JarClassLoader.java

package org.apache.s4.base.util;

import java.io.Closeable;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URL;
import java.net.URLClassLoader;
import java.security.CodeSource;
import java.security.ProtectionDomain;
import java.util.Enumeration;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;

/**
 * Our goal is to be able to put apps and dependent classes in a single jar that
 * we can easily read using a URL.
 * 
 * With derived work from <a href=
 * "http://qdolan.blogspot.com/2008/10/embedded-jar-classloader-in-under-100.html"
 * >this blog</a>.
 * 
 * @author Leo Neumeyer
 * 
 */
public class JarClassLoader extends URLClassLoader {

    private static void close(Closeable closeable) {
        if (closeable != null) {
         try {
          closeable.close();
         } catch (IOException e) {
          e.printStackTrace();
         }
        }
       }
       
       private static boolean isJar(String fileName) {
        return fileName != null && fileName.toLowerCase().endsWith(".jar");
       }
       
       private static File jarEntryAsFile(JarFile jarFile, JarEntry jarEntry) throws IOException {
        InputStream input = null;
        OutputStream output = null;
        try {
         String name = jarEntry.getName().replace('/', '_');
         int i = name.lastIndexOf(".");
         String extension = i > -1 ? name.substring(i) : "";
         File file = File.createTempFile(name.substring(0, name.length() - extension.length()) + ".", extension);
         file.deleteOnExit();
         input = jarFile.getInputStream(jarEntry);
         output = new FileOutputStream(file);
         int readCount;
         byte[] buffer = new byte[4096];
         while ((readCount = input.read(buffer)) != -1) {
          output.write(buffer, 0, readCount);
         }
         return file;
        } finally {
         close(input);
         close(output);
        }
       }

       public JarClassLoader(URL[] urls, ClassLoader parent) {
        super(urls, parent);
        try {
         ProtectionDomain protectionDomain = getClass().getProtectionDomain();
         CodeSource codeSource = protectionDomain.getCodeSource();
         URL rootJarUrl = codeSource.getLocation();
         String rootJarName = rootJarUrl.getFile();
         if (isJar(rootJarName)) {
          addJarResource(new File(rootJarUrl.getPath()));
         }
        } catch (IOException e) {
         e.printStackTrace();
        }
       }
       
    private void addJarResource(File file) throws IOException {
        JarFile jarFile = new JarFile(file);
        addURL(file.toURI().toURL());
        Enumeration<JarEntry> jarEntries = jarFile.entries();
        while (jarEntries.hasMoreElements()) {
         JarEntry jarEntry = jarEntries.nextElement();
         if (!jarEntry.isDirectory() && isJar(jarEntry.getName())) {
          addJarResource(jarEntryAsFile(jarFile, jarEntry));
         }
        }
       }
        
       @Override
       protected synchronized Class<?> loadClass(String name, boolean resolve) 
        throws ClassNotFoundException {
        try {
         Class<?> clazz = findLoadedClass(name);
         if (clazz == null) {
          clazz = findClass(name);
          if (resolve)
           resolveClass(clazz);
         }
         return clazz;
        } catch (ClassNotFoundException e) {
         return super.loadClass(name, resolve);
        }
       }
}