Multiple Java apps running in one VM

Question

I have one VM that runs one application with GUI, database. It also spawns another VM to run more apps through Sockets.
Is there a way to run several Java apps within a single VM? If so, I can get rid of those interprocess communication stuff and make things easier.
Thanks in advance.
Lee

Answer 1

Yes you can do what to want to do. It is actually very benificail. Take a look at this article:
http://java.sun.com/docs/books/performance/1st_edition/html/JPClassLoading.fm.html#24732
here is code to do it as well:
package com.ist.system;
import com.ist.util.LogMsg;
import java.io.IOException;
import java.io.OutputStream;
import java.lang.reflect.Method;
import java.net.InetAddress;
import java.net.Socket;
* This class was pulled from:
* http://java.sun.com/docs/books/performance/1st_edition/html/JPClassLoading.fm.html#24732
* It was written to provide the ability to launch many applications in the
* same JVM.  By doing this, it will save on system resources like RAM.  When
* the <code>launch</code> method is called, it will check to see if there is a
* VM already running.  If there is, it will launch the new application in the
* currently running VM.  If there isn't, it will create a process that will
* keep a VM alive until there are no more applications running.  Once there are
* no more applications running, this service will System.exit. 
public class Launcher {
    static final int socketPort = 9876;
     * This method will launch a new instance of the passed in className
     * in an already running JVM if one is already running.  If one is not
     * running, this application will create one.
     * @param className the class which you wish to launch
    public void launch(String className) {
        LogMsg.shortDebug("Trying to launch: " + className);
        Socket s = findService();
        if (s != null) {
            LogMsg.shortDebug("Launcher found service");
            try {
                OutputStream oStream = s.getOutputStream();
                byte[] bytes = className.getBytes();
                oStream.write(bytes.length);
                oStream.write(bytes);
                oStream.close();
                LogMsg.shortDebug(className);
            } catch (IOException e) {
                LogMsg.warn("Launcher couldn't talk to service");
        } else {
            LogMsg.event("Starting new service");
            Launcher.go(className);
            Thread listener = new ListenerThread();
            listener.start();
            LogMsg.shortDebug("Started service listener");
    protected Socket findService() {
        try {
            Socket s = new Socket(InetAddress.getLocalHost(),
            socketPort);
            return s;
        } catch (IOException e) {
            // couldn't find a service provider
            return null;
    public static synchronized void go(final String className) {
        LogMsg.shortDebug("Launcher running a " + className);
        Thread thread = new Thread() {
            public void run() {
                try {
                    Class clazz = Class.forName(className);
                    Class[] argsTypes = {String[].class};
                    Object[] args = {new String[0]};
                    Method method = clazz.getMethod("main", argsTypes);
                    method.invoke(clazz, args);
                } catch (Exception e) {
                    LogMsg.shortDebug("Launcher coudn't run the " + className);
        }; // end thread sub-class
        thread.start();
        runningPrograms++;
    static int runningPrograms = 0;
     * All programs wishing to exit should call this method and NOT
     * use System.exit.  Calling System.exit will kill all the applications
     * running in this VM.
    public static synchronized void programQuit() {
        runningPrograms--;
        if (runningPrograms <= 0) {
            System.exit(0);
    public static void main(String[] args) {
        LogMsg.setupTraceLevel();
        Launcher l = new Launcher();
        l.launch(args[0]);
}