JarClassLoader.java Source code

Introduction

Here is the source code for JarClassLoader.java

Source

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);
    }
}