Problem using URLClassLoader

[Gabrielle Littler]

Hi,

I'm trying to dynamically add a jar to the classpath at runtime by using a URLClassLoader. The first time I try to load a class my class loader I get a ClassNotFoundException.

Here's my code:

package com.bbt.planner.util;

import java.io.File;
import java.net.URI;
import java.net.URL;
import java.net.URLClassLoader;

public class PlClientGo
{
	public static void main(String[] args)
	{
		try
		{

// Logging	
ClassLoader parent = PlClientGo.class.getClassLoader();
			logUrls(parent, "original loader");

			File file = new File("C:\\dev\\bbt\\test\\planner\\version\\planner.jar");
			URI uri = file.toURI();
			URL url = uri.toURL();
			System.out.println("Raw file: " + url);

			URLClassLoader cl = new URLClassLoader(new URL[] { url }, PlClientGo.class.getClassLoader());
			logUrls(cl, "custom loader");

			ClassLoader parent2 = cl.getParent();
			logUrls(parent2, "parent loader");

// The interesting bit
			Class<?> clazz = cl.loadClass("com.bbt.planner.util.MyClass");
			Object main = clazz.newInstance();
			ClassLoader test = main.getClass().getClassLoader();
			((MyClass) main).go();
		}
		catch (Exception e)
		{
			e.printStackTrace(System.out);
		}	
	}

	private static void logUrls(ClassLoader cl, String desc)
	{
		if (cl instanceof URLClassLoader)
		{
			URLClassLoader urlCl = (URLClassLoader) cl;
			URL[] urls = urlCl.getURLs();
			int i = 0;
			for (URL u : urls)
			{
				i++;
				System.out.println(i + " URL in " + desc + ": " + u);
			}
		}
		else
		{
			System.out.println("Not a URL classloader");
		}
	}
}

package com.bbt.planner.util;

public class MyClass
{
	public void go()
	{
		System.out.println("Go");
	}
}

I added some logging to find out what URLs were referenced by the class loader and it's parent class loader, and tried running a few different test cases. If I run my app as intended, I get the following:

java -cp launcher.jar com.bbt.planner.util.PlClientGo
1 URL in custom loader: file:/C:/dev/bbt/test/planner/version/planner.jar
1 URL in parent loader: file:/C:/dev/bbt/test/planner/launcher.jar

Exception in thread "main" java.lang.NoClassDefFoundError: com/bbt/planner/util/
MyClass
at com.bbt.planner.util.PlClientGo.main(PlClientGo.java:45)
Caused by: java.lang.ClassNotFoundException: com.bbt.planner.util.MyClass
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClassInternal(Unknown Source)
... 1 more

If, however, I run explicitly pathing in my jar in the class path the code works and I get:

java -cp launcher.jar;version/planner.jar com.bbt.planner.util.PlClientGo -verbose
1 URL in custom loader: file:/C:/dev/bbt/test/planner/version/planner.jar
1 URL in parent loader: file:/C:/dev/bbt/test/planner/launcher.jar
2 URL in parent loader: file:/C:/dev/bbt/test/planner/version/planner.jar

What's interesting about that is that the URL held in the class loader I instantiated myself is exactly the same as the one in the parent class loader that was generated by the '-cp' when I ran the second test case. I.e. my jar is in the correct place with the correct class in it, but for some reason my URLClassLoader isn't able to load the class if it isn't found by parent delegation.

Any ideas about what could be wrong or where to look / what to try next would be greatly appreciated.