Launch JVM process from a Java application use Runtime.exec?

Question

I want to be able to launch a Java server process from an existing java application and monitor the stdoutput and stderror and redirect that output to a file. Is the best approach to use 'Runtime.exec' and treat the app like any other OS process or is there something more suited for new JVMs.

This is on Java 1.5

Answer 1

Instead of Runtime, you should probably use ProcessBuilder, though I don't know if something else is even more appropriate in your case (running a Java process in particular).

Answer 2

I know I am late in this thread, but in case someone needs it, in my experience, it is easier to use ANT to launch a Java application. This has the benefit of being platform independent. Here is a sample class that does that:

package com.trilliantnetworks.scheduler.quartz.test;

import java.io.File;
import java.io.PrintStream;
import org.apache.tools.ant.BuildException;
import org.apache.tools.ant.DefaultLogger;
import org.apache.tools.ant.DemuxOutputStream;
import org.apache.tools.ant.Project;
import org.apache.tools.ant.taskdefs.Echo;
import org.apache.tools.ant.taskdefs.Java;
import org.apache.tools.ant.types.Path;

public class MyLaunchTest {

public static void main(String[] args) {

    Project project = new Project();
    project.setBaseDir(new File(System.getProperty("user.dir")));
    project.init();
    DefaultLogger logger = new DefaultLogger();
    project.addBuildListener(logger);
    logger.setOutputPrintStream(System.out);
    logger.setErrorPrintStream(System.err);
    logger.setMessageOutputLevel(Project.MSG_INFO);
    System.setOut(new PrintStream(new DemuxOutputStream(project, false)));
    System.setErr(new PrintStream(new DemuxOutputStream(project, true)));
    project.fireBuildStarted();

    System.out.println("running");
    Throwable caught = null;
    try {
        Echo echo = new Echo();
        echo.setTaskName("Echo");
        echo.setProject(project);
        echo.init();
        echo.setMessage("Launching Some Class");
        echo.execute();

        Java javaTask = new Java();
        javaTask.setTaskName("runjava");
        javaTask.setProject(project);
        javaTask.setFork(true);
        javaTask.setFailonerror(true);
        javaTask.setClassname(MyClassToLaunch.class.getName());
        Path path = new Path(project, new File(System.getProperty("user.dir") + "/classes").getAbsolutePath());
        javaTask.setClasspath(path);
        javaTask.init();
        int ret = javaTask.executeJava();
        System.out.println("java task return code: " + ret);

    } catch (BuildException e) {
        caught = e;
    }
    project.log("finished");
    project.fireBuildFinished(caught);
}
}