Communicating with unix command process from java using stream

[megha joshi]

Hi all,

I want to use stream based IPC in Java. To test this I am trying to exec unix more filename command from my java code. Interesting thing is commands like ps, man, ls -l execute fine using the code below. But executing more on a big file , which requires enter input from keyboard occasionally fails. I would like to give input to this unix process from my java code..but I am not sure how to do that. The code I have so far is as follows:

  
import java.io.*;
 
public class IPCTest
{
   public static void main(String args[])
   {
      Process theProcess = null;
      BufferedReader inStream = null;
 
      System.out.println("IPCTest.main() invoked");
      int i=-1;
      // call the CSAMP1 program
      try
      {
          theProcess = Runtime.getRuntime().exec("more ViewActivity.java");
          i = theProcess.waitFor();
	  System.out.println("done");
      }
      catch(Exception e)
      {
         System.out.println("Error on exec() method");
         e.printStackTrace();  
      }
 
      // read from the called program's standard output stream
      if ( i == 0) {
      try
      {
         inStream = new BufferedReader(new InputStreamReader
                           (theProcess.getInputStream()));
	 String line;
	 while((line = inStream.readLine()) != null) {
             System.out.println(line);
	 } 
	 /*
	 InputStream output = theProcess.getInputStream();
	 System.out.println(output);
	 */
	 inStream.close();
      }
      catch(Throwable t)
      {
         t.printStackTrace();
      }
      }
 
   } // end method
 
 } // end class

[Rob Spoor]

Search for the Javaworld article "When Runtime.exec() won't". It's a must-read when working with Processes.

[megha joshi]

Thanks..I went through it though issues mentioned in the article, are not relevant for this case. Any other suggestions? Thanks again!

[Rob Spoor]

megha joshi wrote:issues mentioned in the article, are not relevant for this case.

Are you sure? Perhaps the process is being paused because its output / error buffer is full, something that is very clearly discussed in the article. Once you clear the output and error buffers it may continue again.