Bill,

This is fabulous stuff. Good job.

Is there a way we might be able to use the AOP xml to dynamically do
your example below (as well as the clustered and remoting) for POJOs
during construction time?  In other words, could you not have an
interceptor on a constructor pointcut that would do this for you and
dynamically make the class Versionable, Clusterable, Remotable, etc. so
that the actual instance you receive back has these capabilities
transparently w/o having to programatically do this?

The advantages of this would be that you could dynamically modify the
POJO from the XML file without having to do it programmatically (of
course, you could if you wanted to).  That way, we can truly separate
the business logic (as an example, no flames here) from the
cross-cutting of concerns such as transactibility, security, remoteness,
etc.   

Looking at the jboss-aop.xml in the testsuite - it looks like you're
doing this with the Tx Interceptor on the VersionedPOJO - why not just
create the VersionedPOJO in the same way and insert the Versioned
Interceptor the same way? Is this possible? 

Jeff 

-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Bill
Burke
Sent: Wednesday, March 26, 2003 7:09 PM
To: Jboss-Dev
Subject: [JBoss-dev] AOP versioned ACID objects 1st iteration


I have implemented a new AOP service for Serializable POJOs, Versioned
Objects.  You can transactionally version an object.  If you modify the
object within a transaction, this modification is not seen by other
transactions.  If the tx commits, the changes seen, if a rollback
happens the changes are rolled back.  On commit, if another tx has
modified the object, the tx will rollback (OptimisticLocking).

The way it works is as follows:

POJO pojo = new POJO();
pojo = (POJO)org.jboss.aop.plugins.Versioned.makeVersioned(pojo);

calling Versioned.makeVersioned creates a proxy that sits in front of
the real object.

transactionManager.begin();

pojo.callMethod();

when callMethod is invoked since there is a transaction, an interceptor
creates a copy of the REAL pojo and does all further invocations on this
copy.

pojo.someField = 5;

If you have field interception turned on, public field will also be
accessed via the copy/version

tm.commit();

On commit, a tx Synchronization checks to see if the version you have
created is the latest and greatest.  If not an
org.jboss.aop.plugins.OptimisticLockFailure exception is thrown in
beforeCompletion.  I'm not sure how this exception is wrapped.

Some other semantics:

1. All method invocations force a version to be created.  You can avoid
this by declared class-metadata as follows:

<class-metadata name="234234" group="VERSIONED"
class="org.jboss.test.aop.bean.VersionedPOJO">
<method name="get.*">
  <read-only>true</read-only>
</method>
</class-metadata>

A readonly method will not cause the creation of a version and the
current object will be used.


An example and unit test is under
testsuite/src/main/org/jboss/test/aop/bean/VersionedObjectTester.java

The example object VersionedPOJO.java, has 1 interceptor pointcut
declared on the class to do Tx stuff.  See
testsuite/src/resources/aop/META-INF/jboss-aop.xml for more details.

What would be nice is to also write a TransactionalLock interceptor for
versioned POJO's that have high OptimisticLock failures.

Bill




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