Java, system command fails to run.

Question

I'm trying to run a system command to extract a tar.bz2 file to a specified directory. This is the code:

ProcessBuilder myProc = new ProcessBuilder("tar", "-xjf", "/path/to/MyTarFile.tar.bz2"); 
myProc.directory(new File("/directory/i/want/results/in/"));
myProc.start();
System.out.println(myProc.command());

It runs without error, however the file is deleted and not extracted anywhere.

Any help would be greatly appreciated.

Answer 1

Change the myProc.start(); line to

  Process p = myProc.start();
  p.waitFor();

That will make sure your program doesn't exit until the tar is finished.

Answer 2

Run this to see errors. Perhaps one of your paths is incorrect.

import java.io.File;
import java.io.InputStream;

public class Untar {

public static void main(String[] args) throws Exception {
    ProcessBuilder myProc = new ProcessBuilder("tar", "-xjf", "foo.tar.bz2");
    myProc.directory(new File("newdir"));
    Process p = myProc.start();
    InputStream is = p.getErrorStream();
    int c;
    while( (c = is.read()) != -1 ){
       System.out.print((char)c);
    }
    p.waitFor();
    System.out.println(myProc.command());
}

}

Answer 3

I know Runtime.exec() has a really nasty feature where if you don't manually drain STDOUT/STDERR, it effectively appears to hang. I would hope that ProcessBuilder corrected that deficiency, but this page includes this tidbit:

A word of caution about the examples in this tip. It is possible that the examples will deadlock if the subprocess generates enough output to overflow the system. A more robust solution requires draining the process stdout and stderr in separate threads.

So, make sure you're handling Process.getInputStream() and Process.getErrorStream(), as I recommended in the comments; it could solve the problem outright!

Answer 4

Just tried this code. It works.

Check your paths.