme-name>. A registry does not have to be public or globally accessible. For example, "urn:employee:08765245" might be meaningful only within a specific company.
To date, URNs are not (yet) as popular as URLs. For this reason, URI is widely misused as a synonym for URL.
IRI is an acronym for internationalized resource identifier. An IRI is simply an internationalized version of a URI. In particular, a URI can contain letters and digits in the US-ASCII character set, while a IRI can contain those same letters and digits, and also European accented characters, Greek letters, Chinese ideograms and so on.

Components

Component is confusing terminology; EndpointFactory would have been more appropriate because a Component is a factory for creating Endpoint instances. For example, if a Camel-based application uses several JMS queues then the application will create one instance of the JmsComponent class (which implements the Component interface), and then the application invokes the createEndpoint() operation on this JmsComponent object several times. Each invocation of JmsComponent.createEndpoint() creates an instance of the JmsEndpoint class (which implements the Endpoint interface). Actually, application-level code does not invoke Component.createEndpoint() directly. Instead, application-level code normally invokes CamelContext.getEndpoint(); internally, the CamelContext object finds the desired Component object (as I will discuss shortly) and then invokes createEndpoint() on it.
Consider the following code.

The parameter to getEndpoint() is a URI. The URI prefix (that is, the part before ":") specifies the name of a component. Internally, the CamelContext object maintains a mapping from names of components to Component objects. For the URI given in the above example, the CamelContext object would probably map the pop3 prefix to an instance of the MailComponent class. Then the CamelContext object invokes createEndpoint("pop3://john.smith@mailserv.example.com?password=myPassword") on that MailComponent object. The createEndpoint() operation splits the URI into its component parts and uses these parts to create and configure an Endpoint object.
In the previous paragraph, I mentioned that a CamelContext object maintains a mapping from component names to Component objects. This raises the question of how this map is populated with named Component objects. There are two ways of populating the map. The first way is for application-level code to invoke CamelContext.addComponent(String componentName, Component component). The example below shows a single MailComponent object being registered in the map under 3 different names.

The second (and preferred) way to populate the map of named Component objects in the CamelContext object is to let the CamelContext object perform lazy initialization. This approach relies on developers following a convention when they write a class that implements the Component interface. I illustrate the convention by an example. Let's assume you write a class called com.example.myproject.FooComponent and you want Camel to automatically recognize this by the name "foo". To do this, you have to write a properties file called "META-INF/services/org/apache/camel/component/foo" (without a ".properties" file extension) that has a single entry in it called class, the value of which is the fully-scoped name of your class. This is shown below.

If you want Camel to also recognize the class by the name "bar" then you write another properties file in the same directory called "bar" that has the same contents. Once you have written the properties file(s), you create a jar file that contains the com.example.myproject.FooComponent class and the properties file(s), and you add this jar file to your CLASSPATH. Then, when application-level code invokes createEndpoint("foo:...") on a CamelContext object, Camel will find the "foo"" properties file on the CLASSPATH, get the value of the class property from that properties file, and use reflection APIs to create an instance of the specified class.
As I said in
Section 4.1 ("Endpoint"), Camel provides out-of-the-box support for numerous communication technologies. The out-of-the-box support consists of classes that implement the Component interface plus properties files that enable a CamelContext object to populate its map of named Component objects.
Earlier in this section I gave the following example of calling CamelContext.getEndpoint().

myCamelContext.getEndpoint("pop3://john.smith@mailserv.example.com?password=myPassword");

When I originally gave that example, I said that the parameter to getEndpoint() was a URI. I said that because the online Camel documentation and the Camel source code both claim the parameter is a URI. In reality, the parameter is restricted to being a URL. This is because when Camel extracts the component name from the parameter, it looks for the first ":", which is a simplistic algorithm. To understand why, recall from Section 4.4 ("The Meaning of URL, URI, URN and IRI") that a URI can be a URL or a URN. Now consider the following calls to getEndpoint.

myCamelContext.getEndpoint("pop3:...");
myCamelContext.getEndpoint("jms:...");
myCamelContext.getEndpoint("urn:foo:...");
myCamelContext.getEndpoint("urn:bar:...");

Camel identifies the components in the above example as "pop3", "jms", "urn" and "urn". It would be more useful if the latter components were identified as "urn:foo" and "urn:bar" or, alternatively, as "foo" and "bar" (that is, by skipping over the "urn:" prefix). So, in practice you must identify an endpoint with a URL (a string of the form "<scheme>:...") rather than with a URN (a string of the form "urn:<scheme>:..."). This lack of proper support for URNs means the you should consider the parameter to getEndpoint() as being a URL rather than (as claimed) a URI.

Message and Exchange

The Message interface provides an abstraction for a single message, such as a request, reply or exception message.
There are concrete classes that implement the Message interface for each Camel-supported communications technology. For example, the JmsMessage class provides a JMS-specific implementation of the Message interface. The public API of the Message interface provides get- and set-style methods to access the message id, body and individual header fields of a messge.
The Exchange interface provides an abstraction for an exchange of messages, that is, a request message and its corresponding reply or exception message. In Camel terminology, the request, reply and exception messages are called in, out and fault messages.
There are concrete classes that implement the Exchange interface for each Camel-supported communications technology. For example, the JmsExchange class provides a JMS-specific implementation of the Exchange interface. The public API of the Exchange interface is quite limited. This is intentional, and it is expected that each class that implements this interface will provide its own technology-specific operations.
Application-level programmers rarely access the Exchange interface (or classes that implement it) directly. However, many classes in Camel are generic types that are instantiated on (a class that implements) Exchange. Because of this, the Exchange interface appears a lot in the generic signatures of classes and methods.

Processor

The Processor interface represents a class that processes a message. The signature of this interface is shown below.

Notice that the parameter to the process() method is an Exchange rather than a Message. This provides flexibility. For example, an implementation of this method initially might call exchange.getIn() to get the input message and process it. If an error occurs during processing then the method can call exchange.setException().
An application-level developer might implement the Processor interface with a class that executes some business logic. However, there are many classes in the Camel library that implement the Processor interface in a way that provides support for a design pattern in the
EIP book. For example, ChoiceProcessor implements the message router pattern, that is, it uses a cascading if-then-else statement to route a message from an input queue to one of several output queues. Another example is the FilterProcessor class which discards messages that do not satisfy a stated predicate (that is, condition).

Routes, RouteBuilders and Java DSL

A route is the step-by-step movement of a Message from an input queue, through arbitrary types of decision making (such as filters and routers) to a destination queue (if any). Camel provides two ways for an application developer to specify routes. One way is to specify route information in an XML file. A discussion of that approach is outside the scope of this document. The other way is through what Camel calls a Java DSL (domain-specific language).

Introduction to Java DSL

For many people, the term "domain-specific language" implies a compiler or interpreter that can process an input file containing keywords and syntax specific to a particular domain. This is not the approach taken by Camel. Camel documentation consistently uses the term "Java DSL" instead of "DSL", but this does not entirely avoid potential confusion. The Camel "Java DSL" is a class library that can be used in a way that looks almost like a DSL, except that it has a bit of Java syntactic baggage. You can see this in the example below. Comments afterwards explain some of the constructs used in the example.

The first line in the above example creates an object which is an instance of an anonymous subclass of RouteBuilder with the specified configure() method.
The CamelContext.addRoutes(RouterBuilder builder) method invokes builder.setContext(this) Ð so the RouteBuilder object knows which CamelContext object it is associated with Ð and then invokes builder.configure(). The body of configure() invokes methods such as from(), filter(), choice(), when(), isEqualTo(), otherwise() and to().
The RouteBuilder.from(String uri) method invokes getEndpoint(uri) on the CamelContext associated with the RouteBuilder object to get the specified Endpoint and then puts a FromBuilder "wrapper" around this Endpoint. The FromBuilder.filter(Predicate predicate) method creates a FilterProcessor object for the Predicate (that is, condition) object built from the header("foo").isEqualTo("bar") expression. In this way, these operations incrementally build up a Route object (with a RouteBuilder wrapper around it) and add it to the CamelContext object associated with the RouteBuilder.

Critique of Java DSL

The online Camel documentation compares Java DSL favourably against the alternative of configuring routes and endpoints in a XML-based Spring configuration file. In particular, Java DSL is less verbose than its XML counterpart. In addition, many integrated development environments (IDEs) provide an auto-completion feature in their editors. This auto-completion feature works with Java DSL, thereby making it easier for developers to write Java DSL.
However, there is another option that the Camel documentation neglects to consider: that of writing a parser that can process DSL stored in, say, an external file. Currently, Camel does not provide such a DSL parser, and I do not know if it is on the "to do" list of the Camel maintainers. I think that a DSL parser would offer a significant benefit over the current Java DSL. In particular, the DSL would have a syntactic definition that could be expressed in a relatively short BNF form. The effort required by a Camel user to learn how to use DSL by reading this BNF would almost certainly be significantly less than the effort currently required to study the API of the RouterBuilder classes.

Architecture

Camel uses a Java based Routing Domain Specific Language (DSL) or an Xml Configuration to configure routing and mediation rules which are added to a CamelContext to implement the various Enterprise Integration Patterns.

At a high level Camel consists of a CamelContext which contains a collection of Component instances. A Component is essentially a factory of Endpoint instances. You can explicitly configure Component instances in Java code or an IoC container like Spring or Guice, or they can be auto-discovered using URIs.

An Endpoint acts rather like a URI or URL in a web application or a Destination in a JMS system; you can communicate with an endpoint; either sending messages to it or consuming messages from it. You can then create a Producer or Consumer on an Endpoint to exchange messages with it.

The DSL makes heavy use of pluggable Languages to create an Expression or Predicate to make a truly powerful DSL which is extensible to the most suitable language depending on your needs. The following languages are supported

URIs

Camel makes extensive use of URIs to allow you to refer to endpoints which are lazily created by a Component if you refer to them within Routes

Current Supported URIs

Component / URIDescription
ActiveMQ
activemq:[topic:]destinationName
For JMS Messaging with Apache ActiveMQ
ActiveMQ Journal
activemq.journal:directory-on-filesystem
Uses ActiveMQ's fast disk journaling implementation to store message bodies in a rolling log file
AMQP
amqp:[topic:]destinationName
For Messaging with AMQP protocol
Bean
bean:beanName[?methodName=someMethod]
Uses the Bean Binding to bind message exchanges to beans in the Registry
CXF
cxf:serviceName
Working with Apache CXF for web services integration
DataSet
dataset:name
For load & soak testing the DataSet provides a way to create huge numbers of messages for sending to Components or asserting that they are consumed correctly
Direct
direct:name
Direct invocation of the consumer from the producer so that single threaded (non-SEDA) in VM invocation is performed
Esper
esper:name
Working with the Esper Library for Event Stream Processing
Event
event://default
Working with Spring ApplicationEvents
File
file://nameOfFileOrDirectory
Sending messages to a file or polling a file or directory
FIX
fix://configurationResource
Sends or receives messages using the FIX protocol
FTP
ftp://host[:port]/fileName
Sending and receiving files over FTP
HTTP
http://hostname[:port]
For calling out to external HTTP servers
iBATIS
ibatis://sqlOperationName
Performs a query, poll, insert, update or delete in a relational database using Apache iBATIS
IMap
imap://hostname[:port]
Receiving email using IMap
IRC
irc:host[:port]/#room
For IRC communication
JDBC
jdbc:dataSourceName?options
For performing JDBC queries and operations
Jetty
jetty:url
For exposing services over HTTP
JBI
jbi:serviceName
For JBI integration such as working with Apache ServiceMix
JMS
jms:[topic:]destinationName
Working with JMS providers
JPA
jpa://entityName
For using a database as a queue via the JPA specification for working with OpenJPA, Hibernate or TopLink
List
list:someName
Provdes a simple BrowsableEndpoint which can be useful for testing, visualisation tools or debugging. The exchanges sent to the endpoint are all available to be browsed.
Log
log:loggingCategory[?level=ERROR]
Uses Jakarta Commons Logging to log the message exchange to some underlying logging system like log4j
Mail
mail://user-info@host:port
Sending and receiving email
MINA
[tcp|udp|multicast]:host[:port]
Working with Apache MINA
Mock
mock:name
For testing routes and mediation rules using mocks
MSV
msv:someLocalOrRemoteResource
Validates the payload of a message using the MSV Library
Multicast
multicast://host:port
Working with TCP protocols using Apache MINA
Pojo
pojo:name
Exposing and invoking a POJO
POP
pop3://user-info@host:port
Receiving email using POP3 and JavaMail
Quartz
quartz://groupName/timerName
Provides a scheduled delivery of messages using the Quartz scheduler
Queue
queue:name
Deprecated.Ê It is now an alias toÊthe SEDA component.
RMI
rmi://host[:port]
Working with RMI
RNC
rnc:/relativeOrAbsoluteUri
Validates the payload of a message using RelaxNG Compact Syntax
RNG
rng:/relativeOrAbsoluteUri
Validates the payload of a message using RelaxNG
SEDA
seda:name
Used to deliver messages to a java.util.concurrent.BlockingQueue, useful when creating SEDA style processing pipelines within the same CamelContext
SFTP
sftp://host[:port]/fileName
Sending and receiving files over SFTP
SMTP
smtp://user-info@host[:port]
Sending email using SMTP and JavaMail
Stream
stream:[in|out|err|file]
Read or write to an input/output/error/file stream rather like unix pipes
StringTemplate
string-template:someTemplateResource
Generates a response using a String Template
Timer
timer://name
A timer endpoint
TCP
tcp://host:port
Working with TCP protocols using Apache MINA
Test
test:expectedMessagesEndpointUri
Creates a Mock endpoint which expects to receive all the message bodies that could be polled from the given underlying endpoint
UDP
udp://host:port
Working with UDP protocols using Apache MINA
Validation
validation:someLocalOrRemoteResource
Validates the payload of a message using XML Schema and JAXP Validation
Velocity
velocity:someTemplateResource
Generates a response using an Apache Velocity template
VM
vm:name
Used to deliver messages to a java.util.concurrent.BlockingQueue, useful when creating SEDA style processing pipelines within the same JVM
XMPP
xmpp://host:port/room
Working with XMPP and Jabber
XQuery
xquery:someXQueryResource
Generates a response using an XQuery template
XSLT
xslt:someTemplateResource
Generates a response using an XSLT template
WebDAV
webdav://host[:port]/fileName
Sending and receiving files over WebDAV
MSMQ
msmq:msmqQueueName
Sending and receiving messages with Microsoft Message Queuing

For a full details of the individual components see the Component Appendix

Enterprise Integration Patterns

Camel supports most of the Enterprise Integration Patterns from the excellent book of the same name by Gregor Hohpe and Bobby Woolf. Its a highly recommended book, particularly for users of Camel.

Pattern Index

There now follows a list of the Enterprise Integration Patterns from the book along with examples of the various patterns using Apache Camel

Messaging Systems

Message Channel How does one application communicate with another using messaging?
Message How can two applications connected by a message channel exchange a piece of information?
Pipes and Filters How can we perform complex processing on a message while maintaining independence and flexibility?
Message Router How can you decouple individual processing steps so that messages can be passed to different filters depending on a set of conditions?
Message Translator How can systems using different data formats communicate with each other using messaging?
Message Endpoint How does an application connect to a messaging channel to send and receive messages?

Messaging Channels

Point to Point Channel How can the caller be sure that exactly one receiver will receive the document or perform the call?
Publish Subscribe Channel How can the sender broadcast an event to all interested receivers?
Dead Letter Channel What will the messaging system do with a message it cannot deliver?
Guaranteed Delivery How can the sender make sure that a message will be delivered, even if the messaging system fails?
Message Bus What is an architecture that enables separate applications to work together, but in a de-coupled fashion such that applications can be easily added or removed without affecting the others?

Message Construction

Correlation Identifier How does a requestor that has received a reply know which request this is the reply for?

Message Routing

Content Based Router How do we handle a situation where the implementation of a single logical function (e.g., inventory check) is spread across multiple physical systems?
Message Filter How can a component avoid receiving uninteresting messages?
Recipient List How do we route a message to a list of dynamically specified recipients?
Splitter How can we process a message if it contains multiple elements, each of which may have to be processed in a different way?
Aggregator How do we combine the results of individual, but related messages so that they can be processed as a whole?
Resequencer How can we get a stream of related but out-of-sequence messages back into the correct order?
Routing Slip How do we route a message consecutively through a series of processing steps when the sequence of steps is not known at design-time and may vary for each message?
Unable to render embedded object: File (clear.png) not found. Throttler How can I throttle messages to ensure that a specific endpoint does not get overloaded, or we don't exceed an agreed SLA with some external service?
Unable to render embedded object: File (clear.png) not found. Delayer How can I delay the sending of a message?
Unable to render embedded object: File (clear.png) not found. Load Balancer How can I balance load across a number of endpoints?
Unable to render embedded object: File (clear.png) not found. Multicast How can I route a message to a number of endpoints at the same time?

Message Transformation

Content Enricher How do we communicate with another system if the message originator does not have all the required data items available?
Content Filter How do you simplify dealing with a large message, when you are interested only in a few data items?
Normalizer How do you process messages that are semantically equivalent, but arrive in a different format?

Messaging Endpoints

Unable to render embedded object: File (clear.png) not found. Messaging Mapper How do you move data between domain objects and the messaging infrastructure while keeping the two independent of each other?
Event Driven Consumer How can an application automatically consume messages as they become available?
Polling Consumer How can an application consume a message when the application is ready?
Competing Consumers How can a messaging client process multiple messages concurrently?
Message Dispatcher How can multiple consumers on a single channel coordinate their message processing?
Selective Consumer How can a message consumer select which messages it wishes to receive?
Durable Subscriber How can a subscriber avoid missing messages while it's not listening for them?
Unable to render embedded object: File (clear.png) not found. Idempotent Consumer How can a message receiver deal with duplicate messages?
Transactional Client How can a client control its transactions with the messaging system?
Messaging Gateway How do you encapsulate access to the messaging system from the rest of the application?
Service Activator How can an application design a service to be invoked both via various messaging technologies and via non-messaging techniques?

System Management

Wire Tap How do you inspect messages that travel on a point-to-point channel?

For a full breakdown of each pattern see the Book Pattern Appendix

Pattern Appendix

There now follows a breakdown of the various Enterprise Integration Patterns that Camel supports

Messaging Systems

Message Channel

Camel supports the Message Channel from the EIP patterns. The Message Channel is an internal implementation detail of the Endpoint interface and all interactions with the Message Channel are via the Endpoint interfaces.

For more details see

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

Message

Camel supports the Message from the EIP patterns using the Message interface.

To support various message exchange patterns like one way event messages and request-response messages Camel uses an Exchange interface which is used to handle either oneway messages with a single inbound Message, or request-reply where there is an inbound and outbound message.

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

Pipes and Filters

Camel supports the Pipes and Filters from the EIP patterns in various ways.

With Camel you can split your processing across multiple independent Endpoint instances which can then be chained together.

Using Routing Logic

You can create pipelines of logic using multiple Endpoint or Message Translator instances as follows

from("direct:a").pipeline("direct:x", "direct:y", "direct:z", "mock:result");

In the above example we are routing from a single Endpoint to a list of different endpoints specified using URIs. If you find the above a bit confusing, try reading about the Architecture or try the Examples

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

Message Router

The Message Router from the EIP patterns allows you to consume from an input destination, evaluate some predicate then choose the right output destination.

The following example shows how to route a request from an input queue:a endpoint to either queue:b, queue:c or queue:d depending on the evaluation of various Predicate expressions

Using the Fluent Builders

RouteBuilder builder = new RouteBuilder() {
    public void configure() {
        from("seda:a").choice().when(header("foo").isEqualTo("bar")).to("seda:b")
            .when(header("foo").isEqualTo("cheese")).to("seda:c").otherwise().to("seda:d");
    }
};

Using the Spring XML Extensions

<camelContext id="buildSimpleRouteWithChoice" xmlns="http://activemq.apache.org/camel/schema/spring">
  <route>
    <from uri="seda:a"/>
    <choice>
      <when>
        <predicate>
          <header name="foo"/>
          <isEqualTo value="bar"/>
        </predicate>
        <to uri="seda:b"/>
      </when>
      <when>
        <predicate>
          <header name="foo"/>
          <isEqualTo value="cheese"/>
        </predicate>
        <to uri="seda:c"/>
      </when>
      <otherwise>
        <to uri="seda:d"/>
      </otherwise>
    </choice>
  </route>
</camelContext>

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

Message Translator

Camel supports the Message Translator from the EIP patterns by using an arbitrary Processor in the routing logic or by using a bean in the Bean Integration to perform the transformation. You can also use a Data Format to marshal and unmarshal messages in different encodings.

Using the Fluent Builders

You can transform a message using Camel's Bean Integration to call any method on a bean in your Registry such as your Spring XML configuration file as follows

from("activemq:SomeQueue").
  beanRef("myTransformerBean", "myMethodName").
  to("mqseries:AnotherQueue");

Where the "myTransformerBean" would be defined in a Spring XML file or defined in JNDI etc. You can omit the method name parameter from beanRef() and the Bean Integration will try to deduce the method to invoke from the message exchange.

or you can add your own explicit Processor to do the transformation

from("direct:start").process(new Processor() {
    public void process(Exchange exchange) {
        Message in = exchange.getIn();
        in.setBody(in.getBody(String.class) + " World!");
    }
}).to("mock:result");

or you can use the DSL to explicitly configure the transformation

from("direct:start").setBody(body().append(" World!")).to("mock:result");

You can also use Templating to consume a message from one destination, transform it with something like Velocity or XQuery and then send it on to another destination. For example using InOnly (one way messaging)

from("activemq:My.Queue").
  to("velocity:com/acme/MyResponse.vm").
  to("activemq:Another.Queue");

If you want to use InOut (request-reply) semantics to process requests on the My.Queue queue on ActiveMQ with a template generated response, then sending responses back to the JMSReplyTo Destination you could use this.

from("activemq:My.Queue").
  to("velocity:com/acme/MyResponse.vm");

For further examples of this pattern in use you could look at one of the JUnit tests

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

Message Endpoint

Camel supports the Message Endpoint from the EIP patterns using the Endpoint interface.

When using the DSL to create Routes you typically refer to Message Endpoints by their URIs rather than directly using the Endpoint interface. Its then a responsibility of the CamelContext to create and activate the necessary Endpoint instances using the available Component implementations.

For more details see

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

Messaging Channels

Point to Point Channel

Camel supports the Point to Point Channel from the EIP patterns using the following components

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

Publish Subscribe Channel

Camel supports the Publish Subscribe Channel from the EIP patterns using the following components

Using Routing Logic

Another option is to explicitly list the publish-subscribe relationship in your routing logic; this keeps the producer and consumer decoupled but lets you control the fine grained routing configuration using the DSL or Xml Configuration.

Using the Fluent Builders

RouteBuilder builder = new RouteBuilder() {
    public void configure() {
        from("seda:a").to("seda:b", "seda:c", "seda:d");
    }
};

Using the Spring XML Extensions

<camelContext id="buildStaticRecipientList" xmlns="http://activemq.apache.org/camel/schema/spring">
  <route>
    <from uri="seda:a"/>
    <to>
      <uri>seda:b</uri>
      <uri>seda:c</uri>
      <uri>seda:d</uri>
    </to>
  </route>
</camelContext>

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

Dead Letter Channel

Camel supports the Dead Letter Channel from the EIP patterns using the DeadLetterChannel processor which is an Error Handler.

Redelivery

It is common for a temporary outage or database deadlock to cause a message to fail to process; but the chances are if its tried a few more times with some time delay then it will complete fine. So we typically wish to use some kind of redelivery policy to decide how many times to try redeliver a message and how long to wait before redelivery attempts.

The RedeliveryPolicy defines how the message is to be redelivered. You can customize things like

Once all attempts at redelivering the message fails then the message is forwarded to the dead letter queue.

Redelivery header

When a message is redelivered the DeadLetterChannel will append a customizable header to the message to indicate how many times its been redelivered. The default value is org.apache.camel.redeliveryCount.

Configuring via the DSL

The following example shows how to configure the Dead Letter Channel configuration using the DSL

RouteBuilder builder = new RouteBuilder() {
    public void configure() {
        errorHandler(deadLetterChannel("seda:errors"));
        from("seda:a").to("seda:b");
    }
};

You can also configure the RedeliveryPolicy as this example shows

RouteBuilder builder = new RouteBuilder() {
    public void configure() {
        errorHandler(deadLetterChannel("seda:errors").maximumRedeliveries(2).useExponentialBackOff());
        from("seda:a").to("seda:b");
    }
};

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

Guaranteed Delivery

Camel supports the Guaranteed Delivery from the EIP patterns using the following components

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

Message Bus

Camel supports the Message Bus from the EIP patterns. You could view Camel as a Message Bus itself as it allows producers and consumers to be decoupled.

Folks often assume that a Message Bus is a JMS though so you may wish to refer to the JMS component for traditional MOM support.

Also worthy of node is the XMPP component for supporting messaging over XMPP (Jabber)

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

Message Routing

Content Based Router

The Content Based Router from the EIP patterns allows you to route messages to the correct destination based on the contents of the message exchanges.

The following example shows how to route a request from an input queue:a endpoint to either queue:b, queue:c or queue:d depending on the evaluation of various Predicate expressions

Using the Fluent Builders

RouteBuilder builder = new RouteBuilder() {
    public void configure() {
        from("seda:a").choice().when(header("foo").isEqualTo("bar")).to("seda:b")
            .when(header("foo").isEqualTo("cheese")).to("seda:c").otherwise().to("seda:d");
    }
};

Using the Spring XML Extensions

<camelContext id="buildSimpleRouteWithChoice" xmlns="http://activemq.apache.org/camel/schema/spring">
  <route>
    <from uri="seda:a"/>
    <choice>
      <when>
        <predicate>
          <header name="foo"/>
          <isEqualTo value="bar"/>
        </predicate>
        <to uri="seda:b"/>
      </when>
      <when>
        <predicate>
          <header name="foo"/>
          <isEqualTo value="cheese"/>
        </predicate>
        <to uri="seda:c"/>
      </when>
      <otherwise>
        <to uri="seda:d"/>
      </otherwise>
    </choice>
  </route>
</camelContext>

For further examples of this pattern in use you could look at the junit test case

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

Message Filter

The Message Filter from the EIP patterns allows you to filter messages

The following example shows how to create a Message Filter route consuming messages from an endpoint called queue:a which if the Predicate is true will be dispatched to queue:b

Using the Fluent Builders

RouteBuilder builder = new RouteBuilder() {
    public void configure() {
        from("seda:a").filter(header("foo").isEqualTo("bar")).to("seda:b");
    }
};

You can of course use many different Predicate languages such as XPath, XQuery, SQL or various Scripting Languages. Here is an XPath example

from("direct:start").
        filter().xpath("/person[@name='James']").
        to("mock:result");

Using the Spring XML Extensions

<camelContext id="buildSimpleRouteWithHeaderPredicate" xmlns="http://activemq.apache.org/camel/schema/spring">
  <route>
    <from uri="seda:a"/>
    <filter>
      <predicate>
        <header name="foo"/>
        <isEqualTo value="bar"/>
      </predicate>
    </filter>
    <to uri="seda:b"/>
  </route>
</camelContext>

For further examples of this pattern in use you could look at the junit test case

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

Recipient List

The Recipient List from the EIP patterns allows you to route messages to a number of destinations.

Static Recipient List

The following example shows how to route a request from an input queue:a endpoint to a static list of destinations

Using the Fluent Builders

RouteBuilder builder = new RouteBuilder() {
    public void configure() {
        from("seda:a").to("seda:b", "seda:c", "seda:d");
    }
};

Using the Spring XML Extensions

<camelContext id="buildStaticRecipientList" xmlns="http://activemq.apache.org/camel/schema/spring">
  <route>
    <from uri="seda:a"/>
    <to>
      <uri>seda:b</uri>
      <uri>seda:c</uri>
      <uri>seda:d</uri>
    </to>
  </route>
</camelContext>

Dynamic Recipient List

Usually one of the main reasons for using the Recipient List pattern is that the list of recipients is dynamic and calculated at runtime. The following example demonstrates how to create a dynamic recipient list using an Expression (which in this case it extracts a named header value dynamically) to calculate the list of endpoints which are either of type Endpoint or are converted to a String and then resolved using the endpoint URIs.

Using the Fluent Builders

RouteBuilder builder = new RouteBuilder() {
    public void configure() {
        from("seda:a").recipientList(header("foo"));
    }
};

The above assumes that the header contains a list of endpoint URIs. The following takes a single string header and tokenizes it

from("direct:a").recipientList(
        header("recipientListHeader").tokenize(","));

Using the Spring XML Extensions

<camelContext id="buildDynamicRecipientList" xmlns="http://activemq.apache.org/camel/schema/spring">
  <route>
    <from uri="seda:a"/>
    <recipientList>
      <recipients>
        <header name="foo"/>
      </recipients>
    </recipientList>
  </route>
</camelContext>

For further examples of this pattern in use you could look at one of the junit test case

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

Splitter

The Splitter from the EIP patterns allows you split a message into a number of pieces and process them individually

Example

The following example shows how to take a request from the queue:a endpoint the split it into pieces using an Expression, then forward each piece to queue:b

Using the Fluent Builders

RouteBuilder builder = new RouteBuilder() {
    public void configure() {
        from("seda:a").splitter(bodyAs(String.class).tokenize("\n")).to("seda:b");
    }
};

The splitter can use any Expression language so you could use any of the Languages Supported such as XPath, XQuery, SQL or one of the Scripting Languages to perform the split. e.g.

from("activemq:my.queue").splitter(xpath("//foo/bar")).to("file://some/directory")

Using the Spring XML Extensions

<camelContext id="buildSplitter" xmlns="http://activemq.apache.org/camel/schema/spring">
    <route>
      <from uri="seda:a"/>
      <splitter>
        <recipients>
          <bodyAs class="java.lang.String"/>
          <tokenize token="
"/>
        </recipients>
      </splitter>
      <to uri="seda:b"/>
    </route>
  </camelContext>

For further examples of this pattern in use you could look at one of the junit test case

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

Resequencer

The Resequencer from the EIP patterns allows you to reorganise messages based on some comparator. By default in Camel we use an Expression to create the comparator; so that you can compare by a message header or the body or a piece of a message etc.

Camel supports two resequencing algorithms:

Batch Resequencing

The following example shows how to use the batch-processing resequencer so that messages are sorted in order of the body() expression. That is messages are collected into a batch (either by a maximum number of messages per batch or using a timeout) then they are sorted in order and then sent out to their output.

Using the Fluent Builders

from("direct:start").resequencer(body()).to("mock:result");

This is equvalent to

from("direct:start").resequencer(body()).batch().to("mock:result");

To define a custom configuration for the batch-processing resequencer you should provide a configuration object.

from("direct:start").resequencer(body()).batch(new BatchResequencerConfig(300, 4000L)).to("mock:result")

This sets the batchSize to 300 and the batchTimeout to 4000 ms (by default, the batch size is 100 and the timeout is 1000 ms).

So the above example will reorder messages from endpoint direct:a in order of their bodies, to the endpoint mock:result. Typically you'd use a header rather than the body to order things; or maybe a part of the body. So you could replace this expression with

resequencer(header("JMSPriority"))

for example to reorder messages using their JMS priority.

You can of course use many different Expression languages such as XPath, XQuery, SQL or various Scripting Languages.

You can also use multiple expressions; so you could for example sort by priority first then some other custom header

resequencer(header("JMSPriority"), header("MyCustomerRating"))

Using the Spring XML Extensions

<camelContext id="camel" xmlns="http://activemq.apache.org/camel/schema/spring">
  <route>
    <from uri="direct:start" />
    <resequencer>
      <simple>body</simple>
      <to uri="mock:result" />
      <!-- 
        batch-config can be ommitted for default (batch) resequencer settings
      -->
      <batch-config batchSize="300" batchTimeout="4000" />
    </resequencer>
  </route>
</camelContext>

Stream Resequencing

The next example shows how to use the stream-processing resequencer. Messages are re-ordered based on their sequence numbers given by a seqnum header using gap detection and timeouts on the level of individual messages.

Using the Fluent Builders

from("direct:start").resequencer(header("seqnum")).stream().to("mock:result");

To define a custom configuration for the stream-processing resequencer you should provide a configuration object.

from("direct:start").resequencer(header("seqnum")).stream(new StreamResequencerConfig(5000, 4000L)).to("mock:result")

This sets the resequencer's capacity to 5000 and the timeout to 4000 ms (by default, the capacity is 100 and the timeout is 1000 ms).

The stream-processing resequencer algorithm is based on the detection of gaps in a message stream rather than on a fixed batch size. Gap detection in combination with timeouts removes the constraint of having to know the number of messages of a sequence (i.e. the batch size) in advance. Messages must contain a unique sequence number for which a predecessor and a successor is known. For example a message with the sequence number 3 has a predecessor message with the sequence number 2 and a successor message with the sequence number 4. The message sequence 2,3,5 has a gap because the sucessor of 3 is missing. The resequencer therefore has to retain message 5 until message 4 arrives (or a timeout occurs).

If the maximum time difference between messages (with successor/predecessor relationship with respect to the sequence number) in a message stream is known, then the resequencer's timeout parameter should be set to this value. In this case it is guaranteed that all messages of a stream are delivered in correct order to the next processor. The lower the timeout value is compared to the out-of-sequence time difference the higher is the probability for out-of-sequence messages delivered by this resequencer. Large timeout values should be supported by sufficiently high capacity values. The capacity parameter is used to prevent the resequencer from running out of memory.

By default, the stream resequencer expects long sequence numbers but other sequence numbers types can be supported as well by providing custom comparators.

ExpressionResultComparator<Exchange> comparator = new MyComparator();
StreamResequencerConfig config = new StreamResequencerConfig(5000, 4000L, comparator);
from("direct:start").resequencer(header("seqnum")).stream(config).to("mock:result");

Using the Spring XML Extensions

<camelContext id="camel" xmlns="http://activemq.apache.org/camel/schema/spring">
  <route>
    <from uri="direct:start"/>
    <resequencer>
      <simple>in.header.seqnum</simple>
      <to uri="mock:result" />
      <stream-config capacity="5000" timeout="4000"/>
    </resequencer>
  </route>
</camelContext>

Further Examples

For further examples of this pattern in use you could look at the batch-processing resequencer junit test case and the stream-processing resequencer junit test case

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

Message Transformation

Content Enricher

Camel supports the Content Enricher from the EIP patterns using a Message Translator or by using an artibrary Processor in the routing logic to enrich the message.

Using the Fluent Builders

You can use Templating to consume a message from one destination, transform it with something like Velocity or XQuery and then send it on to another destination. For example using InOnly (one way messaging)

from("activemq:My.Queue").
  to("velocity:com/acme/MyResponse.vm").
  to("activemq:Another.Queue");

If you want to use InOut (request-reply) semantics to process requests on the My.Queue queue on ActiveMQ with a template generated response, then sending responses back to the JMSReplyTo Destination you could use this.

from("activemq:My.Queue").
  to("velocity:com/acme/MyResponse.vm");

Here is a simple example using the DSL directly to transform the message body

from("direct:start").setBody(body().append(" World!")).to("mock:result");

In this example we add our own Processor using explicit Java code

from("direct:start").process(new Processor() {
    public void process(Exchange exchange) {
        Message in = exchange.getIn();
        in.setBody(in.getBody(String.class) + " World!");
    }
}).to("mock:result");

Finally we can use Bean Integration to use any Java method on any bean to act as the transformer

Content Enricher

Camel supports the Content Enricher from the EIP patterns using a Message Translator or by using an artibrary Processor in the routing logic to enrich the message.

Using the Fluent Builders

You can use Templating to consume a message from one destination, transform it with something like Velocity or XQuery and then send it on to another destination. For example using InOnly (one way messaging)

from("activemq:My.Queue").
  beanRef("myBeanName", "myMethodName").
  to("activemq:Another.Queue");

For further examples of this pattern in use you could look at one of the JUnit tests

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

Content Filter

Camel supports the Content Filter from the EIP patterns using a Message Translator or by using an artibrary Processor in the routing logic to filter content from the inbound message.

A common way to filter messages is to use an Expression in the DSL like XQuery, SQL or one of the supported Scripting Languages.

Using the Fluent Builders

Here is a simple example using the DSL directly

from("direct:start").setBody(body().append(" World!")).to("mock:result");

In this example we add our own Processor

from("direct:start").process(new Processor() {
    public void process(Exchange exchange) {
        Message in = exchange.getIn();
        in.setBody(in.getBody(String.class) + " World!");
    }
}).to("mock:result");

For further examples of this pattern in use you could look at one of the JUnit tests

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

Normalizer

Camel supports the Normalizer from the EIP patterns by using a Message Router in front of a number of Message Translator instances.

See Also

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

Messaging Endpoints

Messaging Mapper

Camel supports the Messaging Mapper from the EIP patterns by using either Message Translator pattern or the Type Converter module.

See also

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

Event Driven Consumer

Camel supports the Event Driven Consumer from the EIP patterns. The default consumer model is event based (i.e. asynchronous) as this means that the Camel container can then manage pooling, threading and concurrency for you in a declarative manner.

The Event Driven Consumer is implemented by consumers implementing the Processor interface which is invoked by the Message Endpoint when a Message is available for processing.

For more details see

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

Polling Consumer

Camel supports implementing the Polling Consumer from the EIP patterns using the PollingConsumer interface which can be created via the Endpoint.createPollingConsumer() method.

So in your Java code you can do

Endpoint endpoint = context.getEndpoint("activemq:my.queue");
PollingConsumer consumer = endpoint.createPollingConsumer();
Exchange exchange = consumer.receive();

There are 3 main polling methods on PollingConsumer

Method nameDescription
receive() Waits until a message is available and then returns it; potentially blocking forever
receive(long) Attempts to receive a message exchange, waiting up to the given timeout and returning null if no message exchange could be received within the time available
receiveNoWait() Attempts to receive a message exchange immediately without waiting and returning null if a message exchange is not available yet

Scheduled Poll Components

Quite a few inbound Camel endpoints use a scheduled poll pattern to receive messages and push them through the Camel processing routes. That is to say externally from the client the endpoint appears to use an Event Driven Consumer but internally a scheduled poll is used to monitor some kind of state or resource and then fire message exchanges.

Since this a such a common pattern, polling components can extend the ScheduledPollConsumer base class which makes it simpler to implement this pattern.

There is also the Quartz Component which provides scheduled delivery of messages using the Quartz enterprise scheduler.

For more details see

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

Competing Consumers

Camel supports the Competing Consumers from the EIP patterns using a few different components.

You can use the following components to implement competing consumers:-

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

Message Dispatcher

Camel supports the Message Dispatcher from the EIP patterns using various approaches.

You can use a component like JMS with selectors to implement a Selective Consumer as the Message Dispatcher implementation. Or you can use an Endpoint as the Message Dispatcher itself and then use a Content Based Router as the Message Dispatcher.

See Also

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

Selective Consumer

The Selective Consumer from the EIP patterns can be implemented in two ways

The first solution is to provide a Message Selector to the underlying URIs when creating your consumer. For example when using JMS you can specify a selector parameter so that the message broker will only deliver messages matching your criteria.

The other approach is to use a Message Filter which is applied; then if the filter matches the message your consumer is invoked as shown in the following example

Using the Fluent Builders

RouteBuilder builder = new RouteBuilder() {
    public void configure() {
        from("seda:a").filter(header("foo").isEqualTo("bar")).process(myProcessor);
    }
};

Using the Spring XML Extensions

<camelContext id="buildCustomProcessorWithFilter" xmlns="http://activemq.apache.org/camel/schema/spring">
  <route>
    <from uri="seda:a"/>
    <filter>
      <predicate>
        <header name="foo"/>
        <isEqualTo value="bar"/>
      </predicate>
    </filter>
    <process ref="#myProcessor"/>
  </route>
</camelContext>

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

Durable Subscriber

Camel supports the Durable Subscriber from the EIP patterns using the JMS component which supports publish & subscribe using Topics with support for non-durable and durable subscribers.

Another alternative is to combine the Message Dispatcher or Content Based Router with File or JPA components for durable subscribers then something like Queue for non-durable.

See Also

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

Idempotent Consumer

The Idempotent Consumer from the EIP patterns is used to filter out duplicate messages.

This pattern is implemented using the IdempotentConsumer class. This uses an Expression to calculate a unique message ID string for a given message exchange; this ID can then be looked up in the MessageIdRepository to see if it has been seen before; if it has the message is consumed; if its not then the message is processed and the ID is added to the repository.

The Idempotent Consumer essentially acts like a Message Filter to filter out duplicates.

Using the Fluent Builders

The following example will use the header myMessageId to filter out duplicates

RouteBuilder builder = new RouteBuilder() {
    public void configure() {
        from("seda:a").idempotentConsumer(header("myMessageId"), memoryMessageIdRepository(200))
            .to("seda:b");
    }
};

The above example will use an in-memory based MessageIdRepository which can easily run out of memory and doesn't work in a clustered environment. So you might prefer to use the JPA based implementation which uses a database to store the message IDs which have been processed

return new SpringRouteBuilder() {
    public void configure() {
        from("direct:start").idempotentConsumer(
                header("messageId"),
                jpaMessageIdRepository(bean(JpaTemplate.class), PROCESSOR_NAME)
        ).to("mock:result");
    }
};

In the above example we are using the header messageId to filter out duplicates and using the collection myProcessorName to indicate the Message ID Repository to use. This name is important as you could process the same message by many different processors; so each may require its own logical Message ID Repository.

Using the Spring XML Extensions

<camelContext id="buildCustomProcessorWithFilter" xmlns="http://activemq.apache.org/camel/schema/spring">
  <route>
    <from uri="seda:a"/>
    <filter>
      <predicate>
        <header name="foo"/>
        <isEqualTo value="bar"/>
      </predicate>
    </filter>
    <process ref="#myProcessor"/>
  </route>
</camelContext>

For further examples of this pattern in use you could look at the junit test case

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

Transactional Client

Camel recommends supporting the Transactional Client from the EIP patterns using spring transactions.

Transaction Oriented Endpoints (Camel Toes) like JMS support using a transaction for both inbound and outbound message exchanges. Endpoints that support transactions will participate in the current transaction context that they are called from.

You should use the SpringRouteBuilder to setup the routes since you will need to setup the spring context with the TransactionTemplates that will define the transaction manager configuration and policies.

For inbound endpoint to be transacted, they normally need to be configured to use a Spring PlatformTransactionManager. In the case of the JMS component, this can be done by looking it up in the spring context.

You first define needed object in the spring configuration.

<bean id="jmsTransactionManager" class="org.springframework.jms.connection.JmsTransactionManager">
    <property name="connectionFactory" ref="jmsConnectionFactory" />
  </bean>
  
  <bean id="jmsConnectionFactory" class="org.apache.activemq.ActiveMQConnectionFactory">
    <property name="brokerURL" value="tcp://localhost:61616"/>
  </bean>

Then you look them up and use them to create the JmsComponent.

PlatformTransactionManager transactionManager = (PlatformTransactionManager) spring.getBean("jmsTransactionManager");
  ConnectionFactory connectionFactory = (ConnectionFactory) spring.getBean("jmsConnectionFactory");
  JmsComponent component = JmsComponent.jmsComponentTransacted(connectionFactory, transactionManager);
  component.getConfiguration().setConcurrentConsumers(1);
  ctx.addComponent("activemq", component);

Transaction Policies

Outbound endpoints will automatically enlist in the current transaction context. But what if you do not want your outbound endpoint to enlist in the same transaction as your inbound endpoint? The solution is to add a Transaction Policy to the processing route. You first have to define transaction policies that you will be using. The policies use a spring TransactionTemplate to declare the transaction demarcation use. So you will need to add something like the following to your spring xml:

<bean id="PROPAGATION_REQUIRED" class="org.springframework.transaction.support.TransactionTemplate">
    <property name="transactionManager" ref="jmsTransactionManager"/>
  </bean>
  
  <bean id="PROPAGATION_NOT_SUPPORTED" class="org.springframework.transaction.support.TransactionTemplate">
    <property name="transactionManager" ref="jmsTransactionManager"/>
    <property name="propagationBehaviorName" value="PROPAGATION_NOT_SUPPORTED"/>
  </bean>

  <bean id="PROPAGATION_REQUIRES_NEW" class="org.springframework.transaction.support.TransactionTemplate">
    <property name="transactionManager" ref="jmsTransactionManager"/>
    <property name="propagationBehaviorName" value="PROPAGATION_REQUIRES_NEW"/>
  </bean>

Then in your SpringRouteBuilder, you just need to create new SpringTransactionPolicy objects for each of the templates.

public void configure() {
   ...
   Policy requried = new SpringTransactionPolicy(bean(TransactionTemplate.class, "PROPAGATION_REQUIRED"));
   Policy notsupported = new SpringTransactionPolicy(bean(TransactionTemplate.class, "PROPAGATION_NOT_SUPPORTED"));
   Policy requirenew = new SpringTransactionPolicy(bean(TransactionTemplate.class, "PROPAGATION_REQUIRES_NEW"));
   ...
}

Once created, you can use the Policy objects in your processing routes:

// Send to bar in a new transaction
   from("activemq:queue:foo").policy(requirenew).to("activemq:queue:bar");

   // Send to bar without a transaction.
   from("activemq:queue:foo").policy(notsupported ).to("activemq:queue:bar");

See Also

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

Messaging Gateway

Camel has several endpoint components that support the Messaging Gateway from the EIP patterns.

Components like Bean, CXF and Pojo provide a a way to bind a Java interface to the message exchange.

See Also

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

Service Activator

Camel has several endpoint components that support the Service Activator from the EIP patterns.

Components like Bean, CXF and Pojo provide a a way to bind the message exchange to a Java interface/service.

See Also

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

System Management

Wire Tap

The Wire Tap from the EIP patterns allows you to route messages to a separate tap location before it is forwarded to the ultimate destination.

The following example shows how to route a request from an input queue:a endpoint to the wire tap location queue:tap before it is received by queue:b

Using the Fluent Builders

RouteBuilder builder = new RouteBuilder() {
    public void configure() {
        from("seda:a").to("seda:tap", "seda:b");
    }
};

Using the Spring XML Extensions

<camelContext id="buildWireTap" xmlns="http://activemq.apache.org/camel/schema/spring">
  <route>
    <from uri="seda:a"/>
    <to>
      <uri>seda:tap</uri>
      <uri>seda:b</uri>
    </to>
  </route>
</camelContext>

Using This Pattern

If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.

Component Appendix

There now follows the documentation on each Camel component.

ActiveMQ Component

The ActiveMQ component allows messages to be sent to a JMS Queue or Topic; or messages to be consumed from a JMS Queue or Topic using Apache ActiveMQ.

This component is based on the JMS Component and uses Spring's JMS support for declarative transactions, using Spring's JmsTemplate for sending and a MessageListenerContainer for consuming.

To use this component make sure you have the activemq.jar or activemq-core.jar on your classpath along with any Camel dependencies such as camel-core.jar, camel-spring.jar and camel-jms.jar.

URI format

So for example to send to queue FOO.BAR you would use

You can be completely specific if you wish via

If you want to send to a topic called Stocks.Prices then you would use

Configuring the Connection Factory

The following test case shows how to add an ActiveMQComponent to the CamelContext using the activeMQComponent() method while specifying the brokerURL used to connect to ActiveMQ

camelContext.addComponent("activemq", activeMQComponent("vm://localhost?broker.persistent=false"));

Configuring the Connection Factory using Spring XML

You can configure the ActiveMQ broker URL on the ActiveMQComponent as follows

Invoking MessageListener POJOs in a Camel route

The ActiveMQ component also providers a helper Type Converter from a JMS MessageListener to a Processor. This means that the Bean component is capable of invoking any JMS MessageListener bean directly inside any route.

So for example you can create a MessageListener in JMS like this....

public class MyListener implements MessageListener {
   public void onMessage(Message jmsMessage) {
       // ...
   }
}

Then use it in your Camel route as follows

from("file://foo/bar").
  bean(MyListener.class);

i.e. you can reuse any of the Camel Components and easily integrate them into your JMS MessageListener POJO!

See Also

ActiveMQ Journal Component

The ActiveMQ Journal Component allows messages to be stored in a rolling log file and then consumed from that log file. The journal aggregates and batches up concurrent writes so that to overhead of writing and waiting for the disk sync is relatively constant regardless of how many concurrent writes are being done. Therefore, this component supports and encourages you to use multiple concurrent producers to the same journal endpoint.

Each journal endpoint uses a different log file and therefore write batching (and the associated performance boost) does not occur between multiple endpoints.

This component only supports 1 active consumer on the endpoint. After the message is processed by the consumer's processor, the log file is marked and only subsequent messages in the log file will get delivered to consumers.

URI format

So for example to send to the journal located in the /tmp/data directory you would use

Options

NameDefault ValueDescription
syncConsumefalseIf set to true, when the journal is marked after a message is consumed, wait till the Operating System has verified the mark update is safely stored on disk
syncProducetrueIf set to true, wait till the Operating System has verified the message is safely stored on disk

Expected Exchange Data Types

The consumer of a Journal endpoint generates DefaultExchange objects with the in message :

The producer to a Journal endpoint expects an Exchange with an In message where the body can be converted to a ByteSequence or a byte[].

See Also

AMQP

The AMQP component supports the AMQP protocol via the Qpid project.

URI format

You can specify all of the various configuration options of the JMS component after the destination name.

See Also

Bean Component

The bean: component binds beans to Camel message exchanges.

URI format

Where someName can be any string which is used to lookup the bean in the Registry and someMethod defines the name of the method to invoke.

This will use the Bean Binding to map the message exchange to the bean.

Using

The object instance that is used to consume messages must be explicitly registered with the Registry. For example if you are using Spring you must define the bean in the spring.xml; or if you don't use Spring then put the bean in JNDI.

// lets populate the context with the services we need
// note that we could just use a spring.xml file to avoid this step
JndiContext context = new JndiContext();
context.bind("bye", new SayService("Good Bye!"));

CamelContext camelContext = new DefaultCamelContext(context);

Once an endpoint has been registered, you can build Camel routes that use it to process exchanges.

// lets add simple route
camelContext.addRoutes(new RouteBuilder() {
    public void configure() {
        from("direct:hello").to("pojo:bye");
    }
});

A bean: endpoint cannot be defined as the input to the route; i.e. you cannot consume from it, you can only route from some inbound message Endpoint to the bean endpoint as output. So consider using a direct: or queue: endpoint as the input.

You can use the createProxy() methods on ProxyHelper to create a proxy that will generate BeanExchanges and send them to any endpoint:

Endpoint endpoint = camelContext.getEndpoint("direct:hello");
ISay proxy = ProxyHelper.createProxy(endpoint, ISay.class);
String rc = proxy.say();
assertEquals("Good Bye!", rc);

Bean binding

The binding of a Camel Message to a bean method call can occur in different ways

By default the return value is set on the outbound message body.

For example you could write a method like this

public class Foo {

    @MessageDriven(uri = "activemq:my.queue")
    public void doSomething(String body) {
        // process the inbound message here
    }

}

Here Camel with subscribe to an ActiveMQ queue, then convert the message payload to a String (so dealing with TextMessage, ObjectMessage and BytesMessage in JMS), then process this method.

Using Annotations to bind parameters to the Exchange

You can also use the following annotations to bind parameters to different kinds of Expression

AnnotationMeaning
@Body To bind to an inbound message body
@Header To bind to an inbound message header
@Headers To bind to the Map of the inbound message headers
@OutHeader To bind to an outbound message header
@OutHeaders To bind to the Map of the outbound message headers
@Property To bind to a named property on the exchange
@Properties To bind to the property map on the exchange

For example

public class Foo {
    
    @MessageDriven(uri = "activemq:my.queue")
    public void doSomething(@Header('JMSCorrelationID') String correlationID, @Body String body) {
        // process the inbound message here
    }

}

In the above you can now pass the Message.getJMSCorrelationID() as a parameter to the method (using the Type Converter to adapt the value to the type of the parameter).

Finally you don't need the @MessageDriven annotation; as the Camel route could describe which method to invoke.

e.g. a route could look like

from("activemq:someQueue").
  to("bean:myBean");

Here myBean would be looked up in the Registry (such as JNDI or the Spring ApplicationContext), then the body of the message would be used to try figure out what method to call.

If you want to be explicit you can use

from("activemq:someQueue").
  to("bean:myBean?methodName=doSomething");

Using Expression Languages

You can also use any of the Languages supported in Camel to bind expressions to method parameters when using bean integration. For example you can use any of these annotations...

AnnotationDescription
@BeanShell Inject a BeanShell expression
@EL Inject an EL expression
@Groovy Inject a Groovy expression
@JavaScript Inject a JavaScript expression
@OGNL Inject an OGNL expression
@PHP Inject a PHP expression
@Python Inject a Python expression
@Ruby Inject a Ruby expression
@Simple Inject an Simple expression
@XPath Inject an XPath expression
@XQuery Inject an XQuery expression

For example

public class Foo {
    
    @MessageDriven(uri = "activemq:my.queue")
    public void doSomething(@Path("/foo/bar/text()") String correlationID, @Body String body) {
        // process the inbound message here
    }
}

See Also

CXF Component

The cxf: component provides integration with Apache CXF for connecting to JAX-WS services hosted in CXF.

URI format

Where address represents the CXF endpoint's address

Where cxfEndpoint repesents the spring bean's name which presents the CXF endpoint

You could apply the dataFormat options to cxfEndpoint like this

Options

NameDescriptionExampledefault value
wsdlURLThe location of the WSDL.file://local/wsdl/hello.wsdl or wsdl/hello.wsdlÊ
serviceClassThe class name of the SEI(Service Endpoint Interface) class which could have JSR181 annotation or notorg.apache.camel.HelloÊ
serviceNameThe service name this service is implementing, it maps to the wsdl:service@name.{http://org.apache.camel}
ServiceName
Ê
portNameThe port name this service is implementing, it maps to the wsdl:port@name.{http://org.apache.camel}
PortName
Ê
dataFormatWhich data type message that CXF endpoint supportPOJO, PAYLOAD, MESSAGEPOJO

The descriptions of the dataformats

DataFormatDescription
POJOPOJOs (Plain old Java objects) are the Java parameters to the method, it is invoking on the target server.
PAYLOADPAYLOAD is the message payload of the message after message configured in the CXF endpoint is applied.
MESSAGEMESSAGE is the raw message that is received from the transport layer.

Configure the CXF endpoints with spring

You can configure the CXF endpoint with the below spring configuration file , and you can also embedded the endpoint into the camelContext tags.

Be sure to include the JAX-WS schemaLocation attribute specified on the root beans element. This allows CXF to validate the file and is required. Also note the namespace declarations at the end of the <cxf:cxfEndpoint/> tag--these are required because the combined "{namespace}localName" syntax is presently not supported for this tag's attribute values.

The jaxws:endpoint element supports many additional attributes:

NameValue
PortNameThe endpoint name this service is implementing, it maps to the wsdl:port@name. In the format of "ns:PORT_NAME" where ns is a namespace prefix valid at this scope.
serviceNameThe service name this service is implementing, it maps to the wsdl:service@name. In the format of "ns:SERVICE_NAME" where ns is a namespace prefix valid at this scope.
wsdlURLThe location of the WSDL. Can be on the classpath, file system, or be hosted remotely.
bindingIdThe bindingId for the service model to use
addressThe service publish address
busThe bus name that will be used in the jaxws endpoint.
serviceClassThe class name of the SEI(Service Endpoint Interface) class which could have JSR181 annotation or not

It also supports many child elements:

NameValue
cxf:inInterceptorsThe incoming interceptors for this endpoint. A list of <bean>s or <ref>s.
cxf:inFaultInterceptorsThe incoming fault interceptors for this endpoint. A list of <bean>s or <ref>s.
cxf:outInterceptorsThe outgoing interceptors for this endpoint. A list of <bean>s or <ref>s.
cxf:outFaultInterceptorsThe outgoing fault interceptors for this endpoint. A list of <bean>s or <ref>s.
cxf:propertiesA properties map which should be supplied to the JAX-WS endpoint. See below.
cxf:dataBindingYou can specify the which DataBinding will be use in the endpoint , This can be supplied using the Spring <bean class="MyDataBinding"/> syntax.
cxf:bindingYou can specify the BindingFactory for this endpoint to use. This can be supplied using the Spring <bean class="MyBindingFactory"/> syntax.
cxf:featuresThe features that hold the interceptors for this endpoint. A list of <bean>s or <ref>s
cxf:schemaLocationsThe schema locations for endpoint to use. A list of <schemaLocation>s
cxf:serviceFactoryThe service factory for this endpoint to use. This can be supplied using the Spring <bean class="MyServiceFactory"/> syntax

You can find more advanced example which shows how to provide interceptors and properties here:
http://cwiki.apache.org/CXF20DOC/jax-ws-configuration.html

See Also

Direct Component

The direct: component provides direct, synchronous invocation of any consumers when a producer sends a message exchange.
This endpoint can be used connect existing routes or if a client in the same JVM as the Camel router wants to access the routes.

URI format

Where someName can be any string to uniquely identify the endpoint

Options

NameDefault ValueDescription
allowMultipleConsumerstrueIf set to false, then when a second consumer is started on the endpoint, a IllegalStateException is thrown

See Also

Esper

The Esper component supports the Esper Library for Event Stream Processing. The camel-esper library is provided by the Camel Extra project which hosts all *GPL related components for Camel.

URI format

When consuming from an Esper endpoint you must specify a pattern or eql statement to query the event stream.

For example

Options

NameDefault ValueDescription
patternÊThe Esper Pattern expression as a String to filter events
eqlÊThe Esper EQL expression as a String to filter events

Demo

There is a demo which shows how to work with ActiveMQ, Camel and Esper in the Camel Extra project

See Also

Event Component

The event: component provides access to the Spring ApplicationEvent objects. This allows you to publish ApplicationEvent objects to a Spring ApplicationContext or to consume them. You can then use Enterprise Integration Patterns to process them such as Message Filter.

URI format

See Also

File Component

The File component provides access to file systems; allowing files to be processed by any other Camel Components or messages from other components can be saved to disk.

URI format

Where fileName represents the underlying file name

URI Options

NameDefault ValueDescription
initialDelay1000milliseconds before polling the file/directory starts
delay500milliseconds before the next poll of the file/directory
useFixedDelayfalseif true, poll once after the initial delay
recursivetrueif a directory, will look for changes in files in all the sub directories
locktrueif true will lock the file for the duration of the processing
regexPatternnullwill only fire a an exchange for a file that matches the regex pattern
deletefalseIf delete is true then the file will be deleted when it is processed (the default is to move it, see below)
noopfalseIf true then the file is not moved or deleted in any way (see below). This option is good for read only data, or for ETL type requirements
moveNamePrefixnullThe prefix String perpended to the filename when moving it. For example to move processed files into the done directory, set this value to 'done/'
moveNamePostfixnullThe postfix String appended to the filename when moving it. For example to rename processed files from foo to foo.old set this value to '.old'
appendtrueWhen writing do we append to the end of the file, or replace it?

By default the file is locked for the duration of the processing. Also when files are processed they are moved into the .camel directory; so that they appear to be deleted.

Message Headers

The following message headers can be used to affect the behavior of the component

HeaderDescription
org.apache.camel.file.nameSpecifies the output file name (relative to the endpoint directory) to be used for the output message when sending to the endpoint. If this is not present then a generated message ID is used instead

Samples

Read from a directory and write to another directory

Listen on a directory and create a message for each file dropped there. Copy the contents to the outputdir and delete the file in the inputdir.

Read from a directory and process the message in java

Body will be File object pointing to the file that was just dropped to the inputdir directory.

Read files from a directory and send the content to a jms queue

By default the file endpoint sends a FileMessage which contains a File as body. If you send this directly to the jms component the jms message will only contain the File object but not the content. By converting the File to a String the message will contain the file contents what is probably what you want to do.

See Also

FIX

The FIX component supports the FIX protocol by using the QuickFix/J library.

URI format

Where configurationResource points to the QuickFix/J configuration file to define how to connect to FIX. This could be a resource on the classpath or refer to a full URL using http: or file: schemes.

Message Formats

By default this component will attempt to use the Type Converter to turn the inbound message body into a QuickFix Message class and all outputs from FIX will be in the same format.

If you are using the Artix Data Services support then any payload such as files or streams or byte arrays can be converted nicely into FIX messages.

Using camel-fix

To use this module you need to use the FUSE Mediation Router distribution. Or you could just add the following to your pom.xml, substituting the version number for the latest & greatest release.

<dependency>
  <groupId>org.apache.camel</groupId>
  <artifactId>camel-parent</artifactId>
  <version>1.3.0.1-fuse</version>
</dependency>

And ensure you are pointing at the maven repo

<repository>
     <id>open.iona.m2</id>
     <name>IONA Open Source Community Release Repository</name>
     <url>http://repo.open.iona.com/maven2</url>
     <snapshots>
       <enabled>false</enabled>
     </snapshots>
     <releases>
       <enabled>true</enabled>
     </releases>
   </repository>

See Also

FTP/SFTP/WebDAV Component

This component provides access to remote file systems over the FTP, SFTP and WebDAV protocols

URI format

Where filename represents the underlying file name or directory. Can contain nested folders.
The username is currently only possible to provide in the hostname parameter.
If no port number is provided. Camel will provide default values according to the protocol. (ftp = 21, sftp = 22)

Examples

ftp://someone@someftpserver.com/public/upload/images/holiday2008?password=secret&binary=true
ftp://someoneelse@someotherftpserver.co.uk:12049/reports/2008/budget.txt?password=secret&binary=false&directory=false
ftp://publicftpserver.com/download

Options

NameDefault ValueDescription
directorytrueindicates whether or not the given file name should be interpreted by default as a directory or file (as it sometimes hard to be sure with some FTP servers)
passwordnullspecifies the password to use to login to the remote file system
binaryfalsespecifies the file transfer mode BINARY or ASCII. Default is ASCII.

See Also

HTTP Component

The http: component provides HTTP based endpoints for consuming external HTTP resources.

URI format

Usage

You can only produce to endpoints generated by the HTTP component. Therefore it should never be used aas input into your camel Routes. To bind/expose an HTTP endpoint via an http server as input to a camel route, you can use the Jetty Component

See Also

iBATIS

The ibatis: component allows you to query, poll, insert, update and delete data in a relational database using Apache iBATIS.

URI format

Where operationName is the name in the iBATIS XML configuration file which maps to the query, insert, update or delete operation you wish to evaluate.

For example if you wish to poll a database for rows using iBATIS and then send them to a JMS Queue via ActiveMQ you could do

from("ibatis:selectAllAccounts").
    to("activemq:MyQueue");

Or to consume beans from a JMS queue and insert them into a database you could do...

from("activemq:Some.Queue").
  to("ibatis:insertAccount");

Options

NameDefault ValueDescription
initialDelay1000The number of milliseconds until the first poll when polling (consuming)
delay500The number of milliseconds for the subsequent delays after the intial delay
useFixedDelayfalseWhether or not the fixed delay is to be used, to enable a repeated timer

See Also

|

IRC Component

The irc: component implements an IRC (Iternet Relay Chat) transport.

URI format

See Also

JBI Component

The jbi: component is provided by the ServiceMix Camel module and provides integration with a JBI Normalized Message Router such as provided by Apache ServiceMix

URI format

The separator used will be:

For more details of valid JBI URIs see the ServiceMix URI Guide.

Using the jbi:service: or jbi:endpoint: URI forms will set the service QName on the JBI endpoint to the exact one you give. Otherwise the default Camel JBI Service QName will be used which is

{http://activemq.apache.org/camel/schema/jbi}endpoint

Examples

Creating a JBI Service Unit

If you have some Camel routes you want to deploy inside JBI as a Service Unit you can use the JBI Service Unit Archetype to create a new project.

If you have an existing maven project which you need to convert into a JBI Service Unit you may want to refer to the ServiceMix Maven JBI Plugins for further help. Basically you just need to make sure

Your pom.xml should look something like this to enable the jbi-service-unit packaging.

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">

  <modelVersion>4.0.0</modelVersion>

  <groupId>myGroupId</groupId>
  <artifactId>myArtifactId</artifactId>
  <packaging>jbi-service-unit</packaging>
  <version>1.0-SNAPSHOT</version>

  <name>A Camel based JBI Service Unit</name>

  <url>http://www.myorganization.org</url>

  <properties>
    <camel-version>1.0.0</camel-version>
    <servicemix-version>3.2-incubating</servicemix-version>
  </properties>

  <dependencies>
    <dependency>
      <groupId>org.apache.camel</groupId>
      <artifactId>camel-jbi</artifactId>
      <version>${camel-version}</version>
    </dependency>

    <dependency>
      <groupId>org.apache.servicemix</groupId>
      <artifactId>servicemix-core</artifactId>
      <version>${servicemix-version}</version>
      <scope>provided</scope>
    </dependency>
  </dependencies>

  <build>
    <defaultGoal>install</defaultGoal>

    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <configuration>
          <source>1.5</source>
          <target>1.5</target>
        </configuration>
      </plugin>

      <!-- creates the JBI deployment unit -->
      <plugin>
        <groupId>org.apache.servicemix.tooling</groupId>
        <artifactId>jbi-maven-plugin</artifactId>
        <version>${servicemix-version}</version>
        <extensions>true</extensions>
      </plugin>
    </plugins>
  </build>
</project>

See Also

JCR Component

The jcr: component allows you to add nodes to a JCR (JSR-170) compliant content repository (e.g. Apache Jackrabbit ).

URI format

Usage

The repository element of the URI is used to look up the JCR Repository object in the Camel context registry.

If a message is sent to a producer endpoint created by this component:

Message properties

All message properties are converted to node properties, except for the org.apache.camel.component.jcr.node_name (you can refer to JcrComponent.NODE_NAME in your code), which is used to determine the node name.

Example

The snippet below will create a node named node under the /home/test node in the content repository. One additional attribute will be added to the node as well: my.contents.property will contain the body of the message being sent.

See Also

JDBC Component

The jdbc: component allows you to work with databases using JDBC queries and operations via QL text as the message payload

URI format

Options

NameDefault ValueDescription
readSize20,000The default maximum number of rows that can be read by a polling query

See Also

Jetty Component

The jetty: component provides HTTP based endpoints for consuming HTTP requests that arrive at an http endpoint.

URI format

Usage

You can only consume from endpoints generated by the Jetty component. Therefore it should only be used as input into your camel Routes. To issue HTTP requests against other HTTP endpoints you can use the HTTP Component

See Also

Jing Component

The Jing component uses the Jing Library to perform XML validation of the message body using either

Note that the MSV component can also support RelaxNG XML syntax.

URI format

Where rng means use the RelaxNG XML Syntax whereas rnc means use RelaxNG Compact Syntax. The following examples show possible URI values

ExampleDescription
rng:foo/bar.rngWill take the XML file foo/bar.rng on the classpath
rnc:http://foo.com/bar.rncWill use the RelaxNG Compact Syntax file from the URL http://foo.com/bar.rnc

Example

The following example shows how to configure a route from endpoint direct:start which then goes to one of two endpoints, either mock:valid or mock:invalid based on whether or not the XML matches the given RelaxNG Compact Syntax schema (which is supplied on the classpath).

<camelContext xmlns="http://activemq.apache.org/camel/schema/spring">
  <route>
    <from uri="direct:start"/>
    <try>
      <to uri="rnc:org/apache/camel/component/validator/jing/schema.rnc"/>
      <to uri="mock:valid"/>

      <catch>
        <exception>org.apache.camel.ValidationException</exception>
        <to uri="mock:invalid"/>
      </catch>
    </try>
  </route>
</camelContext>

See Also

JMS Component

The JMS component allows messages to be sent to a JMS Queue or Topic; or messages to be consumed from a JMS Queue or Topic. The implementation of the JMS Component uses Spring's JMS support for declarative transactions, using Spring's JmsTemplate for sending and a MessageListenerContainer for consuming.

URI format

So for example to send to queue FOO.BAR you would use

You can be completely specific if you wish via

If you want to send to a topic called Stocks.Prices then you would use

Notes

If you wish to use durable topic subscriptions, you need to specify both clientId and durableSubscriberName. Note that the value of the clientId must be unique and can only be used by a single JMS connection instance in your entire network. You may prefer to use Virtual Topics instead to avoid this limitation. More background on durable messaging here.

If you are using ActiveMQ

Note that the JMS component reuses Spring 2's JmsTemplate for sending messages. This is not ideal for use in a non-J2EE container and typically requires some caching JMS provider to avoid performance being lousy.

So if you intent to use Apache ActiveMQ as your Message Broker - which is a good choice as ActiveMQ rocks , then we recommend that you either

  • use the ActiveMQ component which is already configured to use ActiveMQ efficiently
  • use the PoolingConnectionFactory in ActiveMQ
For Consuming Messages cacheLevelName settings are vital!

If you are using Spring before 2.5.1 and Camel before 1.3.0 then you might want to set the cacheLevelName to be CACHE_CONSUMER for maximum performance.

Due to a bug in earlier Spring versions causing a lack of transactional integrity, previous versions of Camel and Camel versions from 1.3.0 onwwards when used with earlier Spring versions than 2.5.1 will default to use CACHE_CONNECTION. See the JIRAs CAMEL-163 and CAMEL-294.

Also if you are using XA or running in a J2EE container then you may want to set the cacheLevelName to be CACHE_NONE as we have seen using JBoss with TibCo EMS and JTA/XA you must disable caching.

Properties

You can configure lots of different properties on the JMS endpoint which map to properties on the JMSConfiguration POJO.

PropertyDefault ValueDescription
acceptMessagesWhileStoppingfalseShould the consumer accept messages while it is stopping
acknowledgementModeName"AUTO_ACKNOWLEDGE"The JMS acknowledgement name which is one of: TRANSACTED, CLIENT_ACKNOWLEDGE, AUTO_ACKNOWLEDGE, DUPS_OK_ACKNOWLEDGE
autoStartuptrueShould the consumer container auto-startup
cacheLevelName"CACHE_CONNECTION" but when SPR-3890 is fixed it will be "CACHE_CONSUMER"Sets the cache level name for the underlying JMS resources
clientIdnullSets the JMS client ID to use. Note that this value if specified must be unique and can only be used by a single JMS connection instance. Its typically only required for durable topic subscriptions. You may prefer to use Virtual Topics instead
concurrentConsumers1Specifies the default number of concurrent consumers
connectionFactorynullThe default JMS connection factory to use for the listenerConnectionFactory and templateConnectionFactory if neither are specified
deliveryPersistenttrueIs persistent delivery used by default?
disableReplyTofalseDo you want to ignore the JMSReplyTo header and so treat messages as InOnly by default and not send a reply back?
durableSubscriptionNamenullThe durable subscriber name for specifying durable topic subscriptions
exceptionListenernullThe JMS Exception Listener used to be notified of any underlying JMS exceptions
explicitQosEnabledfalseSet if the deliveryMode, priority or timeToLive should be used when sending messages
exposeListenerSessiontrueSet if the listener session should be exposed when consuming messages
idleTaskExecutionLimit1Specify the limit for idle executions of a receive task, not having received any message within its execution. If this limit is reached, the task will shut down and leave receiving to other executing tasks (in case of dynamic scheduling; see the "maxConcurrentConsumers" setting).
listenerConnectionFactorynullThe JMS connection factory used for consuming messages
maxConcurrentConsumers1Specifies the maximum number of concurrent consumers
maxMessagesPerTask1The number of messages per task
messageConverternullThe Spring Message Converter
messageIdEnabledtrueWhen sending, should message IDs be added
messageTimestampEnabledtrueShould timestamps be enabled by default on sending messages
priority-1Values of > 1 specify the message priority when sending, if the explicitQosEnabled property is specified
selectornullSets the JMS Selector which is an SQL 92 predicate used to apply to messages to filter them at the message broker. You may have to encode special characters such as = as %3D
receiveTimeoutnoneThe timeout when receiving messages
recoveryIntervalnoneThe recovery interval
serverSessionFactorynullThe JMS ServerSessionFactory if you wish to use ServerSessionFactory for consumption
subscriptionDurablefalseEnabled by default if you specify a durableSubscriberName and a clientId
taskExecutornullAllows you to specify a custom task executor for consuming messages
templateConnectionFactorynullThe JMS connection factory used for sending messages
timeToLivenullIs a time to live specified when sending messages
transactedfalseIs transacted mode used for sending/receiving messages?
transactionManagernullThe Spring transaction manager to use
transactionNamenullThe name of the transaction to use
transactionTimeoutnullThe timeout value of the transaction if using transacted mode
useVersion102falseShould the old JMS API be used

Configuring different JMS providers

You can configure your JMS provider inside the Spring XML as follows...

<camelContext id="camel" xmlns="http://activemq.apache.org/camel/schema/spring">
</camelContext>

<bean id="activemq" class="org.apache.camel.component.jms.JmsComponent">
  <property name="connectionFactory">
    <bean class="org.apache.activemq.ActiveMQConnectionFactory">
      <property name="brokerURL" value="vm://localhost?broker.persistent=false"/>
    </bean>
  </property>
</bean>

Basically you can configure as many JMS component instances as you wish and give them a unique name via the id attribute. The above example configures an 'activemq' component. You could do the same to configure MQSeries, TibCo, BEA, Sonic etc.

Once you have a named JMS component you can then refer to endpoints within that component using URIs. For example for the component name'activemq' you can then refer to destinations as activemq:[queue:|topic:]destinationName. So you could use the same approach for working with all other JMS providers.

This works by the SpringCamelContext lazily fetching components from the spring context for the scheme name you use for Endpoint URIs and having the Component resolve the endpoint URIs.

Using JNDI to find the ConnectionFactory

If you are using a J2EE container you might want to lookup in JNDI to find your ConnectionFactory rather than use the usual <bean> mechanism in spring. You can do this using Spring's factory bean or the new XML namespace. e.g.

See Also

JPA Component

The jpa: component allows you to work with databases using JPA (EJB 3 Persistence) such as for working with OpenJPA, Hibernate, TopLink to work with relational databases.

Sending to the endpoint

Sending POJOs to the JPA endpoint inserts entities into the database. The body of the message is assumed to be an entity bean (i.e. a POJO with an @Entity annotation on it).

If the body does not contain an entity bean then use a Message Translator in front of the endpoint to perform the necessary conversion first.

Consuming from the endpoint

Consuming messages removes (or updates) entities in the database. This allows you to use a database table as a logical queue, consumerse take messages from the queue and then delete/update them to logically remove them from the queue.

If you do not wish to delete the entity when it has been processed you can specify ?consumeDelete=false on the URI. This will result in the entity being processed each poll.

If you would rather perform some update on the entity to mark it as processed (such as to exclude it from a future query) then you can annotate a method with @Consumed which will be invoked on your entity bean when the entity bean is consumed.

URI format

For sending to the endpoint, the entityClassName is optional. If specified it is used to help use the [Type Conversion] to ensure the body is of the correct type.

For consuming the entityClassName is mandatory.

Options

NameDefault ValueDescription
persistenceUnitcamelthe JPA persistence unit used by default
consumeDeletetrueEnables / disables whether or not the entity is deleted after it is consumed

See Also

List Component

The List component provdes a simple BrowsableEndpoint which can be useful for testing, visualisation tools or debugging. The exchanges sent to the endpoint are all available to be browsed.

URI format

Where someName can be any string to uniquely identify the endpoint

See Also

Log Component

The log: component uses Jakarta Commons Logging to log message exchanges to the underlying logging system such as log4j.

URI format

Where loggingCategory is the name of the logging category to use and loggingLevel is the logging level such as DEBUG, INFO, WARN, ERROR - the default is INFO

See Also

Mail Component

The mail: component provides access to Email via Spring's Mail support and the underlying JavaMail system

URI format

which supports either POP, IMAP or SMTP underlying protocols.

PropertyDescription
hostthe host name or IP address to connect to
portthe TCP port number to connect on
user-infothe user name on the email server
passwordthe users password to use

See Also

MINA Component

The mina: component is a transport for working with Apache MINA

URI format

From Camel 1.3 onwards you can specify a codec in the Registry using the codec option. If you are using TCP and no codec is specified then the textline flag is used to determine if text line based codec or object serialization should be used instead.

For UDP/Multicast if no codec is specified the default uses a basic ByteBuffer based codec.

Multicast also has a shorthand notation mcast.

The VM protocol is used as a direct forwarding mechanism in the same JVM. See the MINA VM-Pipe API documentation for details.

A MinaProducer has a default timeout value of 30 seconds, while it waits for a response from the remote server.

In normal usage Camel-mina only supports marshalling the body content - message headers and exchange properties will not be sent.
However the option transferExchange does allow to transfer the exchange itself over the wire. See options below.

Options

NameDefault ValueDescription
codecnullAs of 1.3 or later you can refer to a named ProtocolCodecFactory instance in your Registry such as your Spring ApplicationContext which is then used for the marshalling
textlinenullOnly used for TCP. If no codec is specified then you can use this flag in 1.3 or later to indicate a text line based codec; if not specified or the value is false then Object Serialization is assumed over TCP.
syncfalseAs of 1.3 or later you can configure the exchange pattern to be either InOnly (default) or InOut. Setting sync=true means a synchronous exchange (InOut), where the client can read the response from MINA (The exchange out message).
lazySessionCreationfalseAs of 1.3 or later session can be lazy created to avoid exceptions if the remote server is not up and running when the Camel producer is started.
timeout30000As of 1.3 or later you can configure the timeout while waiting for a response from a remote server. The timeout unit is in millis, so 60000 is 60 seconds. The timeout is only used for MinaProducer.
encodingJVM DefaultAs of 1.3 or later you can configure the encoding (is a charset name) to use for the TCP textline codec and the UDP protocol. If not provided Camel will use the JVM default Charset.
transferExchangefalseOnly used for TCP. As of 1.3 or later you can transfer the exchange over the wire instead of just the body. The following fields is transfered: in body, out body, in headers, out headers, exchange properties, exchange exception.
minaLoggerfalseAs of 1.3 or later you can enable Apache MINA logging filter. Apache MINA uses slf4j logging at INFO level to log all input and output.

See Also

Mock Component

Testing of distributed and asynchronous processing is notoriously difficult. The Mock, Test and DataSet endpoints work great with the Spring Testing framework to simplify your unit and integration testing using Enterprise Integration Patterns and Camel's large range of Components together with the powerful Mock and Test testing endpoints.

The Mock component provides a powerful declarative testing mechanism which is similar to jMock in that it allows declarative expectations to be created on any Mock endpoint before a test begins. Then the test is ran which typically fires messages to one or more endpoints and finally the expectations can be asserted in a test case to ensure the system worked as expected.

This allows you to test various things like

Note that there is also the Test endpoint which is-a Mock endpoint but which also uses a second endpoint to provide the list of expected message bodies and automatically sets up the Mock endpoint assertions. i.e. its a Mock endpoint which automatically sets up its assertions from some sample messages in a File or database for example.

URI format

Where someName can be any string to uniquely identify the endpoint

Simple Example

Here's a simple example of MockEndpoint in use. First the endpoint is resolved on the context. Then we set an expectation, then after the test has run we assert our expectations are met.

You typically always call the assertIsSatisfied() method to test that the expectations were met after running a test.

Setting expectations

You can see from the javadoc of MockEndpoint the various helper methods you can use to set expectations. The main methods available are as follows

MethodDescription
expectedMessageCount(int) to define the expected message count on the endpoint
expectedMinimumMessageCount(int) to define the minimum number of expected messages on the endpoint
expectedBodiesReceived(...) to define the expected bodies that should be received (in order)
expectsAscending(Expression) to add an expectation that messages are received in order using the given Expression to compare messages
expectsDescending(Expression) to add an expectation that messages are received in order using the given Expression to compare messages
expectsNoDuplicates(Expression) to add an expectation that no duplicate messages are received; using an Expression to calculate a unique identifier for each message. This could be something like the JMSMessageID if using JMS, or some unique reference number within the message.

Here's another example

resultEndpoint.expectedBodiesReceived("firstMessageBody", "secondMessageBody", "thirdMessageBody");

Adding expectations to specific messages

In addition you can use the message(int messageIndex) method to add assertions about a specific message that is received.

For example to add expectations of the headers or body of the first message (using zero based indexing like java.util.List), you can use this code

resultEndpoint.message(0).header("foo").isEqualTo("bar");

There are some examples of the Mock endpoint in use in the camel-core processor tests.

A Spring Example

First here's the spring.xml file

<camelContext xmlns="http://activemq.apache.org/camel/schema/spring">
  <route>
    <from uri="file:src/test/data?noop=true"/>
    <filter>
      <xpath>/person/city = 'London'</xpath>
      <to uri="mock:matched"/>
    </filter>
  </route>
</camelContext>

<bean id="myBean" class="org.apache.camel.spring.mock.MyAssertions" scope="singleton"/>

As you can see it defines a simple routing rule which consumes messages from the local src/test/data directory. The noop flag just means not to delete or move the file after its been processed.

Also note we instantiate a bean called myBean, here is the source of the MyAssertions bean.

public class MyAssertions implements InitializingBean {
    @EndpointInject(uri = "mock:matched")
    private MockEndpoint matched;

    @EndpointInject(uri = "mock:notMatched")
    private MockEndpoint notMatched;

    public void afterPropertiesSet() throws Exception {
        // lets add some expectations
        matched.expectedMessageCount(1);
        notMatched.expectedMessageCount(0);
    }

    public void assertEndpointsValid() throws Exception {
        // now lets perform some assertions that the test worked as we expect
        Assert.assertNotNull("Should have a matched endpoint", matched);
        Assert.assertNotNull("Should have a notMatched endpoint", notMatched);
        MockEndpoint.assertIsSatisfied(matched, notMatched);
    }
}

The bean is injected with a bunch of Mock endpoints using the @EndpointInject annotation, it then sets a bunch of expectations on startup (using Spring's InitializingBean interface and afterPropertiesSet() method) before the CamelContext starts up.

Then in our test case (which could be JUnit or TesNG) we lookup myBean in Spring (or have it injected into our test) and then invoke the assertEndpointsValid() method on it to verify that the mock endpoints have their assertions met. You could then inspect the message exchanges that were delivered to any of the endpoints using the getReceivedExchanges() method on the Mock endpoint and perform further assertions or debug logging.

Here is the actual JUnit test case we use.

See Also

MSV Component

The MSV component performs XML validation of the message body using the MSV Library using any of the XML schema languages supported such as XML Schema or RelaxNG XML Syntax.

Note that the Jing component also supports RelaxNG Compact Syntax

URI format

Where someLocalOrRemoteResource is some URL to a local resource on the classpath or a full URL to a remote resource or resource on the file system. For example

Example

The following example shows how to configure a route from endpoint direct:start which then goes to one of two endpoints, either mock:valid or mock:invalid based on whether or not the XML matches the given RelaxNG XML Schema (which is supplied on the classpath).

<camelContext xmlns="http://activemq.apache.org/camel/schema/spring">
  <route>
    <from uri="direct:start"/>
    <try>
      <to uri="msv:org/apache/camel/component/validator/msv/schema.rng"/>
      <to uri="mock:valid"/>

      <catch>
        <exception>org.apache.camel.ValidationException</exception>
        <to uri="mock:invalid"/>
      </catch>
    </try>
  </route>
</camelContext>

See Also

Pojo Component

The pojo: component is now just an alias for the Bean component.

See Also

Quartz Component

The quartz: component provides a scheduled delivery of messages using the Quartz scheduler.
Each endpoint represents a different timer (in Quartz terms, a Trigger and JobDetail).

URI format

You can configure the Trigger and JobDetail using the parameters

PropertyDescription
trigger.repeatCountHow many times should the timer repeat for?
trigger.repeatIntervalThe amount of time in milliseconds between repeated triggers
job.nameSets the name of the job

For example the following routing rule will fire 2 timer events to the endpoint mock:results

Using Cron Triggers

Quartz supports Cron-like expressions for specifying timers in a handy format. You can use these expressions in the URI; though to preserve valid URI encoding we allow / to be used instead of spaces and $ to be used instead of ?.

For example the following will fire a message at 12pm (noon) every day

from("quartz://myGroup/myTimerName/0/0/12/*/*/$").to("activemq:Totally.Rocks");

which is equivalent to using the cron expression

0 0 12 * * ?

The following table shows the URI character encodings we use to preserve valid URI syntax

URI CharacterCron character
'/'' '
'$''?'

See Also

Queue Component

Deprecated

To avoid confusion with JMS queues, this component is now deprecated in 1.1 onwards. Please use the SEDA component instead

The queue: component provides asynchronous SEDA behaviour so that messages are exchanged on a BlockingQueue and consumers are invoked in a seperate thread pool to the producer.

Note that queues are only visible within a single CamelContext. If you want to communicate across CamelContext instances such as to communicate across web applications, see the VM component.

Note also that this component has nothing to do with JMS, if you want a distributed SEA then try using either JMS or ActiveMQ or even MINA

URI format

Where someName can be any string to uniquely identify the endpoint within the current CamelContext

See Also

RMI Component

The rmi: component bind the PojoExchanges to the RMI protocol (JRMP).

Since this binding is just using RMI, normal RMI rules still apply in regards to what the methods can be used over it. This component only supports PojoExchanges that carry a method invocation that is part of an interface that extends the Remote interface. All parameters in the method should be either Serializable or Remote objects too.

URI format

For example:

Using

To call out to an existing RMI service registered in an RMI registry, create a Route similar to:

To bind an existing camel processor or service in an RMI registry, create a Route like:

Notice that when binding an inbound RMI endpoint, the Remote interfaces exposed must be specified.

See Also

SEDA Component

The seda: component provides asynchronous SEDA behaviour so that messages are exchanged on a BlockingQueue and consumers are invoked in a seperate thread to the producer. Be aware that adding a thread pool to a seda
endpoint by doing something like: from("seda:stageName").thread(5).process(...) can wind up with two BlockQueues. One from seda endpoint and one from the workqueue of the thread pool which may not be what you want. Instead, you might want to consider configuring a direct endpoint with a thread pool which can process messages both synchronously and asynchronously. For example, from(direct:stageName").thread(5).process(..).

Note that queues are only visible within a single CamelContext. If you want to communicate across CamelContext instances such as to communicate across web applications, see the VM component.

This component does not implement any kind of persistence or recovery if the VM termininates while messages are yet to be processed. If you need persistence, reliability or distributed SEDA then try using either JMS or ActiveMQ

URI format

Where someName can be any string to uniquely identify the endpoint within the current CamelContext

URI Options

NameDescription
sizeThe maximum size of the SEDA queue

See Also

String Template

The string-template: component allows you to process a message using a String Template. This can be ideal when using Templating to generate respopnses for requests.

URI format

Where templateName is the classpath-local URI of the template to invoke; or the complete URL of the remote template.

For example you could use something like

To use a string template to forumulate a response for a message

Options

NameDefault ValueDescription

See Also

|

Test Component

Testing of distributed and asynchronous processing is notoriously difficult. The Mock, Test and DataSet endpoints work great with the Spring Testing framework to simplify your unit and integration testing using Enterprise Integration Patterns and Camel's large range of Components together with the powerful Mock and Test testing endpoints.

The Test component extends the Mock component to support pulling messages from another endpoint on startup to set the expected message bodies on the underlying Mock endpoint.

i.e. you use the test endpoint in a route and messages arriving on it will be implicitly compared to some expected messages extracted from some other location.

So you can use for example an expected set of message bodies as files. This will then setup a properly configured Mock endpoint which is only valid if the received messages match the number of expected messages and their message payloads are equal.

URI format

Where expectedMessagesEndpointUri refers to some other Component URI where the expected message bodies are pulled from before starting the test.

Example

For example you could write a test case as follows

If your test then invokes the MockEndpoint.assertIsSatisfied(camelContext) method then your test case will perform the necessary assertions.

Here is a real example test case using Mock and Spring along with its Spring XML.

To see how you can set other expectations on the test endpoint, see the Mock component.

See Also

Timer Component

The timer: component is used to generate message exchanges when a timer fires You can only consume events from this endpoint.

URI format

Where options is a query string that can specify any of the following parameters:

NameDefault ValueDescription
namenullThe name of the Timer object which is created and shared across endpoints. So if you use the same name for all your timer endpoints then only one Timer object & thread will be used
timeÊThe date/time that the (first) event should be generated.
period-1If set to greater than 0, then generate periodic events every period milliseconds
delay-1The number of milliseconds to wait before the first event is generated. Should not be used in conjunction with the time parameter.
fixedRatefalseEvents take place at approximately regular intervals, separated by the specified period.
daemontrueShould the thread associated with the timer endpoint be run as a daemon.

Using

To setup a route that generates an event every 60 seconds:

The above route will generate an event then invoke the someMethodName on the bean called myBean in the Registry such as JNDI or Spring.

See Also

Validation Component

The Validation component performs XML validation of the message body using the JAXP Validation API using any of the supported XML schema languages, which defaults to XML Schema

Note that the Jing component also supports the following schema languages which are useful

The MSV component also supports RelaxNG XML Syntax.

URI format

Where someLocalOrRemoteResource is some URL to a local resource on the classpath or a full URL to a remote resource or resource on the file system which contains the XSD to validate against. For example

Example

The following example shows how to configure a route from endpoint direct:start which then goes to one of two endpoints, either mock:valid or mock:invalid based on whether or not the XML matches the given schema (which is supplied on the classpath).

<camelContext xmlns="http://activemq.apache.org/camel/schema/spring">
  <route>
    <from uri="direct:start"/>
    <try>
      <to uri="validator:org/apache/camel/component/validator/schema.xsd"/>
      <to uri="mock:valid"/>

      <catch>
        <exception>org.apache.camel.ValidationException</exception>
        <to uri="mock:invalid"/>
      </catch>
    </try>
  </route>
</camelContext>

See Also

Velocity

The velocity: component allows you to process a message using an Apache Velocity template. This can be ideal when using Templating to generate respopnses for requests.

URI format

Where templateName is the classpath-local URI of the template to invoke; or the complete URL of the remote template.

For example you could use something like

To use a velocity template to forumulate a response for a message for InOut message exchanges (where there is a JMSReplyTo header).

If you want to use InOnly and consume the message and send it to another destination you could use

Options

NameDefault ValueDescription

See Also

|

VM Component

The vm: component provides asynchronous SEDA behaviour so that messages are exchanged on a BlockingQueue and consumers are invoked in a seperate thread pool to the producer.

This component differs from the Queue component in that VM supports communcation across CamelContext instances so you can use this mechanism to communicate across web applications, provided that the camel-core.jar is on the system/boot classpath

URI format

Where someName can be any string to uniquely identify the endpoint within the JVM (or at least within the classloader which loaded the camel-core.jar)

See Also

XMPP Component

The xmpp: component implements an XMPP (Jabber) transport.

URI format

The component supports both room based and private person-person conversations

See Also

XQuery

The xquery: component allows you to process a message using an XQuery template. This can be ideal when using Templating to generate respopnses for requests.

URI format

Where templateName is the classpath-local URI of the template to invoke; or the complete URL of the remote template.

For example you could use something like

To use a xquery template to forumulate a response for a message for InOut message exchanges (where there is a JMSReplyTo header).

If you want to use InOnly and consume the message and send it to another destination you could use

Options

NameDefault ValueDescription

See Also

|

XSLT

The xslt: component allows you to process a message using an XSLT template. This can be ideal when using Templating to generate respopnses for requests.

URI format

Where templateName is the classpath-local URI of the template to invoke; or the complete URL of the remote template. Refer to the Spring Documentation for more detail of the URI syntax

Here are some example URIs

URIDescription
xslt:com/acme/mytransform.xsl
refers to the file com/acme/mytransform.xsl on the classpath
xslt:file:///foo/bar.xsl
refers to the file /foo/bar.xsl
xslt:http://acme.com/cheese/foo.xsl
refers to the remote http resource

Using XSLT endpoints

For example you could use something like

To use a xslt template to forumulate a response for a message for InOut message exchanges (where there is a JMSReplyTo header).

If you want to use InOnly and consume the message and send it to another destination you could use

Spring XML versions

To use the above examples in Spring XML you would use something like

There is a test case along with its Spring XML if you want a concrete example.

Options

NameDefault ValueDescription

See Also

|