How do i make a gui to cancel a process

Question

Hello,
I am trying make a traceroute in Java. Since i didn't an API to make things easier on me. I have a class 'Traceroute' like this:
public class Traceroute {
    OSstuff OS = new OSstuff();
    Process trace;
    public Traceroute(){
    public List<ResultLine> traceroute(String host,int hops,int timeout){
        List<ResultLine> results = new LinkedList<ResultLine>();
    try {
        if (OS.isWindows()){
            Process trace = Runtime.getRuntime().exec("tracert -h " + hops + " -d -w " + timeout + " " + host);
            BufferedReader br = new BufferedReader(new InputStreamReader(trace.getInputStream()));
            String line;
            while((line = br.readLine()) != null) {    
              if(!line.startsWith("  ")) continue;
              //if(line.length() < 32) continue;
               StringTokenizer st = new StringTokenizer(line);
                if(st.countTokens() != 8 ) {
//                    ResultLine aux = new ResultLine();    //FIXME:
//                    results.add(aux);
                    return null;
               String[] tempos = new String[3];
                for(int i = 0; i < 3; i++){
                    st.nextToken();
                    tempos[i] = st.nextToken();
               st.nextToken();
               //String gate = st.nextToken();
               InetAddress gate = InetAddress.getByName(st.nextToken());
              ResultLine tmp = new ResultLine(gate,tempos);
              results.add(tmp);
        if (OS.isMac() || OS.isLinux()){
            Process trace = Runtime.getRuntime().exec(new String[]{"traceroute", "-m", "30", "-n", "-w", "2", host});
            BufferedReader br = new BufferedReader(new InputStreamReader(trace.getInputStream()));
            String line;
            while((line = br.readLine()) != null) {
              if(line.indexOf("*") != -1) continue;
              //final String ip = line.substring(4, line.indexOf(" ", 4)).trim();
              //results.add(ip);
        if (OS.OStype==OS.OTHER){
            return null;
    } catch (Exception e) {
          e.printStackTrace();
          return null;
        return results;
    public void kill(){
        trace.destroy();
}And calling the traceroute method in my GUIMain class when the "Traceroute" button is pressed, here is the event code:
    private void runButtonActionPerformed(java.awt.event.ActionEvent evt) {
        //TODO
        List<ResultLine> res;
        resultArea.setText("");
        cancelButton.setEnabled(true);
            if (targetField.getText().isEmpty())
                targetField.setText("localhost");
        res = TR.traceroute(targetField.getText(), Settings.hops, Settings.waitTime);
            if (res == null)
                resultArea.append("Error");
        StringBuilder s = new StringBuilder();
            for(ResultLine r : res){
                s.append(r.toString());
                s.append("\n");
        resultArea.setText(s.toString());
        cancelButton.setEnabled(false);   
}As it is, when the traceroute button is mpressed the program waits for the process to end and you never get to cancel the trace.
I would like help in creating a new thread (i think that this is what i need) just to run the trace process and kill the thread when either it finishes or the stop button is pressed.
PS, if some one can help me with the //FIXME on the traceroute class i would appreciate it. When ever the request exceeds the wait time the results list comes back 'null'
PS#2: I am still working on the Mac OS and Linux parts, they still need parametrization and parsing.
Edited by: Forkaster on Dec 1, 2007 11:35 AM

Answer 1

Oh, I didn't notice that it was another example of the most recurring question on Java GUI! Here's the idiom:
private void runButtonActionPerformed(java.awt.event.ActionEvent evt) {
  final List<ResultLine> res;
  resultArea.setText("");
  cancelButton.setEnabled(true);
  if (targetField.getText().isEmpty()){
    targetField.setText("localhost");
  Thread t = new Thread(new Runnable(){
    public void run(){
      String str = "";
      res = TR.traceroute
       (targetField.getText(), Settings.hops, Settings.waitTime);
      if (res == null){
        str = "Error";
      else{
        StringBuilder s = new StringBuilder();
        for (ResultLine r : res){
          s.append(r.toString());
          s.append("\n");
        str = s.toString();
      SwingUtilities.invokeLater(new Runnable(){
        public void run(){
          resultArea.setText(str);
          cancelButton.setEnabled(false);
  t.start();
}