WebSphere and Class Reloading

[casterx <ca...@netzero.net>]

After version 0.97 (I believe) of OJB, WebSphere started to require full
server resert in order to get OJB to catch up on the reloaded classes. I
sent a note to IBM tech support and here's what they came up with. I hope
this information is usable to you guys.


Following is the update from our L3 team:

Action taken: Has been gathering logs/traces to investigate the
problem. So far, have narrowed the problem arises at place where
there's a programmatically class loading using forname in
ConfigurationAbstractImpl.java which behave differently after class
change and web module reloading.
Action plan: Will check to see if that's caused by the WAS classloader
and work on a patch to fix the problem if necessary.


After looking this problem for awhile, I have found out 2
Class.forName() call are causing the problem in the Apache OJB library
"db-ojb-1.0.rc1.jar".  I've got the application working after making
 2 changes:
(1) ConfigurationAbstractImpl.java in
org/apache/ojb/broker/util/configuration/impl
change the forName call to like:
clazz =
Thread.currentThread().getContextClassLoader().loadClass(className);
(2) ClassHelper.java in org/apache/ojb/broker/util
change the forName call to like:
return
Thread.currentThread().getContextClassLoader().loadClass(className);
However, since that function in ClassHelper.java is also used to load
the Oracle JDBC driver too, you will need to make a special case to let
it still use forName() when loading the JDBC driver.  By the way, this
 approach of loading JDBC driver yourself is not recommended on
WebSphere.  First, you are on your own to handling all the low level
JDBC connection details and skipping the nice pooling and datasource
DB connection features available and managed by WebSphere.  Also, this
approach could pose a scalability issue.




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