This package contains one public class which is a DataSource
implementation which provides a database connection pool. Below are a couple
of usage examples. One shows deployment into a JNDI system. The other
is a simple example initializing the pool using common java code.
Most J2EE containers will provide some way of deploying resources into JNDI. The method will vary among containers, but once the resource is available via JNDI, the application can access the resource in a container independent manner. The following example shows deployment into catalina.
In server.xml, the following would be added to the <Context> for your webapp:
<Resource name="jdbc/bookstore" auth="Container"
type="org.apache.commons.dbcp.jdbc2pool.Jdbc2PoolDataSource"/>
<ResourceParams name="jdbc/bookstore">
<parameter>
<name>factory</name>
<value>org.apache.commons.dbcp.jdbc2pool.Jdbc2PoolDataSource</value>
</parameter>
<parameter>
<name>dataSourceName</name><value>java:comp/env/jdbc/bookstoreCPDS</value>
</parameter>
<parameter>
<name>defaultMaxActive</name><value>30</value>
</parameter>
</ResourceParams>
In web.xml. Note that elements must be given in the order of the dtd described in the servlet specification:
<resource-ref>
<description>
Resource reference to a factory for java.sql.Connection
instances that may be used for talking to a particular
database that is configured in the server.xml file.
</description>
<res-ref-name>
jdbc/bookstore
</res-ref-name>
<res-type>
org.apache.commons.dbcp.jdbc2pool.Jdbc2PoolDataSource
</res-type>
<res-auth>
Container
</res-auth>
</resource-ref>
Catalina deploys all objects configured similarly to above within the
java:comp/env namespace. So the JNDI path given for
the dataSourceName parameter is valid for a
ConnectionPoolDataSource
that is deployed as given in the
cpdsadapter example
The DataSource
is now available to the application as shown
below:
Context ctx = new InitialContext();
DataSource ds = (DataSource)
ctx.lookup("java:comp/env/jdbc/bookstore");
Connection con = null;
try
{
con = ds.getConnection();
...
use the connection
...
}
finally
{
if (con != null)
con.close();
}
The reference to the DataSource
could be maintained, for
multiple getConnection() requests. Or the DataSource
can be
looked up in different parts of the application code. Jdbc2PoolDataSource
will maintain the state of the pool between different lookups. This
behavior may be different
among in other implementations. It is in contrast to the behavior of
{@link org.apache.commons.dbcp.BasicDataSource}, where two lookups of a pool set to a maximum of
100 connections will lead to two independent sets of connections for a total
of 200. With Jdbc2PoolDataSource, you are expected to deploy different
instances under different names, if you wish to have independent sets of
connections.
Connection pooling is useful in applications regardless of whether they run in a J2EE environment and Jdbc2PoolDataSource can be used within a simpler environment. The example below shows DriverAdapterCPDS used as the source, though any CPDS is applicable.
public class Pool
{
public static DataSource ds;
static
{
DriverAdapterCPDS cpds = new DriverAdapterCPDS();
cpds.setDriver("org.gjt.mm.mysql.Driver");
cpds.setUrl("jdbc:mysql://localhost:3306/bookstore");
cpds.setUser("foo");
cpds.setPassword(null);
Jdbc2PoolDataSource tds = new Jdbc2PoolDataSource();
tds.setConnectionPoolDataSource(cpds);
tds.setDefaultMaxActive(10);
tds.setDefaultMaxWait(50);
ds = tds;
}
}
This class can then be used wherever a connection is needed:
Connection con = null;
try
{
con = Pool.ds.getConnection();
...
use the connection
...
}
finally
{
if (con != null)
con.close();
}