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.

JNDI

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.

Without JNDI

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();
    }