Redirect stdin and stdout in Java

by

You’ve attempted to write to the output stream before you attempt to listen on the input stream, so it makes sense that you’re seeing nothing. For this to succeed, you will need to use separate threads for your two streams.

i.e.,

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.Scanner;

public class Foo {
   public static void main(String[] args) throws IOException {
      Process cmd = Runtime.getRuntime().exec("cmd.exe");

      final InputStream inStream = cmd.getInputStream();
      new Thread(new Runnable() {
         public void run() {
            InputStreamReader reader = new InputStreamReader(inStream);
            Scanner scan = new Scanner(reader);
            while (scan.hasNextLine()) {
               System.out.println(scan.nextLine());
            }
         }
      }).start();

      OutputStream outStream = cmd.getOutputStream();
      PrintWriter pWriter = new PrintWriter(outStream);
      pWriter.println("echo Hello World");
      pWriter.flush();
      pWriter.close();
   }
}

And you really shouldn’t ignore the error stream either but instead should gobble it, since ignoring it will sometimes fry your process as it may run out of buffer space.

More Related Contents:

  1. Running external program with redirected stdin and stdout from Java
  2. How to redirect system.out.print statements to web page in JSP
  3. Killing a process using Java
  4. Starting a process in Java?
  5. How can I “intercept” Ctrl+C in a CLI application?
  6. log4j redirect stdout to DailyRollingFileAppender
  7. How do I trim a file extension from a String in Java?
  8. how to compile & run java program in another java program?
  9. Run Java class file from PHP script on a website
  10. How to set working directory with ProcessBuilder
  11. Why does ‘java -version’ go to stderr?
  12. Continuously read from STDOUT of external process in Ruby
  13. Writing to InputStream of a Java Process
  14. How can I cause a child process to exit when the parent does?
  15. How to add a timeout value when using Java’s Runtime.exec()?
  16. Java native process timeout
  17. Redirection with Runtime.getRuntime().exec() doesn’t work
  18. launch an exe/process with stdin stdout and stderr?
  19. Launch JVM process from a Java application use Runtime.exec?
  20. Is there one JVM per Java application?
  21. CreateProcess error=2, The system cannot find the file specified
  22. java.util.scanner throws NoSuchElementException when application is started with gradle run
  23. Wait for process to finish before proceeding in Java
  24. Launch Firefox and Wait until it is Closed
  25. How do I find the process ID (pid) of a process started in java? [duplicate]
  26. Capturing contents of standard output in Java
  27. Having spaces in Runtime.getRuntime().exec with 2 executables
  28. Why do System.err statements get printed first sometimes?
  29. Runtime.getRuntime().exec(cmd) hanging
  30. What’s the fastest way to read from System.in in Java?

Leave a Comment