Question

Why I get the output of the process after the process has terminated? I need to get the process output “live”, while the process is running and not after the process has terminated. I would like to run a process like a jboss, which is logging on the standard output, so I need that information in time, and not after the process has terminated. Thank you for answers.

Here is my code:

        try {
        process = processBuilder.start();
        processOutput = process.getOutputStream();
        processInput = process.getInputStream();
        processReader = new BufferedReader(new InputStreamReader(
                processInput));
        processWriter = new BufferedWriter(new OutputStreamWriter(
                processOutput));

        while ((line = processReader.readLine()) != null) {
            System.out.println(line);
          }
        processReader.close();

    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

Extension:

So I would like to run an external program from an eclipse plug-in with a button. When I click to the button, the program start and the output of the external program will go back to the console. When I click to the stop, the program stops. So here is how I make the instance of the process builder. And I made an example class to test the process builder without start the whole plugin project in every modification.

Here is my process builder instance which is implements the Runnable:

@Override
public void run() {
    List<String> command = new ArrayList<String>();
    command.add(serverPath);
    command.add(String.valueOf(count));
    command.add(filePath);
    processBuilder = new ProcessBuilder(command);
    processBuilder.redirectErrorStream(true);

    try {
        process = processBuilder.start();
        processOutput = process.getOutputStream();
        processInput = process.getInputStream();
        processReader = new BufferedReader(new InputStreamReader(
                processInput));
        processWriter = new BufferedWriter(new OutputStreamWriter(
                processOutput));

        System.out.println(process.waitFor());
        while ((line = processReader.readLine()) != null) {
            System.out.println(line);

        }
        processReader.close();

    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}

The parameters are come in the constructor. And here is the instantiation:

public static void main(String[] args) throws Exception

{

 SimulationProcess smp = new SimulationProcess(count, "file",
            "program_name");
    smp.run();

}

Answer 1

There are a few things you can try to resolve your issue:

a) Make a test program and run it with your above code to ensure you can read it properly. For example:

public static void main(String[] args) {
  for(;;) {
    try {
      Thread.sleep(5000);
      System.out.println("Test output");
    } catch(InterruptedException e) {
      // Ignore
    }

  }
}

b) Make sure you are handling the process’ error stream – the process can lock up if you do not handle the error stream. Look at this site for a tutorial on the things to avoid while using Java’s ProcessBuilder or Runtime.exec() – it includes an implementation of a StreamGobbler that will throw away all data on a stream you don’t care about.

c) Try using System.out.flush() – it may be that your output is being buffered.

EDIT: Thanks for the update. Your problem is here:

System.out.println(process.waitFor()); // Waits for the process to exit.
while ((line = processReader.readLine()) != null) {
    System.out.println(line);
}

If you remove the waitFor() it will keep printing until the stream closes. The stream should only close if the process dies. You should put the waitFor() after the loop?