ParentLastClassLoader

ParentLastClassLoader.java

import java.net.URL;
import java.net.URLClassLoader;

public class ParentLastClassLoader extends ClassLoader {

	private ChildURLClassLoader childClassLoader;

	/**
	 * This class allows me to call findClass on a classloader
	 */
	private static class FindClassClassLoader extends ClassLoader {
		public FindClassClassLoader(ClassLoader parent) {
			super(parent);
		}

		@Override
		public Class<?> findClass(String name) throws ClassNotFoundException {
			return super.findClass(name);
		}
	}

	/**
	 * This class delegates (child then parent) for the findClass method for a
	 * URLClassLoader. We need this because findClass is protected in
	 * URLClassLoader
	 */
	private static class ChildURLClassLoader extends URLClassLoader {
		private FindClassClassLoader realParent;

		public ChildURLClassLoader(URL[] urls, FindClassClassLoader realParent) {
			super(urls, null);

			this.realParent = realParent;
		}

		@Override
		public Class<?> findClass(String name) throws ClassNotFoundException {
			try {
				// first try to use the URLClassLoader findClass
				return super.findClass(name);
			} catch (ClassNotFoundException e) {
				// if that fails, we ask our real parent classloader to load the
				// class (we give up)
				return realParent.loadClass(name);
			}
		}
	}

	public ParentLastClassLoader(ClassLoader parent, URL[] urls) {
		super(parent);
		// super(Thread.currentThread().getContextClassLoader());

		childClassLoader = new ChildURLClassLoader(urls,
				new FindClassClassLoader(this.getParent()));
	}

	@Override
	protected synchronized Class<?> loadClass(String name, boolean resolve)
			throws ClassNotFoundException {
		try {
			// first we try to find a class inside the child classloader
			return childClassLoader.findClass(name);
		} catch (ClassNotFoundException e) {
			// didn't find it, try the parent
			return super.loadClass(name, resolve);
		}
	}

}