Servlet Component

Available as of Camel version 2.0

The servlet: component provides HTTP based endpoints for consuming HTTP requests that arrive at a HTTP endpoint that is bound to a published Servlet.

Maven users will need to add the following dependency to their pom.xml for this component:

<dependency>
    <groupId>org.apache.camel</groupId>
    <artifactId>camel-servlet</artifactId>
    <version>x.x.x</version>
    <\!-\- use the same version as your Camel core version \-->
</dependency>

INFO: Stream. Servlet is stream based, which means the input it receives is submitted to Camel as a stream. That means you will only be able to read the content of the stream once. If you find a situation where the message body appears to be empty or you need to access the data multiple times (eg: doing multicasting, or redelivery error handling) you should use Stream caching or convert the message body to a String which is safe to be read multiple times.

URI format

servlet://relative_path[?options]

You can append query options to the URI in the following format, ?option=value&option=value&…​

Options

The Servlet component supports 8 options which are listed below.

Name Description Default Type

servletName (consumer)

Default name of servlet to use. The default name is CamelServlet.

String

httpRegistry (consumer)

To use a custom org.apache.camel.component.servlet.HttpRegistry.

HttpRegistry

attachmentMultipart Binding (consumer)

Whether to automatic bind multipart/form-data as attachments on the Camel Exchange. The options attachmentMultipartBinding=true and disableStreamCache=false cannot work together. Remove disableStreamCache to use AttachmentMultipartBinding. This is turn off by default as this may require servlet specific configuration to enable this when using Servlet’s.

false

boolean

httpBinding (advanced)

To use a custom HttpBinding to control the mapping between Camel message and HttpClient.

HttpBinding

httpConfiguration (advanced)

To use the shared HttpConfiguration as base configuration.

HttpConfiguration

allowJavaSerialized Object (advanced)

Whether to allow java serialization when a request uses context-type=application/x-java-serialized-object. This is by default turned off. If you enable this then be aware that Java will deserialize the incoming data from the request to Java and that can be a potential security risk.

false

boolean

headerFilterStrategy (filter)

To use a custom org.apache.camel.spi.HeaderFilterStrategy to filter header to and from Camel message.

HeaderFilterStrategy

resolveProperty Placeholders (advanced)

Whether the component should resolve property placeholders on itself when starting. Only properties which are of String type can use property placeholders.

true

boolean

The Servlet endpoint is configured using URI syntax:

servlet:contextPath

with the following path and query parameters:

Path Parameters (1 parameters):

Name Description Default Type

contextPath

Required The context-path to use

String

Query Parameters (21 parameters):

Name Description Default Type

disableStreamCache (common)

Determines whether or not the raw input stream from Servlet is cached or not (Camel will read the stream into a in memory/overflow to file Stream caching) cache. By default Camel will cache the Servlet input stream to support reading it multiple times to ensure it Camel can retrieve all data from the stream. However you can set this option to true when you for example need to access the raw stream such as streaming it directly to a file or other persistent store. DefaultHttpBinding will copy the request input stream into a stream cache and put it into message body if this option is false to support reading the stream multiple times. If you use Servlet to bridge/proxy an endpoint then consider enabling this option to improve performance in case you do not need to read the message payload multiple times. The http/http4 producer will by default cache the response body stream. If setting this option to true then the producers will not cache the response body stream but use the response stream as-is as the message body.

false

boolean

headerFilterStrategy (common)

To use a custom HeaderFilterStrategy to filter header to and from Camel message.

HeaderFilterStrategy

httpBinding (common)

To use a custom HttpBinding to control the mapping between Camel message and HttpClient.

HttpBinding

async (consumer)

Configure the consumer to work in async mode

false

boolean

bridgeErrorHandler (consumer)

Allows for bridging the consumer to the Camel routing Error Handler which mean any exceptions occurred while the consumer is trying to pickup incoming messages or the likes will now be processed as a message and handled by the routing Error Handler. By default the consumer will use the org.apache.camel.spi.ExceptionHandler to deal with exceptions that will be logged at WARN or ERROR level and ignored.

false

boolean

chunked (consumer)

If this option is false the Servlet will disable the HTTP streaming and set the content-length header on the response

true

boolean

httpMethodRestrict (consumer)

Used to only allow consuming if the HttpMethod matches such as GET/POST/PUT etc. Multiple methods can be specified separated by comma.

String

matchOnUriPrefix (consumer)

Whether or not the consumer should try to find a target consumer by matching the URI prefix if no exact match is found.

false

boolean

responseBufferSize (consumer)

To use a custom buffer size on the javax.servlet.ServletResponse.

Integer

servletName (consumer)

Name of the servlet to use

CamelServlet

String

transferException (consumer)

If enabled and an Exchange failed processing on the consumer side and if the caused Exception was send back serialized in the response as a application/x-java-serialized-object content type. On the producer side the exception will be deserialized and thrown as is instead of the HttpOperationFailedException. The caused exception is required to be serialized. This is by default turned off. If you enable this then be aware that Java will deserialize the incoming data from the request to Java and that can be a potential security risk.

false

boolean

attachmentMultipartBinding (consumer)

Whether to automatic bind multipart/form-data as attachments on the Camel Exchange. The options attachmentMultipartBinding=true and disableStreamCache=false cannot work together. Remove disableStreamCache to use AttachmentMultipartBinding. This is turn off by default as this may require servlet specific configuration to enable this when using Servlet’s.

false

boolean

eagerCheckContentAvailable (consumer)

Whether to eager check whether the HTTP requests has content if the content-length header is 0 or not present. This can be turned on in case HTTP clients do not send streamed data.

false

boolean

exceptionHandler (consumer)

To let the consumer use a custom ExceptionHandler. Notice if the option bridgeErrorHandler is enabled then this options is not in use. By default the consumer will deal with exceptions that will be logged at WARN or ERROR level and ignored.

ExceptionHandler

exchangePattern (consumer)

Sets the exchange pattern when the consumer creates an exchange.

ExchangePattern

optionsEnabled (consumer)

Specifies whether to enable HTTP OPTIONS for this Servlet consumer. By default OPTIONS is turned off.

false

boolean

traceEnabled (consumer)

Specifies whether to enable HTTP TRACE for this Servlet consumer. By default TRACE is turned off.

false

boolean

mapHttpMessageBody (advanced)

If this option is true then IN exchange Body of the exchange will be mapped to HTTP body. Setting this to false will avoid the HTTP mapping.

true

boolean

mapHttpMessageFormUrl EncodedBody (advanced)

If this option is true then IN exchange Form Encoded body of the exchange will be mapped to HTTP. Setting this to false will avoid the HTTP Form Encoded body mapping.

true

boolean

mapHttpMessageHeaders (advanced)

If this option is true then IN exchange Headers of the exchange will be mapped to HTTP headers. Setting this to false will avoid the HTTP Headers mapping.

true

boolean

synchronous (advanced)

Sets whether synchronous processing should be strictly used or Camel is allowed to use asynchronous processing (if supported).

false

boolean

Message Headers

Camel will apply the same Message Headers as the HTTP component.

Camel will also populate all request.parameter and request.headers. For example, if a client request has the URL, http://myserver/myserver?orderid=123, the exchange will contain a header named orderid with the value 123.

Usage

You can consume only from endpoints generated by the Servlet component. Therefore, it should be used only as input into your Camel routes. To issue HTTP requests against other HTTP endpoints, use the HTTP Component

Putting Camel JARs in the app server boot classpath

If you put the Camel JARs such as camel-core, camel-servlet, etc. in the boot classpath of your application server (eg usually in its lib directory), then mind that the servlet mapping list is now shared between multiple deployed Camel application in the app server.

Mind that putting Camel JARs in the boot classpath of the application server is generally not best practice!

So in those situations you must define a custom and unique servlet name in each of your Camel application, eg in the web.xml define:

<servlet>
  <servlet-name>MyServlet</servlet-name>
  <servlet-class>org.apache.camel.component.servlet.CamelHttpTransportServlet</servlet-class>
  <load-on-startup>1</load-on-startup>
</servlet>

<servlet-mapping>
  <servlet-name>MyServlet</servlet-name>
  <url-pattern>/*</url-pattern>
</servlet-mapping>

And in your Camel endpoints then include the servlet name as well

<route>
  <from uri="servlet://foo?servletName=MyServlet"/>
  ...
</route>

From Camel 2.11 onwards Camel will detect this duplicate and fail to start the application. You can control to ignore this duplicate by setting the servlet init-parameter ignoreDuplicateServletName to true as follows:

  <servlet>
    <servlet-name>CamelServlet</servlet-name>
    <display-name>Camel Http Transport Servlet</display-name>
    <servlet-class>org.apache.camel.component.servlet.CamelHttpTransportServlet</servlet-class>
    <init-param>
      <param-name>ignoreDuplicateServletName</param-name>
      <param-value>true</param-value>
    </init-param>
  </servlet>

But its strongly advised to use unique servlet-name for each Camel application to avoid this duplication clash, as well any unforeseen side-effects.

Sample

INFO: From Camel 2.7 onwards it’s easier to use Servlet in Spring web applications. See Servlet Tomcat Example for details.

In this sample, we define a route that exposes a HTTP service at http://localhost:8080/camel/services/hello.
First, you need to publish the CamelHttpTransportServlet through the normal Web Container, or OSGi Service.
Use the Web.xml file to publish the CamelHttpTransportServlet as follows:

Then you can define your route as follows:

Note
Specify the relative path for camel-servlet endpoint Since we are binding the Http transport with a published servlet, and we don’t know the servlet’s application context path, the camel-servlet endpoint uses the relative path to specify the endpoint’s URL. A client can access the camel-servlet endpoint through the servlet publish address: ("http://localhost:8080/camel/services") + RELATIVE_PATH("/hello").

Sample when using Spring 3.x

Sample when using Spring 2.x

When using the Servlet component in a Camel/Spring application it’s often required to load the Spring ApplicationContext after the Servlet component has started. This can be accomplished by using Spring’s ContextLoaderServlet instead of ContextLoaderListener. In that case you’ll need to start ContextLoaderServlet after CamelHttpTransportServlet like this:

<web-app>
  <servlet>
        <servlet-name>CamelServlet</servlet-name>
        <servlet-class>
            org.apache.camel.component.servlet.CamelHttpTransportServlet
        </servlet-class>
        <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet>
        <servlet-name>SpringApplicationContext</servlet-name>
        <servlet-class>
            org.springframework.web.context.ContextLoaderServlet
        </servlet-class>
        <load-on-startup>2</load-on-startup>
  </servlet>
<web-app>

Sample when using OSGi

From Camel 2.6.0, you can publish the CamelHttpTransportServlet as an OSGi service with help of SpringDM like this.

Then use this service in your camel route like this:

For versions prior to Camel 2.6 you can use an Activator to publish the CamelHttpTransportServlet on the OSGi platform

Usage with Spring-Boot

From Camel 2.19.0 onwards, the camel-servlet-starter library binds automatically all the rest endpoints under the "/camel/*" context path. The following table summarizes the additional configuration properties available in the camel-servlet-starter library. The automatic mapping of the Camel servlet can also be disabled.

Spring-Boot Property Default Description

camel.component.servlet.mapping.enabled

true

Enables the automatic mapping of the servlet component into the Spring web context

camel.component.servlet.mapping.context-path

/camel/*

Context path used by the servlet component for automatic mapping

camel.component.servlet.mapping.servlet-name

CamelServlet

The name of the Camel servlet