JDK1.7 ClassLoader Memory Leak

Question

I have child-first UrlClassLoader to load jar file dynamically. Then I do a reflection to invoke a method within loaded jar file. Once it is finished, I prefer to unload the classloader. Then I try to do some stress test code to make sure my code run smoothly. Basically, what I try to do is load and unload jar within looping statement. Here is my code:

    for (int i = 0; i < 1000; i++) {
        //Just to show the progress
        System.out.println("LOAD NUMBER : " + i);

        ChildFirstURLClassLoader classLoader = null;
        try {
            File file = new File("C:\\library.jar");
            String classToLoad = "com.test.MyClass";
            URL jarUrl = new URL("file:" + file.getAbsolutePath());

            classLoader = new ChildFirstURLClassLoader(new URL[] {jarUrl}, null);
            Class<?> loadedClass = classLoader.loadClass(classToLoad);
            Method method = loadedClass.getDeclaredMethod("execute",
                    new Class[] {});

            ClassLoader currCl= Thread.currentThread().getContextClassLoader();
            Thread.currentThread().setContextClassLoader(classLoader);
            method.invoke(null);
            Thread.currentThread().setContextClassLoader(currCl);

            method = null;
            loadedClass = null;
        } finally {
            if (classLoader != null) {
                classLoader.close();
                classLoader = null;
            }
        }
    }

When I'm running this code under JDK1.6, without classLoader.close(); statement, that code runs perfectly. But when I turn into JDK1.7, sometimes I get java.lang.OutOfMemoryError: PermGen space error. Unfortunately it occurs in inconsistent manner.

Answer 1

The easiest way to confirm where the leak comes from is to use a profiler to monitor the memory usage. Try JProfiler, or VisualVM. It will enable you to pinpoint the exact location of the leak, and also give you clues as to whether and how you can fix it.