Change dynamic class loading to consult context class loader.
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Key: JXPATH-127
URL: https://issues.apache.org/jira/browse/JXPATH-127
Project: Commons JXPath
Issue Type: Improvement
Reporter: John Trimble
Fix For: post-1.3
For dynamically loading classes, JXPath currently uses Class.forName(...). This
means all classes loaded by JXPath must be visible to whatever class loader
loaded JXPath. This is restrictive in large frameworks and web applications
where multiple class loaders are in use. In particular, in an EJB3 application
deployed on Weblogic, the shared jars between different EJB modules are loaded
with a separate class loader than the modules themselves. Consequently, if the
jxpath.jar is among the general libraries for the application, then a specific
EJB module will be unable to reference static methods of classes within its own
module in an xpath expression. For example, consider the following lines of
code in an EJB module class:
JXPathContext context = JXPathContext.newContext(new Object());
Object value = context.getValue("SomeClass.getSomething()");
This will fail, with a ClassNotFoundException, if SomeClass is a class in the
module, but jxpath is a general library for the application.
Attached (or will be once I figure out how) is a patch for JXPath that gets
around this issue. The patch changes the class loading strategy to use the
context class loader, when it appears appropriate, to dynamically load classes.
The strategy is based on suggestions and example code from:
http://www.javaworld.com/javaworld/javaqa/2003-06/01-qa-0606-load.html
Assuming all class loaders involved delegate to their parent class loader (as
recommended in the API), currently working code, that uses JXPath, should only
be affected by this change if the current class loader (the class loader that
loaded JXPath) is not in an ancestor/descendant relationship with the context
class loader.
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