Re: Execute OS command

Nigel Wade <>
Thu, 13 Sep 2007 10:11:23 +0100
Earl Lewis wrote:

You java gurus probably hate it when a posting starts like this, but
here goes anyway. Sorry, in advance!

Disclaimer: I'm not a java guru. I know how to spell it and I've
written some basic OO stuff. I now have a real problem that I'm trying
to solve but have no idea how best to implement it.

Here's the situation. I have a small java routine (in Oracle) that
executes an operating system command. Here's that code:

public class Host {
  public static void executeCommand(String command) {
    try {
      String[] finalCommand;
      if (isWindows()) {
        finalCommand = new String[4];
        // Use the appropriate path for your windows version.
        finalCommand[0] = "C:\\windows\\system32\\cmd.exe"; //
Windows XP/2003
        //finalCommand[0] = "C:\\winnt\\system32\\cmd.exe"; //
Windows NT/2000
        finalCommand[1] = "/y";
        finalCommand[2] = "/c";
        finalCommand[3] = command;
      else {
        finalCommand = new String[3];
        finalCommand[0] = "/bin/sh";
        finalCommand[1] = "-c";
        finalCommand[2] = command;

      final Process pr = Runtime.getRuntime().exec(finalCommand);

      new Thread(new Runnable(){
        public void run() {
          BufferedReader br_in = null;
          try {
            br_in = new BufferedReader(new
            String buff = null;
            while ((buff = br_in.readLine()) != null) {
              System.out.println("Process out :" + buff);
              try {Thread.sleep(100); } catch(Exception e) {}
          catch (IOException ioe) {
            System.out.println("Exception caught printing process
          finally {
            try {
            } catch (Exception ex) {}

      new Thread(new Runnable(){
        public void run() {
          BufferedReader br_err = null;
          try {
            br_err = new BufferedReader(new
            String buff = null;
            while ((buff = br_err.readLine()) != null) {
              System.out.println("Process err :" + buff);
              try {Thread.sleep(100); } catch(Exception e) {}
          catch (IOException ioe) {
            System.out.println("Exception caught printing process
          finally {
            try {
            } catch (Exception ex) {}
    catch (Exception ex) {

  public static boolean isWindows() {
(System.getProperty("").toLowerCase().indexOf("windows") != -1)
      return true;
      return false;


What I want to do is put a timer in this code that will only allow the
command to attempt to run for a set amount of time, and when that time
elapses the program will decide that the command isn't going to work
and it quits with an error message.

The way I understand the documentation, as the code is written right
now (with the pr.waitFor(); line) it will wait for the process (in
this case an OS command) to complete before the code will continue.
That seems to bear out in my testing so far.

I've seen also in the javadocs where you can call Thread.join(50000);
or something similar, to join the running thread and if it doesn't
complete in the specified time that it will kill the thread. Is this
the right approach to solving this problem? Is the problem even clear?
Any suggestions about how to do this and where to put the suggested
code snippets will be greatly appreciated. Thank you.



I believe there is a flaw in the logic in the above program.

You call Process.waitFor() before you start the threads which read the process's
standard output/error channels. If the process generates a lot of output, such
that either the output or error channel fills and blocks the process, the
waitFor() will not return. The threads to read that output, which should
prevent the process from blocking, haven't been started yet. Start the threads
to read the process output *before* you invoke Process.waitFor().

This may prevent you from needing to terminate if the process doesn't complete
in a fixed time.

Nigel Wade, System Administrator, Space Plasma Physics Group,
            University of Leicester, Leicester, LE1 7RH, UK
E-mail :
Phone : +44 (0)116 2523548, Fax : +44 (0)116 2523555

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