Re: Runtime.Exec and windows batch file

Knute Johnson <>
Tue, 17 Oct 2006 17:09:50 -0700
<vfeZg.61$yy2.12@newsfe11.phx> wrote: wrote:

Gordon Beaton wrote:

On 17 Oct 2006 11:56:42 -0700, wrote:

Hi Im trying to run an Exec(Blah.bat) however it seems to be
freezing for some reason if the exec returns errors then the Exec
does not freez however if run the file and all i get is output it
just freezes.

The following line will attempt to read one line from each of the
streams alternately:

while ( (line = br.readLine()) != null && (line2 = bri.readLine()) !=

As long as both streams have something to read, the loop progresses.
As soon as one stream has nothing, readLine() blocks waiting for it.

There are essentially two ways to do this correctly:

- create a second Thread to read from one of the streams, and read
  from the other one in the original Thread
- use ProcessBuilder to combine the two streams, so you really can
  read from both at the same time.


[ don't email me support questions or followups ]
g o r d o n + n e w s @ b a l d e r 1 3 . s e

Hmmm .....

So do something of this nature:

have a class

public class ReadThread implements Runnable {
BufferedReader reader;

public ReadThread(BufferedReader br) {
       reader = br;

public BufferedReader getReader() {
       return reader;

public void setNumber(BufferedReader br) {
    reader = br;

public void run()
String line2 = null;

try {

    while ( (line2 = reader.readLine()) != null)
                 System.out.println("Error:" + line2 + ":Error");
} catch (IOException e) {
// TODO Auto-generated catch block

and from my code instead of having that ugly if statment do

MyThread Error = new MyThread(br);
MyThread Outp = new MyThread(bri);;;

This seems to Block when I run it

It won't either as you are not creating new threads you are just calling
the run method so the first one blocks your execution.

Take a look at the following code. I wrote this because I was doing a
lot of execing for a while and wanted to simplify the coding. I'm not
sure that it exactly did what I wanted but it should give you some idea
how to code these things.

// ProcessControl


public class ProcessControl {
     private Process process;

     public ProcessControl(String... args) throws IOException {
         ProcessBuilder builder = new ProcessBuilder(args);
         process = builder.start();

     public void handleInput(final InputStream is) {
         Runnable r = new Runnable() {
             public void run() {
                 BufferedReader br = null;
                 try {
                     InputStreamReader isr = new InputStreamReader(is);
                     br = new BufferedReader(isr);
                     String string = null;
                     while ((string = br.readLine()) != null)
                 } catch (IOException ioe) {
                     System.out.println("ProcessControl.handleInput(): "
+ ioe);
                 } finally {
                     if (br != null)
                         try {
                         } catch (IOException ioe) {
         new Thread(r).start();

     public void handleInput() {

     public void handleError() {

     public Process getProcess() {
         return process;

     public OutputStream getOutputStream() {
         return process.getOutputStream();

     public InputStream getInputStream() {
         return process.getInputStream();

     public InputStream getErrorStream() {
         return process.getErrorStream();

     public int waitFor() throws InterruptedException {
         return process.waitFor();

     public static void main(String[] args) {
         try {
             ProcessControl pc = new ProcessControl(args);
         } catch (Exception e) {

And here is a program you can use to test the stdin and stderr.

public class test {
     public static void main(String[] args) {


Knute Johnson
email s/nospam/knute/

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