[java] Execute another jar in a Java program

I had written several simple java applications named as A.jar, B.jar.

Now i want to write a GUI java program so that user can press button A to execute A.jar and button B to execute B.jar.

Also i want to output the run-time process detail in my GUI program.

Any suggestion?

If the jar's in your classpath, and you know its Main class, you can just invoke the main class. Using DITA-OT as an example:

import org.dita.dost.invoker.CommandLineInvoker;
....
CommandLineInvoker.main('-f', 'html5', '-i', 'samples/sequence.ditamap', '-o', 'test')

Note this will make the subordinate jar share memory space and a classpath with your jar, with all the potential for interference that can cause. If you don't want that stuff polluted, you have other options, as mentioned above - namely:

• create a new ClassLoader with the jar in it. This is more safe; you can at least isolate the new jar's knowledge to a core classloader if you architect things with the knowledge that you'll be making use of alien jars. It's what we do in my shop for our plugins system; the main application is a tiny shell with a ClassLoader factory, a copy of the API, and knowledge that the real application is the first plugin for which it should build a ClassLoader. Plugins are a pair of jars - interface and implementation - that are zipped up together. The ClassLoaders all share all the interfaces, while each ClassLoader only has knowledge of its own implementation. The stack's a little complex, but it passes all tests and works beautifully.
• use Runtime.getRuntime.exec(...) (which wholly isolates the jar, but has the normal "find the application", "escape your strings right", "platform-specific WTF", and "OMG System Threads" pitfalls of running system commands.

The following works by starting the jar with a batch file, in case the program runs as a stand alone:

public static void startExtJarProgram(){
        String extJar = Paths.get("C:\\absolute\\path\\to\\batchfile.bat").toString();
        ProcessBuilder processBuilder = new ProcessBuilder(extJar);
        processBuilder.redirectError(new File(Paths.get("C:\\path\\to\\JavaProcessOutput\\extJar_out_put.txt").toString()));
        processBuilder.redirectInput();
        try {
           final Process process = processBuilder.start();
            try {
                final int exitStatus = process.waitFor();
                if(exitStatus==0){
                    System.out.println("External Jar Started Successfully.");
                    System.exit(0); //or whatever suits 
                }else{
                    System.out.println("There was an error starting external Jar. Perhaps path issues. Use exit code "+exitStatus+" for details.");
                    System.out.println("Check also C:\\path\\to\\JavaProcessOutput\\extJar_out_put.txt file for additional details.");
                    System.exit(1);//whatever
                }
            } catch (InterruptedException ex) {
                System.out.println("InterruptedException: "+ex.getMessage());
            }
        } catch (IOException ex) {
            System.out.println("IOException. Faild to start process. Reason: "+ex.getMessage());
        }
        System.out.println("Process Terminated.");
        System.exit(0);
    }

In the batchfile.bat then we can say:

@echo off
start /min C:\path\to\jarprogram.jar

Hope this helps:

public class JarExecutor {

private BufferedReader error;
private BufferedReader op;
private int exitVal;

public void executeJar(String jarFilePath, List<String> args) throws JarExecutorException {
    // Create run arguments for the

    final List<String> actualArgs = new ArrayList<String>();
    actualArgs.add(0, "java");
    actualArgs.add(1, "-jar");
    actualArgs.add(2, jarFilePath);
    actualArgs.addAll(args);
    try {
        final Runtime re = Runtime.getRuntime();
        //final Process command = re.exec(cmdString, args.toArray(new String[0]));
        final Process command = re.exec(actualArgs.toArray(new String[0]));
        this.error = new BufferedReader(new InputStreamReader(command.getErrorStream()));
        this.op = new BufferedReader(new InputStreamReader(command.getInputStream()));
        // Wait for the application to Finish
        command.waitFor();
        this.exitVal = command.exitValue();
        if (this.exitVal != 0) {
            throw new IOException("Failed to execure jar, " + this.getExecutionLog());
        }

    } catch (final IOException | InterruptedException e) {
        throw new JarExecutorException(e);
    }
}

public String getExecutionLog() {
    String error = "";
    String line;
    try {
        while((line = this.error.readLine()) != null) {
            error = error + "\n" + line;
        }
    } catch (final IOException e) {
    }
    String output = "";
    try {
        while((line = this.op.readLine()) != null) {
            output = output + "\n" + line;
        }
    } catch (final IOException e) {
    }
    try {
        this.error.close();
        this.op.close();
    } catch (final IOException e) {
    }
    return "exitVal: " + this.exitVal + ", error: " + error + ", output: " + output;
}
}

.jar isn't executable. Instantiate classes or make call to any static method.

EDIT: Add Main-Class entry while creating a JAR.

>p.mf (content of p.mf)

Main-Class: pk.Test

>Test.java

package pk;
public class Test{
  public static void main(String []args){
    System.out.println("Hello from Test");
  }
}

Use Process class and it's methods,

public class Exec
{
   public static void main(String []args) throws Exception
    {
        Process ps=Runtime.getRuntime().exec(new String[]{"java","-jar","A.jar"});
        ps.waitFor();
        java.io.InputStream is=ps.getInputStream();
        byte b[]=new byte[is.available()];
        is.read(b,0,b.length);
        System.out.println(new String(b));
    }
}

If I understand correctly it appears you want to run the jars in a separate process from inside your java GUI application.

To do this you can use:

// Run a java app in a separate system process
Process proc = Runtime.getRuntime().exec("java -jar A.jar");
// Then retreive the process output
InputStream in = proc.getInputStream();
InputStream err = proc.getErrorStream();

Its always good practice to buffer the output of the process.

If you are java 1.6 then the following can also be done:

import javax.tools.JavaCompiler; 
import javax.tools.ToolProvider; 

public class CompilerExample {

    public static void main(String[] args) {
        String fileToCompile = "/Users/rupas/VolatileExample.java";

        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();

        int compilationResult = compiler.run(null, null, null, fileToCompile);

        if (compilationResult == 0) {
            System.out.println("Compilation is successful");
        } else {
            System.out.println("Compilation Failed");
        }
    }
}