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From "John Trimble (JIRA)" <j...@apache.org>
Subject [jira] Updated: (JXPATH-127) Change dynamic class loading to consult context class loader.
Date Wed, 25 Feb 2009 07:05:01 GMT

     [ https://issues.apache.org/jira/browse/JXPATH-127?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

John Trimble updated JXPATH-127:
--------------------------------

    Attachment: jxpath-14-classloading-lang-port.patch

A port of [lang]'s class loading code with some modifications to avoid pulling in unnecessary
classes from [lang].

> Change dynamic class loading to consult context class loader.
> -------------------------------------------------------------
>
>                 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
>
>         Attachments: classloading_fix_jxpath14.patch, jxpath-14-classloading-lang-port.patch,
jxpath-14-classloading-widest-scope.patch
>
>
> 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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