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

If you do decide to use Runtime, read "When Runtime.exec Won't..."

Answer 3

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);
}
}