jarrunner.java

这是一个英文版的《Java程序设计与问题解决》现在好多大学都当成教材

import java.io.IOException;
import java.net.URL;
import java.net.MalformedURLException;
import java.lang.reflect.InvocationTargetException;

/**
 * Runs a jar application from any url. Usage is 'java JarRunner url [args..]'
 * where url is the url of the jar file and args is optional arguments to
 * be passed to the application's main method.
 */
public class JarRunner {
    public static void main(String[] args) {
	if (args.length < 1) {
	    usage();
	}
	URL url = null;
	try {
	    url = new URL(args[0]);
	} catch (MalformedURLException e) {
	    fatal("Invalid URL: " + args[0]);
	}
	// Create the class loader for the application jar file
	JarClassLoader cl = new JarClassLoader(url);
	// Get the application's main class name
	String name = null;
	try {
	    name = cl.getMainClassName();
	} catch (IOException e) {
	    System.err.println("I/O error while loading JAR file:");
	    e.printStackTrace();
	    System.exit(1);
	}
	if (name == null) {
	    fatal("Specified jar file does not contain a 'Main-Class'" +
		  " manifest attribute");
	}
	// Get arguments for the application
	String[] newArgs = new String[args.length - 1];
	System.arraycopy(args, 1, newArgs, 0, newArgs.length);
	// Invoke application's main class
	try {
	    cl.invokeClass(name, newArgs);
	} catch (ClassNotFoundException e) {
	    fatal("Class not found: " + name);
	} catch (NoSuchMethodException e) {
	    fatal("Class does not define a 'main' method: " + name);
	} catch (InvocationTargetException e) {
	    e.getTargetException().printStackTrace();
	    System.exit(1);
	}
    }

    private static void fatal(String s) {
	System.err.println(s);
	System.exit(1);
    }

    private static void usage() {
	fatal("Usage: java JarRunner url [args..]");
    }
}