Executing a different Jar file from another java program

Question

As a part of my program, I have a connections manager that receives a connection from a client, and then gives the client a port number and a password to use to connect. A this point the manager needs to call the jar file I have to handle this connections, with a few arguments, and continue on,( ignoring what the other program is doing).

My problem has been with executing the jar file. I've looked up similar question's and have tried using a process builder and using Runtime.exec. I moved around the jar file, and checked it's permissions. It just refuse to work from another java program, but works perfectly from the command line. Here's an example of one of my test runs.

package test;

import java.io.*;

public class Main {
    public static void main (String [] args ) throws IOException, ClassNotFoundException, InterruptedException {
        Process p = Runtime.getRuntime().exec("java -jar \'/home/ryan/CytoscapeInterface.jar" +
        "\' arg1 arg2");
        //Process builder way
        /*ProcessBuilder pb = new ProcessBuilder("/home/ryan/CytoscapeInterface.jar",
           "-jar", "CytoscapeInterface.jar", "agr1", "arg2");
        pb.redirectErrorStream();
        Process p = pb.start();*/
        BufferedInputStream bis = new BufferedInputStream(p.getErrorStream());
        synchronized (p) { p.waitFor(); }
        System.out.println(p.exitValue());//its 1 for runtime, 2 for process Builder
        int read = bis.available();
        //had a loop, found out I just needed to go through once
        byte[] b = new byte [read];
        bis.read(b);
        read = bis.available();
        bis.close();
        FileOutputStream fos = new FileOutputStream (new File("/home/ryan/Desktop/FileTest.txt"));
        fos.write(b);//Writes error file
        fos.close();
    }
}

waitFor returns 1 for runtime and 2 for the builder. The error output for runtime is "Unable to access jarfile '/home/ryan/CytoscapeInterface.jar'. While using the builder gives a couple lines of error that had some weird characters, the first error was command not found.

JSS · Accepted Answer · 2011-07-06 16:43:31Z

5

I have suceessfully tested the scenario and I can execute the jar file with in java programme (without setting the classpath).

Can you make sure that you have added Manifest file in the jar which has Main-Class attribute.

My steps and output:

Created Mainfest file with the following line: Main-Class: com.test.TestJSSJar
Created Test Java program:

package com.test;



public class TestJSSJar extends Object {

    public static void main(String args[]) {
        System.out.println("Hi! I'm in the jar");
        System.out.println("Arg:" + args[0]);
    }
}

3.Package the jar (moved to temp folder): jar cvfm jss.jar manifest.txt com

4.Write test program:

import java.io.BufferedInputStream;
import java.io.IOException;

public class TestJSS extends Object {

    static int i = 0;

    public static void main(String args[]) throws IOException, InterruptedException {
        System.out.println("Calling jar");
        Process p = Runtime.getRuntime().exec("java -jar /temp/jss.jar arg1 arg2");
        BufferedInputStream bis = new BufferedInputStream(p.getInputStream());
        synchronized (p) {
            p.waitFor();
        }
        System.out.println(p.exitValue());
        int b=0;
        while((b=bis.read()) >0){

            System.out.print((char)b);    
        }        
        System.out.println("");
        System.out.println("Called jar");
    }
}

5.Output

Calling jar
0
Hi! I'm in the jar
Arg:arg1

Called jar

edited Jul 6, 2011 at 16:43

answered Jul 6, 2011 at 16:37

JSS

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3 Comments

Ryan Over a year ago

Tried, same result, "Unable to access jar file". Only weird part was when I used Main, package that the main class is in, instead of com it said "Main: no such file or directory". Still created the jar file in my home dir. Also checked permissions.

JSS Over a year ago

@Ryan - Can you please try following steps: 1. Check "Main" directory exist in the path where you creating the jar. 2. Don't use single quote when specifying jar path (as per ur original post, see how I have done it). 3. Also check if you can execute same command on the command prompt (without changaing any path values)

Ryan Over a year ago

Well now I feel stupid, removed the single quotes and it worked... swear I saw them in an example... Thanks

Jeesmon · Accepted Answer · 2011-07-06 16:02:51Z

0

Include jar in the classpath and call the main method of the Main-class of the jar from your main.

Suppose Main-class of CytoscapeInterface.jar is JarMain.class (You can look it up in META-INF of CytoscapeInterface.jar), then from your program, call it like this:

JarMain.main(new String[]{"arg1", "arg2"});

You can also call it from a new Thread so that you can continue with your program.

        new Thread(
        new Runnable() {
            public void run() {
                try {
                    JarMain.main(new String[]{"arg1", "arg2"});
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }).start();

answered Jul 6, 2011 at 16:02

Jeesmon

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2 Comments

Ryan Over a year ago

Never changed the classpath before, there are examples online but they never seem to show where you specify which program you want to have the different classpath. Is there an easy way to do it in netbeans?

Ryan Over a year ago

Tried using netbeans, added it using projectproperties.libraries.run. Same error

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