ProcessBuilder: Forwarding stdout and stderr of started processes without blocking the main thread

Question

I'm building a process in Java using ProcessBuilder as follows:

ProcessBuilder pb = new ProcessBuilder()         .command("somecommand", "arg1", "arg2")         .redirectErrorStream(true); Process p = pb.start();  InputStream stdOut = p.getInputStream(); 

Now my problem is the following: I would like to capture whatever is going through stdout and/or stderr of that process and redirect it to System.out asynchronously. I want the process and its output redirection to run in the background. So far, the only way I've found to do this is to manually spawn a new thread that will continuously read from stdOut and then call the appropriate write() method of System.out.

new Thread(new Runnable(){     public void run(){         byte[] buffer = new byte[8192];         int len = -1;         while((len = stdOut.read(buffer)) > 0){             System.out.write(buffer, 0, len);         }     } }).start(); 

While that approach kind of works, it feels a bit dirty. And on top of that, it gives me one more thread to manage and terminate correctly. Is there any better way to do this?

Answer 1

Use ProcessBuilder.inheritIO, it sets the source and destination for subprocess standard I/O to be the same as those of the current Java process.

Process p = new ProcessBuilder().inheritIO().command("command1").start(); 

If Java 7 is not an option

public static void main(String[] args) throws Exception {     Process p = Runtime.getRuntime().exec("cmd /c dir");     inheritIO(p.getInputStream(), System.out);     inheritIO(p.getErrorStream(), System.err);  }  private static void inheritIO(final InputStream src, final PrintStream dest) {     new Thread(new Runnable() {         public void run() {             Scanner sc = new Scanner(src);             while (sc.hasNextLine()) {                 dest.println(sc.nextLine());             }         }     }).start(); } 

Threads will die automatically when subprocess finishes, because src will EOF.