Knut Anders Hatlen wrote:
Derby doesn't provide connection pooling, but ConnectionPoolDataSource
can be used as a basic building block for a connection pool. A
ConnectionPoolDataSource creates PooledConnections, whereas a DataSource
creates Connections. A PooledConnection is just a wrapper around a
physical connection so that you can open/close logical Connection
objects without actually closing the underlying connection. Although
ConnectionPoolDataSource makes it easier to implement a connection pool,
it is possible to build a connection pool around DataSource too. I don't
know how the connection pool in Tomcat works, but if the example code
normally uses DataSource, I assume that it has implemented the wrapping
of the physical connections itself and you'll be fine with DataSource.
HTH,
It did, thanks.
In the end I didn't use the connection pool built into Tomcat. As far
as I can tell it requires that you set up a JNDI data source to
reference the pool. The problem with that is you have to put a copy of
the underlying JDBC driver into the global Tomcat /lib directory, as the
pool is set up before Tomcat starts up any webapps. This makes it
impossible to provide an entirely stand-alone WAR file that uses the
Tomcat connection pool.
Instead I used MiniConnectionPoolManager
(http://www.source-code.biz/snippets/java/8.htm) and passed it an
instance of the Derby ConnectionPoolDataSource class. I then layered a
custom implementation of DataSource on top of the pool manager, so I
could then set the custom DataSource as the default JSP data source, and
also push a reference to it into the webapp application scope. Here's
what I ended up with:
Custom DataSource->MiniConnectionPoolManager->ConnectionPoolDataSource
The only wrinkle was that MiniConnectionPoolManager doesn't cache
connections by user ID, so I had to make the
getConnection(String username, String password)
method in the custom DataSource throw an exception if it was called.
This was no big deal as my application only uses a single username to
access the database.
--
Alan Burlison
--
