Runs a jar application from any url : Class Loader « Reflection « Java Tutorial

1. Java Tutorial
2. Reflection
3. Class Loader

import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.net.JarURLConnection;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.jar.Attributes;
class JarClassLoader extends URLClassLoader {
  private URL url;

  public JarClassLoader(URL url) {
    super(new URL[] { url });
    this.url = url;
  }

  public String getMainClassName() throws IOException {
    URL u = new URL("jar", "", url + "!/");
    JarURLConnection uc = (JarURLConnection) u.openConnection();
    Attributes attr = uc.getMainAttributes();
    return attr != null ? attr.getValue(Attributes.Name.MAIN_CLASS) : null;
  }

  public void invokeClass(String name, String[] args) throws ClassNotFoundException,
      NoSuchMethodException, InvocationTargetException {
    Class c = loadClass(name);
    Method m = c.getMethod("main", new Class[] { args.getClass() });
    m.setAccessible(true);
    int mods = m.getModifiers();
    if (m.getReturnType() != void.class || !Modifier.isStatic(mods) || !Modifier.isPublic(mods)) {
      throw new NoSuchMethodException("main");
    }
    try {
      m.invoke(null, new Object[] { args });
    } catch (IllegalAccessException e) {

    }
  }

}
public class JarRunner {
    public static void main(String[] args) throws Exception {
        URL url = new URL(args[0]);
        JarClassLoader cl = new JarClassLoader(url);
        String name = null;
            name = cl.getMainClassName();
        if (name == null) {
            fatal("Specified jar file does not contain a 'Main-Class'" +
                  " manifest attribute");
        }
        String[] newArgs = new String[args.length - 1];
        System.arraycopy(args, 1, newArgs, 0, newArgs.length);
            cl.invokeClass(name, newArgs);
    }

    private static void fatal(String s) {
        System.err.println(s);
    }
}