Run External application without Exiting main application

Question

Hi,
I am trying to implement a function that executes the external program from within my java application. I am using windows xp. I had googled for this and found some code but so far I am able to run the application in a condition if my main application exits. Instead I want to run the application without exiting my main application. How can I do that:
Code I am using is:
========================
try{
Runtime.getRuntime().exec("external program");
System.exit(0);
catch (Exception err){
err.printStackTrace();
System.exit(-1);
=========================
my problem is I cannot run the external program without the line "System.exit(0)". If I remove that line, the external program only starts after I exit my main java application. Is there a way to run the external application without leaving the main application?
By the way I am using the latest version of JDK 6 update 2 and Netbeans 5.5.1
Thanks

Answer 1

I tried and I tried and I couldn't make the same problem occur unless I specfically had a long task execute BEFORE calling the runtime command. See the code below:
I tried a bunch of things, including having a GUI run before the Runtime call, after the runtime call. Neither affected the movie from being played.
I tried with different versions of the runtime command, none of it made a problem.
I tried running the application with a long task that would keep the main thread busy for a while AFTER I launched mplayer - no problem.
The only thing that made the app work the way you describe was when I built the long task that keeps the main thread active for a while BEFORE I launched mplayer (which is the state of the code as I pasted it below).
So my guess is that you have a single threaded application and you add the call to mplayer at the very end of your program's execution - thus it doesn't get called until the last thing. My suggestions:
1) Move the call to the Start of your code, not the end
2) Move your other work to a new thread so that it can be kicked off without holding the main thread in check.
package movies;
import inheritance.BaseWindow;
import java.util.*;
import java.io.*;
class StreamGobbler extends Thread
    InputStream is;
    String type;
    OutputStream os;
    StreamGobbler(InputStream is, String type)
        this(is, type, null);
    StreamGobbler(InputStream is, String type, OutputStream redirect)
        this.is = is;
        this.type = type;
        this.os = redirect;
    public void run()
        try
            PrintWriter pw = null;
            if (os != null)
                pw = new PrintWriter(os);
            InputStreamReader isr = new InputStreamReader(is);
            BufferedReader br = new BufferedReader(isr);
            String line=null;
            while ( (line = br.readLine()) != null)
                if (pw != null)
                    pw.println(line);
                System.out.println(type + ">" + line);   
            if (pw != null)
                pw.flush();
        } catch (IOException ioe)
            ioe.printStackTrace(); 
public class MyMainClass
    public static void main(String args[]) throws InterruptedException
         //This is just a GUI as a test
        BaseWindow bw = new BaseWindow();
        bw.show();
        //Keep App Running for a while
        int count = 0;
        while (count < 200) {
             Thread.sleep(20);
             count++;
             System.err.println(count);
        if (args.length != 1)
            System.out.println("USAGE java movies.MyMainClass \"<movie to play>\"");
            System.exit(1);
        try
            Runtime rt = Runtime.getRuntime();
            //String[] cmds = new String[] { "cmd", "/c", "C:\\Mplayer\\mplayer.exe", args[0]};
            //String[] cmds = new String[] { "C:\\Mplayer\\mplayer.exe", args[0]};
            //Process proc = rt.exec(cmds);
            Process proc = rt.exec("C:\\Mplayer\\mplayer.exe "+args[0]);
            // any error message?
            StreamGobbler errorGobbler = new
                StreamGobbler(proc.getErrorStream(), "ERROR");           
            // any output?
            StreamGobbler outputGobbler = new
                StreamGobbler(proc.getInputStream(), "OUTPUT");
            // kick them off
            errorGobbler.start();
            outputGobbler.start();
            //Keep App Running for a while
//            int count = 0;
//          while (count < 2000000) {
//                 Thread.sleep(200);
//                 count++;
//                 System.err.println(count);
            // any error???
            int exitVal = proc.waitFor();
            System.out.println("ExitValue: " + exitVal);
        } catch (Throwable t)
            t.printStackTrace();
}I will restate myself:
"I was not able to repeat the problem, except as described, as long as I took the hints mentioned in the article I posted into account and actually put them into action."
Of course, as soon as I ignored those hints, I was able to reproduce the error described above quite easily in all the different tests I made... But I guess the OP implemented those fixes, right? He did say he read the article...
Message was edited by:
stevejluke