# Package org.apache.commons.dbcp2.datasources

package org.apache.commons.dbcp2.datasources

This package contains two DataSources: `PerUserPoolDataSource` and `SharedPoolDataSource` which provide 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 standard 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 tomcat (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.dbcp2.datasources.PerUserPoolPoolDataSource"/>
       <ResourceParams name="jdbc/bookstore">
         <parameter>
           <name>factory</name>
           <value>org.apache.commons.dbcp2.datasources.PerUserPoolDataSourceFactory</value>
         </parameter>
         <parameter>
           <name>dataSourceName</name><value>java:comp/env/jdbc/bookstoreCPDS</value>
         </parameter>
         <parameter>
           <name>defaultMaxTotal</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.dbcp2.datasources.PerUserPoolDataSource
       </res-type>
       <res-auth>
         Container
       </res-auth>
     </resource-ref>

Apache Tomcat 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. `PerUserPoolDataSourceFactory` and `SharedPoolDataSourceFactory` will maintain the state of the pool between different lookups. This behavior may be different in other implementations.

## Without JNDI

Connection pooling is useful in applications regardless of whether they run in a J2EE environment and a `DataSource` can be used within a simpler environment. The example below shows SharedPoolDataSource using DriverAdapterCPDS as the back end source, though any CPDS is applicable.

     public class Pool {

         private 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);

             SharedPoolDataSource tds = new SharedPoolDataSource();
             tds.setConnectionPoolDataSource(cpds);
             tds.setMaxTotal(10);
             tds.setMaxWaitMillis(50);

             ds = tds;
         }

         public static getConnection() {
             return ds.getConnection();
         }
     }

This class can then be used wherever a connection is needed:

         Connection con = null;
         try {
             con = Pool.getConnection();
             ...
             use the connection
             ...
         } finally {
             if (con != null) {
                 con.close();
             }
         }

- Related Packages
  Package
  Description
  org.apache.commons.dbcp2
  Database Connection Pool API.
  org.apache.commons.dbcp2.cpdsadapter
  This package contains one public class which is a `ConnectionPoolDataSource` (CPDS) implementation that can be used to adapt older `Driver` based JDBC implementations.
  org.apache.commons.dbcp2.managed
  This package provides support for pooling of ManagedConnections.
- Classes
  Class
  Description
  InstanceKeyDataSource
  The base class for `SharedPoolDataSource` and `PerUserPoolDataSource`.
  PerUserPoolDataSource
  A pooling `DataSource` appropriate for deployment within J2EE environment.
  PerUserPoolDataSourceFactory
  A JNDI ObjectFactory which creates `SharedPoolDataSource`s
  SharedPoolDataSource
  A pooling `DataSource` appropriate for deployment within J2EE environment.
  SharedPoolDataSourceFactory
  A JNDI ObjectFactory which creates `SharedPoolDataSource`s