| An interface which provides facilities for handling connections to a database
which are pooled.
Typically, a PooledConnection is recycled when it is no longer required by an
application, rather than being closed and discarded. The reason for treating
connections in this way is that it can be an expensive process both to
establish a connection to a database and to destroy the connection. Reusing
connections through a pool is a way of improving system performance and
reducing overhead.
It is not intended that an application use the PooledConnection interface
directly. The PooledConnection interface is intended for use by a component
called a Connection Pool Manager, typically part of the infrastructure that
supports use of the database by applications.
Applications obtain connections to the database by calling the
DataSource.getConnection method. Under the covers, the
Connection Pool Manager will get a PooledConnection object from its
connection pool and passes back a Connection object that wraps or references
the PooledConnection object. A new PooledConnection object will only be
created if the pool is empty.
When the application is finished using a PooledConnection, the application
calls the Connection.close method. The Connection Pool Manager
is notified via a ConnectionEvent from the Connection that this has happened
(the Pool Manager registers itself with the Connection before the Connection
is given to the application). The Pool Manager removes the underlying
PooledConnection object from the Connection and returns it to the pool for
reuse - the PooledConnection is thus recycled rather than being destroyed.
The connection to the database represented by the PooledConnection is kept
open until the PooledConnection object itself is deactivated by the
Connection Pool Manager, which calls the PooledConnection.close
method. This is typically done if there are too many inactive connections in
the pool, if the PooledConnection encounters a problem that makes it unusable
or if the whole system is being shut down.
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