How is Connection Pooler Found

Question

In Tomcat (say) one defines a resource like
<Resource name="jdbc/myjdbc" type="javax.sql.DataSource"/>...
(Note that DataSource is an interface, not a class.)
In the code we then just say
envCtx=InitialContext().lookup("java:comp/env");
DataSource ds = envCtx.lookup("jdbc/myjdbc");
But how on earth does JNDI/Tomcat know which factory to use create a DataSource? How does it know to use DBCP for this connection, and not some other pool? How could it without having weird hooks into JINDI?
Anthony

Answer 1

OK so there is an additional factory parameter that presumably has a default value of dbcp.
<Resource name="jdbc/testdbfPool1" auth="Container" type="javax.sql.DataSource"/>     
     <ResourceParams name="jdbc/testDBFPool1">
          <parameter>
               <name>factory</name>
               <value>org.apache.commons.dbcp.BasicDataSourceFactory</value>
          </parameter>
          <parameter>
               <name>driverClassName</name>
               <value>com.hxtt.sql.dbf.DBFDriver</value>
          </parameter>     
          <parameter>
               <name>url</name>     
               <value>jdbc:dbf:///d:/dbffiles</value>
          </parameter>
Thanks for the reply. I was surprised not to see something on the jdbc resource definition, forgot about defaults.
Anthony