Description Michael Schierl 2013-02-16 16:25:58 EST

This bug mostly happens for me when debugging two JSP webapps that run on the same Tomcat server and share a common project dependency.

To make it easier to reproduce without all that setup, here is a contrived minimal example to reproduce the bug without needing any WST plugins or Tomcat:

* In your workspace, create two Java projects, "Loader" and "Loaded". Do not add any build path dependencies between them.

* Add this class to the Loaded project:

//////////////////////////////////////////////////////////////////////
import java.util.*;

public class LoadedThread extends Thread {
	
	private static List<String> staticList = new ArrayList<String>();
	private String value;
	
	public LoadedThread(String value) {
		this.value = value;
		start();
	}
	
	@Override
	public void run() {
		staticList.add(value);
		// place breakpoint in next line:
		System.out.println(staticList);
	}
}
//////////////////////////////////////////////////////////////////////

* Add this class to the Loader project (in case the name of the Loaded project is different or your output folder is not called "bin", don't forget to update the path in the first line of the main method):

//////////////////////////////////////////////////////////////////////
import java.io.*;
import java.net.*;

public class CustomLoader {
	public static void main(String[] args) throws Exception {
		URL[] urls = new URL[] {new File("../Loaded/bin").toURI().toURL()};
		URLClassLoader loader1 = new URLClassLoader(urls);
		URLClassLoader loader2 = new URLClassLoader(urls);
		loader1.loadClass("LoadedThread").getConstructor(String.class).newInstance("First");
		loader2.loadClass("LoadedThread").getConstructor(String.class).newInstance("Second");
	}
}
//////////////////////////////////////////////////////////////////////

* Run this class as "Java Application", it should output both "[First]" and "[Second]" (in unpredictable order).

* Edit the run configuration of the Java Application: on the source tab, add "Loaded" project to source lookup path (or debugger will not find it in next step).

* Place breakpoint as described in the comment of the "Loaded" class and run again in debug mode. Two breakpoints should fire in two different threads.

* Select the threads in the Debug view and hover over the "value" and "staticList" variables with the mouse until a small window appears that shows the current values. 

Actual result: 
You will observe, that in one of the two threads, the "staticList" variable shows the variable of the wrong class loader (in my example, the second thread had value "Second" but staticList "[First]").

Expected result:
One thread should have value "First" and staticList "[First]", the other should have value "Second" and staticList "[Second]".

Thanks for reading, and of course for fixing :-)