An object that provides hooks for connection pool management. A
PooledConnection
object represents a physical connection to a data source. The connection can be recycled rather than being closed when an application is finished with it, thus reducing the number of connections that need to be made.
An application programmer does not use the PooledConnection
interface directly; rather, it is used by a middle tier infrastructure that manages the pooling of connections.
When an application calls the method DataSource.getConnection
, it gets back a Connection
object. If connection pooling is being done, that Connection
object is actually a handle to a PooledConnection
object, which is a physical connection.
The connection pool manager, typically the application server, maintains a pool of PooledConnection
objects. If there is a PooledConnection
object available in the pool, the connection pool manager returns a Connection
object that is a handle to that physical connection. If no PooledConnection
object is available, the connection pool manager calls the ConnectionPoolDataSource
method getPoolConnection
to create a new physical connection. The JDBC driver implementing ConnectionPoolDataSource
creates a new PooledConnection
object and returns a handle to it.
When an application closes a connection, it calls the Connection
method close
. When connection pooling is being done, the connection pool manager is notified because it has registered itself as a ConnectionEventListener
object using the ConnectionPool
method addConnectionEventListener
. The connection pool manager deactivates the handle to the PooledConnection
object and returns the PooledConnection
object to the pool of connections so that it can be used again. Thus, when an application closes its connection, the underlying physical connection is recycled rather than being closed.
If the connection pool manager wraps or provides a proxy to the logical handle returned from a call to PoolConnection.getConnection
, the pool manager must do one of the following when the connection pool manager closes or returns the PooledConnection
to the pool in response to the application calling Connection.close
:
- call
endRequest
on the logical Connection
handle
- call
close
on the logical Connection
handle
The physical connection is not closed until the connection pool manager calls the PooledConnection
method close
. This method is generally called to have an orderly shutdown of the server or if a fatal error has made the connection unusable.
A connection pool manager is often also a statement pool manager, maintaining a pool of PreparedStatement
objects. When an application closes a prepared statement, it calls the PreparedStatement
method close
. When Statement
pooling is being done, the pool manager is notified because it has registered itself as a StatementEventListener
object using the ConnectionPool
method addStatementEventListener
. Thus, when an application closes its PreparedStatement
, the underlying prepared statement is recycled rather than being closed.