Requiring and using a Java library that ends up using a Thread Context
classloader doesn't work.
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Key: JRUBY-2495
URL: http://jira.codehaus.org/browse/JRUBY-2495
Project: JRuby
Issue Type: Bug
Components: Java Integration
Affects Versions: JRuby 1.1.2
Environment: MacOS 1.5.2, Java 1.5.0_13, JRuby trunk r6630
Reporter: Stephen Bannasch
Priority: Critical
Requiring and using a Java library that ends up using a Thread Context
classloader doesn't work.
I'm integrating some Java code into my JRuby project and adding the jars to
JRuby's classpath using require.
The external Java code uses other libraries that use a Thread Context
classloader. When the ThreadContext classloader tries to create a class that is
defined in one of the jars I required from JRuby I get a ClassNotFoundException.
If I add the jars to the system CLASSPATH everything works.
This problem came up while trying to integrate our SAIL-OTrunk code however
we've created a much simpler test to show the problem.
Trac:
http://trac.cosmos.concord.org/projects/browser/trunk/common/misc/context-classloader-test
Setting up the test:
{code}
svn co
https://svn.concord.org/svn/projects/trunk/common/misc/context-classloader-test
cd context-classloader-test
mkdir -p lib/test/contextclassloader
javac -sourcepath src/ -d lib/ src/test/contextclassloader/Main.java
cp src/test/contextclassloader/configuration.xml lib/test/contextclassloader/
jar cf context-classloader.jar -C lib test/contextclassloader/
{code}
Running the tests:
failing test:
{code}
$ jruby main.rb
java.lang.ClassNotFoundException: test.contextclassloader.ConfigurableClass
Continuing ...
java.lang.NullPointerException: target should not be null
Continuing ...
java.lang.NullPointerException: target should not be null
Continuing ...
java.lang.NullPointerException: target should not be null
Continuing ...
nil
{code}
passing test:
{code}
$ export CLASSPATH=$CLASSPATH:`pwd`/context-classloader.jar
$ jruby main.rb
[EMAIL PROTECTED] name: really cool name goes here
{code}
Here's some of the investigation I did when I was originally looking into the
classloading issues running OTrunk from JRuby.
The problem occurs when a Java class I call then calls XMLDecoder to
instantiate another Java class -- XMLDecoder is not using the JRuby classloader
-- instead it is using a thread context classloader and can't find the class
it's trying to create because only the JRuby classloader has the new jars I've
required
In JRuby the thread context classloader is the parent of the jruby classloader.
See my experiments here:
http://pastie.org/177613
When I contacted Charles Nutter on IRC he wrote that JRuby is not setting the
threadcontext classloader when the JRuby thread is created to make it easier to
create new JRuby thread instances.
bq. the problem we would have setting the jruby loader as thread context
classloader is...what happens if the thread calls through to another JRuby
instance? since the jaxp libs are loaded by system classloader, in order for
them to locate and instantiate classes from lower classloaders it looks at tc
classloader -- we don't set tc classloader to the jruby classloader because,
well, we really can't if we want jruby instances to be able to migrate across
threads
I don't know enough about the JRuby threading to know why using a ThreadContext
classloader would hinder or prevent migrating JRuby instances across threads.
You can see more of the IRC conversation between me and Charles starting around
01:05:43 here:
* http://kessel.ilrt.bris.ac.uk/jruby/logs/2008-04-09.html
Recent threads mentioning related issues:
Chris Evans-8:
"When I add the websphere jars to the classpath in the jruby executable, it
works.
If I append the jars in the script, either through $CLASSPATH << or 'require
blah.jar', the script fails."
http://www.nabble.com/Dynamically-adding-to-classpath-td15841856.html
Lenny Marks:
"..trying to use the Spring's ClassPathXmlApplicationContext, but it seems
that
internally, Springkeeps trying to load stuff with the Thread's
contextClassLoader"
http://www.ruby-forum.com/topic/127354#568081
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