ClassNotFoundException using Digester

[tsangcn]

Hello

I am running JBoss 3.0.4 with JDK 1.4.1

My app is a webapp contains in a single WAR file
I have a SetupServlet which will be run when my web app starts

It will read a list of datasource descriptors from an XML using Apache Digester package


I have add a rule as follows

digester.addObjectCreate("datasources", "misc.DataSourceDescriptors");

But when the digester parse the XML, I get the following exception (taken from server.log)

2002-11-20 21:00:29,203 ERROR [org.apache.commons.digester.Digester] Begin event threw exception
java.lang.ClassNotFoundException: misc.DataSourceDescriptors
at java.net.URLClassLoader$1.run(URLClassLoader.java:198)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:186)
at org.jboss.mx.loading.UnifiedClassLoader.findClass(UnifiedClassLoader.java:239)
at java.lang.ClassLoader.loadClass(ClassLoader.java:299)
at org.jboss.mx.loading.UnifiedClassLoader.loadClassLocally(UnifiedClassLoader.java:247)
at org.jboss.mx.loading.ClassLoadingTask$ThreadTask.run(ClassLoadingTask.java:84)
at org.jboss.mx.loading.LoadMgr.nextTask(LoadMgr.java:234)
at org.jboss.mx.loading.UnifiedClassLoader3.loadClass(UnifiedClassLoader3.java:144)
at java.lang.ClassLoader.loadClass(ClassLoader.java:255)
at org.apache.commons.digester.ObjectCreateRule.begin(ObjectCreateRule.java:252)
at org.apache.commons.digester.Digester.startElement(Digester.java:1237)
at org.apache.crimson.parser.Parser2.maybeElement(Parser2.java:1490)
at org.apache.crimson.parser.Parser2.parseInternal(Parser2.java:500)
at org.apache.crimson.parser.Parser2.parse(Parser2.java:305)
at org.apache.crimson.parser.XMLReaderImpl.parse(XMLReaderImpl.java:442)
at org.apache.commons.digester.Digester.parse(Digester.java:1514)
at misc.SetupServlet.init(SetupServlet.java:69)
at javax.servlet.GenericServlet.init(GenericServlet.java:256)
at org.mortbay.jetty.servlet.ServletHolder.start(ServletHolder.java:225)
at org.mortbay.jetty.servlet.ServletHandler.initializeServlets(ServletHandler.java:444)
at org.mortbay.jetty.servlet.WebApplicationHandler.initializeServlets(WebApplicationHandler.java:163)
at org.mortbay.jetty.servlet.WebApplicationContext.start(WebApplicationContext.java:492)
at org.mortbay.j2ee.J2EEWebApplicationContext.start(J2EEWebApplicationContext.java:85)
at org.jboss.jetty.Jetty.deploy(Jetty.java:414)
at org.jboss.jetty.JettyService.performDeploy(JettyService.java:243)
at org.jboss.web.AbstractWebContainer.start(AbstractWebContainer.java:300)
at org.jboss.deployment.MainDeployer.start(MainDeployer.java:807)
at org.jboss.deployment.MainDeployer.deploy(MainDeployer.java:621)
at org.jboss.deployment.MainDeployer.deploy(MainDeployer.java:585)
at sun.reflect.GeneratedMethodAccessor10.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:324)
at org.jboss.mx.capability.ReflectedMBeanDispatcher.invoke(ReflectedMBeanDispatcher.java:284)
at org.jboss.mx.server.MBeanServerImpl.invoke(MBeanServerImpl.java:517)
at org.jboss.util.jmx.MBeanProxy.invoke(MBeanProxy.java:174)
at $Proxy4.deploy(Unknown Source)
at org.jboss.deployment.scanner.URLDeploymentScanner.deploy(URLDeploymentScanner.java:435)
at org.jboss.deployment.scanner.URLDeploymentScanner.scan(URLDeploymentScanner.java:561)
at org.jboss.deployment.scanner.AbstractDeploymentScanner$ScannerThread.doScan(AbstractDeploymentScanner.java:212)
at org.jboss.deployment.scanner.AbstractDeploymentScanner$ScannerThread.loop(AbstractDeploymentScanner.java:225)
at org.jboss.deployment.scanner.AbstractDeploymentScanner$ScannerThread.run(AbstractDeploymentScanner.java:202)

I have checked many times that the class misc.DataSourceDescriptors is there
and there are no spelling mistakes

It seems is that the JBoss UCL cannot find the class, why?

My WAR file is deployed in server/default/deploy
the jar files for the Digester package is in server/default/lib
the class which is not found by UCL is there WEB-INF/classes/misc/DataSourceDescriptors.class in my WAR file


Please help

Thanks
CN

[jules]

welcome to the wonderful world of ClassLoaders....

Look up your stack...

Notice Digester calling UCL calling loadClass ?

Because you have Digester in server/default/lib it is being loaded into a ClassLoader higher up the hierarchy than the one into which your webapp is loaded.

When it needs to load classes it SHOULD use Thread.current().getContextClassLoader() to get the correct ClassLoader (put into a threadlocal).

I'll bet you a virtual beer it is simply and naively calling Class.forName(), which will use the ClassLoader into which it was loaded.

Put digester in WEB-INF/lib.
Pray that the people who wrote crimson (which is probably also in server/default/lib) got it right.
Try again.

If that works, post a bug on the digester list and give them a heads up.


Jules

[jules]

so - did it work ?

Jules

[lmagee]

Another approach: try adding

digester.setUseContextClassLoader(true);

This fixed another problem with Digester.

[tsangcn]

Hello

Sorry for my late reply.

After using digester.setUseContextClassLoader(true)
everything is OK

Thanks
CN