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From "Niall Pemberton" <niall.pember...@gmail.com>
Subject Fwd: [DBCP] Managed Connection support
Date Wed, 04 Jul 2007 01:45:28 GMT
Forwarding to Commons Dev...

---------- Forwarded message ----------
From: Dain Sundstrom <dain@iq80.com>
Date: Jul 4, 2007 2:21 AM
Subject: [DBCP] Managed Connection support
To: Jakarta General List <general@jakarta.apache.org>


I just posted a patch JIRA which adds support for container managed
connections to DBCP.  In an environment where you have an accessible
transaction manger such as Tomcat (when installed), Geronimo or
OpenEJB, this patch allows adds support for pooling managed
connections to an XA or non-XA data base.

There are many libraries that use DBCP for non-managed environments,
but when additional resources such as a JMS provider are added to the
mix, they have to replace DBCP with something else.  If you search
google for XA and DBCP, you will loads of painful direction on how to
replace DBCP with something else.  I personally want to use DBCP in
Tomcat with ActiveMQ.

Anyways, enough with motivation....

To use the new code, you need access to a TranactionManager (this
code just creates a new Geronimo one).

         transactionManager = new TransactionManagerImpl();

Then you either create an XADataSource and
DataSourceXAConectionFactory or as this code does, create a normal
DBCP ConnectionFactory and wrap it with a LocalXAConectionFactory

         Properties properties = new Properties();
         properties.setProperty("user", "username");
         properties.setProperty("password", "password");
         ConnectionFactory connectionFactory = new
DriverConnectionFactory(
                 new TesterDriver(),
                 "jdbc:apache:commons:testdriver", properties);

         // wrap it with a LocalXAConnectionFactory
         XAConnectionFactory xaConnectionFactory = new
LocalXAConnectionFactory(
                 transactionManager,
                 connectionFactory);


Now you create a pool as normal (full reuse here).

         pool = new GenericObjectPool();
         pool.setMaxActive(getMaxActive());
         pool.setMaxWait(getMaxWait());

         // create the pool object factory
         PoolableConnectionFactory factory = new
PoolableConnectionFactory(
                 xaConnectionFactory,
                 pool,
                 null,
                 "SELECT DUMMY FROM DUAL",
                 true,
                 true);
         pool.setFactory(factory);


Finally, you create a special ManagedDataSource using the pool above
and the special TransactionRegistry object obtained from the
XAConnectionFactory.

         ds = new ManagedDataSource(pool,
xaConnectionFactory.getTransactionRegistry());
         ds.setAccessToUnderlyingConnectionAllowed(true);


That's it.  The data source and connections work as normal until you
start a transaction using the TransactionManager.  When you use a
connection while the transaction is active, the connection is
enlisted in the transaction.  When the transaction is complete, the
connection is committed (or rolledback) and the connection returns to
normal.

Most of the new code extends existing classes or uses existing
classes without modification.  The key to this reuse is the
TransactionRegistry abstraction which maintains a map from the
Connection to the XAResource for that connection.  The XAResource is
needed to enlist a connection in a transaction.  The
TransactionRegistry and associated TransationContext class
encapsulate all interactions with the TransactionManager leaving the
Connection implementation relatively simple (making reuse easier).

For now the code is contained in the org.apache.commons.dbcp.managed
package, but I would suspect we may want to spread it out amongst the
existing packages instead of creating a feature specific package.
I'm also not sure what additional interfaces people may want such as
equivalents of the BasicDataSource or BasicDataSourceFactory.

The code has tests and has javadoc, but it needs real world testing
and some real docs.  I'm going try hooking it into OpenEJB and
running it's massive test suite with a couple of opensource DBs.

Anyways, I hope you all like it and accept the patch.  I'm around to
help with changes or whatever.  I also ran into a few bugs while
working on this that are already reported in JIRA (like the close
bugs) and am willing to help with those also.

-dain



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