How to stop threads, process, streams when closing a (internal) JFrame?

Question

Dear all,
I read a Javaworld article about Runtime.exec(), which will output the process outputs and error outputs to either a file or System.out. Now I want to practice it by outputing the process output/error to a Swing JTextArea. It works fine if the process ends successfully.
My problem is that I want to stop all the output threads and clear all the streams when user click close JFrame button before the process finished. The code is shown below. Note that this frame is poped up by a click from another main frame. ( it is not exiting the main Swing application). This happened when I want to kill a process when it is running.
I tried to implements a WindowListener and add
public void windowClosing(WindowEvent e) to the JFrame.
Inside this method I used process.destroy() and errorGobbler = null, outputGobbler = null, or outputGobbler.interrupt(), errorGobbler.interrupt(). But all these seems does not work. Sometimes thread was not stopped, sometimes process was not destroyed (because the stream was still print out something), sometimes the error stream was not successfully closed - by printing out interruptted by user error message.
How can I make sure all the underlying streams and threads, including the PrintStream in StreamGobbler class are closed?
Again this Frame could be a Dialog or InternalFrame, i.e, when I close the frame, the main frame does not exit!
import java.util.*;
import java.io.*;
class StreamGobbler extends Thread
    InputStream is;
    String type;
    OutputStream os;
    StreamGobbler(InputStream is, String type, JTextArea out)
        this(is, type, null, out);
    StreamGobbler(InputStream is, String type, OutputStream redirect, JTextArea out)
        this.is = is;
        this.type = type;
        this.os = redirect;
    public void run()
        try
            PrintWriter pw = null;
            if (os != null)
                pw = new PrintWriter(os);
            InputStreamReader isr = new InputStreamReader(is);
            BufferedReader br = new BufferedReader(isr);
            String line=null;
            while ( (line = br.readLine()) != null)
                if (pw != null)
                    pw.println(line);
                out.append(type + ">" + line);   
            if (pw != null)
                pw.flush();
        } catch (IOException ioe)
            ioe.printStackTrace(); 
public class Test extends JFrame
    private JTextArea output;
    private StreamGobbler outputGobbler;
    private StreamGobbler errorGobbler;
    public Test (String file)
        super();
        output = new JTextArea();
        try
            FileOutputStream fos = new FileOutputStream(file);
            Runtime rt = Runtime.getRuntime();
            Process proc = rt.exec("java jecho 'Hello World'");
            errorGobbler = new
                StreamGobbler(proc.getErrorStream(), "ERROR", out);           
            outputGobbler = new
                StreamGobbler(proc.getInputStream(), "OUTPUT", fos, out);
            errorGobbler.start();
            outputGobbler.start();
            int exitVal = proc.waitFor();
            output.append("ExitValue: " + exitVal);
            fos.flush();
            fos.close();       
        } catch (Throwable t)
            t.printStackTrace();
     setSize(400,400);
     show();
}Thanks !

Answer 1

Thread.interrupt() doesn't stop a thread. You'll have to read the API for more specifics. You could use something like interrupt to force interruption of the thread for the reason of checking the terminating case though. I believe you would want to use this in the case where operations can take a long time.
Setting your reference to the thread to be null won't stop the thread since it's running. You just lose your reference to it.
I believe once the thread stops running your streams will be closed, but possibly not cleanly. Someone who has more knowledge of threads might be able to answer this better, but I would generally say clean up after yourself especially if you are writting out data.