JoinClassLoader.java

package NetworkAdapter.Implementation;

import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.nio.ByteBuffer;
import java.util.Enumeration;
import java.util.Vector;

/**
 * A class loader that combines multiple class loaders into one.<br>
 * The classes loaded by this class loader are associated with this class loader,
 * i.e. Class.getClassLoader() points to this class loader.
 * <p>
 * Author Christian d'Heureuse, Inventec Informatik AG, Zurich, Switzerland, www.source-code.biz<br>
 * License: LGPL, http://www.gnu.org/licenses/lgpl.html<br>
 * Please contact the author if you need another license.
 */
public class JoinClassLoader extends ClassLoader {

    private ClassLoader[] delegateClassLoaders;

    public JoinClassLoader (ClassLoader parent, ClassLoader... delegateClassLoaders) {
        super (parent);
        this.delegateClassLoaders = delegateClassLoaders; }

    protected Class<?> findClass (String name) throws ClassNotFoundException {
        // It would be easier to call the loadClass() methods of the delegateClassLoaders
        // here, but we have to load the class from the byte code ourselves, because we
        // need it to be associated with our class loader.
        String path = name.replace('.', '/') + ".class";
        URL url = findResource(path);
        if (url == null) {
            throw new ClassNotFoundException (name); }
        ByteBuffer byteCode;
        try {
            byteCode = loadResource(url); }
        catch (IOException e) {
            throw new ClassNotFoundException (name, e); }
        return defineClass(name, byteCode, null); }

    private ByteBuffer loadResource (URL url) throws IOException {
        InputStream stream = null;
        try {
            stream = url.openStream();
            int initialBufferCapacity = Math.min(0x40000, stream.available() + 1);
            if (initialBufferCapacity <= 2)
                initialBufferCapacity = 0x10000;
            else
                initialBufferCapacity = Math.max(initialBufferCapacity, 0x200);
            ByteBuffer buf = ByteBuffer.allocate(initialBufferCapacity);
            while (true) {
                if (!buf.hasRemaining()) {
                    ByteBuffer newBuf = ByteBuffer.allocate(2*buf.capacity());
                    buf.flip();
                    newBuf.put (buf);
                    buf = newBuf; }
                int len = stream.read(buf.array(), buf.position(), buf.remaining());
                if (len <= 0) break;
                buf.position (buf.position()+len); }
            buf.flip();
            return buf; }
        finally {
            if (stream != null) stream.close(); }}

    protected URL findResource (String name) {
        for (ClassLoader delegate : delegateClassLoaders) {
            URL resource = delegate.getResource(name);
            if (resource != null) return resource; }
        return null; }

    protected Enumeration<URL> findResources (String name) throws IOException {
        Vector<URL> vector = new Vector<URL>();
        for (ClassLoader delegate : delegateClassLoaders) {
            Enumeration<URL> enumeration = delegate.getResources(name);
            while (enumeration.hasMoreElements()) {
                vector.add (enumeration.nextElement()); }}
        return vector.elements(); }

} // end class JoinClassLoader