Database Connection Pool API.
Overview in Dialog FormQ: How do I use the DBCP package?
A: There are two primary ways to access the DBCP pool, as a {@link java.sql.Driver Driver}, or as a {@link javax.sql.DataSource DataSource}. You'll want to create an instance of {@link org.apache.commons.dbcp.PoolingDriver} or {@link org.apache.commons.dbcp.PoolingDataSource}. When using one of these interfaces, you can just use your JDBC objects the way you normally would. Closing a {@link java.sql.Connection} will simply return it to its pool.
Q: But {@link org.apache.commons.dbcp.PoolingDriver PoolingDriver} and {@link org.apache.commons.dbcp.PoolingDataSource PoolingDataSource} both expect an {@link org.apache.commons.pool.ObjectPool ObjectPool} as an input. Where do I get one of those?
A: The {@link org.apache.commons.pool.ObjectPool ObjectPool} interface is defined in the {@link org.apache.commons.pool} package (Commons-Pool). The {@link org.apache.commons.pool.impl} package has a couple of implementations, and you can always create your own.
Q: Ok, I've found an {@link org.apache.commons.pool.ObjectPool ObjectPool} implementation that I think suits my connection pooling needs. But it wants a {@link org.apache.commons.pool.PoolableObjectFactory PoolableObjectFactory}. What should I use for that?
A: The DBCP package provides a class for this purpose. It's called {@link org.apache.commons.dbcp.PoolableConnectionFactory}. It implements the factory and lifecycle methods of {@link org.apache.commons.pool.PoolableObjectFactory} for {@link java.sql.Connection}s. But it doesn't create the actual database {@link java.sql.Connection}s itself, if uses a {@link org.apache.commons.dbcp.ConnectionFactory} for that. The {@link org.apache.commons.dbcp.PoolableConnectionFactory} will take {@link java.sql.Connection}s created by the {@link org.apache.commons.dbcp.ConnectionFactory} and wrap them with classes that implement the pooling behaviour.
Several implementations of {@link org.apache.commons.dbcp.ConnectionFactory} are provided--one that uses {@link java.sql.DriverManager} to create connections ({@link org.apache.commons.dbcp.DriverManagerConnectionFactory}), one that uses a {@link java.sql.Driver} to create connections ({@link org.apache.commons.dbcp.DriverConnectionFactory}), one that uses a {@link javax.sql.DataSource} to create connections ({@link org.apache.commons.dbcp.DataSourceConnectionFactory}).
Q: I think I'm starting to get it, but can you walk me though it again?
A: Sure. Let's assume you want to create a {@link javax.sql.DataSource} that pools {@link java.sql.Connection}s. Let's also assume that that those pooled {@link java.sql.Connection}s should be obtained from the {@link java.sql.DriverManager}. You'll want to create a {@link org.apache.commons.dbcp.PoolingDataSource}.
The {@link org.apache.commons.dbcp.PoolingDataSource} uses an underlying {@link org.apache.commons.pool.ObjectPool} to create and store its {@link java.sql.Connection}.
To create a {@link org.apache.commons.pool.ObjectPool}, you'll need a {@link org.apache.commons.pool.PoolableObjectFactory} that creates the actual {@link java.sql.Connection}s. That's what {@link org.apache.commons.dbcp.PoolableConnectionFactory} is for.
To create the {@link org.apache.commons.dbcp.PoolableConnectionFactory}, you'll need at least two things:
In code, that might look like this:
GenericObjectPool connectionPool = new GenericObjectPool(null);
DriverManagerConnectionFactory connectionFactory = new DriverConnectionFactory("jdbc:some:connect:string",null);
PoolableConnectionFactory poolableConnectionFactory = new PoolableConnectionFactory(connectionFactory,connectionPool,null,null,false,true);
PoolingDataSource dataSource = new PoolingDataSource(connectionPool);
To create a {@link org.apache.commons.dbcp.PoolingDriver}, we do the same thing, except that instead of creating a {@link javax.sql.DataSource} on the last line, we create a {@link org.apache.commons.dbcp.PoolingDriver}, and register the connectionPool with it. E.g.,:
GenericObjectPool connectionPool = new GenericObjectPool(null);
DriverManagerConnectionFactory connectionFactory = new DriverConnectionFactory("jdbc:some:connect:string",null);
PoolableConnectionFactory poolableConnectionFactory = new PoolableConnectionFactory(connectionFactory,connectionPool,null,null,false,true);
PoolingDriver driver = new PoolingDriver();
driver.registerPool("example",connectionPool);
Since the {@link org.apache.commons.dbcp.PoolingDriver} registers itself with the {@link java.sql.DriverManager} when it is created, now you can just go to the {@link java.sql.DriverManager} to create your {@link java.sql.Connection}s, like you normally would:
Connection conn = DriverManager.getConnection("jdbc:apache:commons:dbcp:example");
Q: Sounds complicated, is there an easier way?
A: If you're using the {@link org.apache.commons.dbcp.PoolingDriver}, you don't need to do this configuration in code. Instead, you can provide a JOCL document that describes the connection pool, and let the {@link org.apache.commons.dbcp.PoolingDriver} discover it at runtime.
Specifically, if the {@link org.apache.commons.dbcp.PoolingDriver} is asked for a {@link java.sql.Connection} from a pool that has not yet been registered, it will look for a named resource from which to read the pool's configuration, and create that pool.
For example, suppose you create a pool named "/eg" from a JOCL document. The "connect string" for this pool will be "jdbc:apache:commons:dbcp:/eg". To do this, you'll need a create a resource (just a file in your classpath) containing a JOCL description of the pool. Specifically, this JOCL document should define a {@link org.apache.commons.dbcp.PoolableConnectionFactory} from which the pool will be obtained. For example:
<object class="org.apache.commons.dbcp.PoolableConnectionFactory" xmlns="http://apache.org/xml/xmlns/jakarta/commons/jocl">
<!-- the first argument is the ConnectionFactory -->
<object class="org.apache.commons.dbcp.DriverManagerConnectionFactory">
<string value="jdbc:some:connect:string"/>
<object class="java.util.Properties" null="true"/>
</object>
<!-- the next argument is the ObjectPool -->
<object class="org.apache.commons.pool.impl.GenericObjectPool">
<object class="org.apache.commons.pool.PoolableObjectFactory" null="true"/>
<int value="10"/> <!-- max active -->
<byte value="1"/> <!-- when exhausted action, 0 = fail, 1 = block, 2 = grow -->
<long value="2000"/> <!-- max wait -->
<int value="10"/> <!-- max idle -->
<boolean value="false"/> <!-- test on borrow -->
<boolean value="false"/> <!-- test on return -->
<long value="10000"/> <!-- time between eviction runs -->
<int value="5"/> <!-- number of connections to test per eviction run -->
<long value="5000"/> <!-- min evictable idle time -->
<boolean value="true"/> <!-- test while idle -->
</object>
<!-- the next argument is the KeyedObjectPoolFactory -->
<object class="org.apache.commons.pool.StackKeyedObjectPoolFactory">
<int value="5"/> <!-- max idle -->
</object>
<string value="SELECT COUNT(*) FROM DUAL"/> <;!-- validation query -->
<boolean value="false"/> <!-- default read only -->
<boolean value="true"/> <!-- default auto commit -->
</object>
Simply save that file somewhere in your classpath as eg.jocl, and the {@link org.apache.commons.dbcp.PoolingDriver} will find it automatically. You need only register the {@link org.apache.commons.dbcp.PoolingDriver} (for example, using the jdbc.drivers property), and use the the {@link java.sql.DriverManager} to create your {@link java.sql.Connection}s, like you normally would:
Connection conn = DriverManager.getConnection("jdbc:apache:commons:dbcp:/eg");
(Note that without the leading slash, the pool must be located at org/apache/commons/dbcp/PoolingDriver/eg.jocl within your classpath. See {@link java.lang.Class#getResource} for details.)