java Runtime class help needed

ludeKing · 09-20-2004, 06:03 AM

Hi all,
I have read a bit about how people use the Runtime class improperly... and I'm now one of them!

Basically, I need to run a few Linux system commands, such as "gzip" and "tar" from within Linux, but I'm not getting any result at all.

here's my code:

Code:

        String expand = "tar -xzvf " + file_to_expand; //where expand the full path to a filename
        System.out.println(expand);
        
        
        Runtime r = Runtime.getRuntime();
        Process p = null;
        try {
            p = r.exec(expand);
            System.out.println("Opening");
        }
        catch (Exception e) {
            System.out.println("Error, argh");
        }

This gives me:

Code:

tar -xzvf /home/stevo/Desktop/sources/misc.tar
Opening

but nothing. Its getting inside the try block, but not doing much... ie the tar archive isn't expnded. Is there something I missed? I read something about catching the output, but how can I do this?

Cheers.

ToniT · 09-20-2004, 05:23 PM

You don't wait for the process to finish, nor do you examine the contents of the stdout of the process.

foo_bar_foo · 09-20-2004, 10:20 PM

let's see
you shouldn't have to catch the expanding archive
you can catch stdout and stderr though
this should catch the errors if there are any
(might help)
also might help not to get the runtime early but i don't know
wonder how many mistakes i made

Code:

        
        String expand = "tar -xzvf " + file_to_expand; //where expand the full path to a filename
        System.out.println(expand);
        Process p;
        InputStream is;
        BufferedReader br;
        try {
            p = Runtime.getRuntime().exec(expand);
            System.out.println("Opening");
            // i thing stdout is getOutputStream();
            is = p.getErrorStream();
            br = new BufferedReader(new InputStreamReaded(is));
            int c;
            boolean what = true;
            while (what) {
                c = br.read();
                 if (c==-1) {
                     what = false;
                 }
                 System.out.print((char)c);
             }
             is.close();
             br.close();
        }
        catch (Exception e) {
            System.out.println("Error, argh");
        }

paulsm4 · 09-20-2004, 11:29 PM

Hi -

Your program should in fact be doing exactly what you asked it to: extract the specified archive:

1. Here's my version of your code:

Code:

import java.*;

public class DoExec {

  static final String expand = "tar xvf /tmp/tmp.tar";

  public static void main (String[] args) {
    System.out.println(expand);

    Runtime r = Runtime.getRuntime();
    Process p = null;
    try {
      p = r.exec(expand);
      System.out.println("Opening");
    }
    catch (Exception e) {
      System.out.println("Error, argh: " + e.getMessage ());
    }
  }

}

2. Here's the output I got (same as the output you got - basically, nothing. Because you're not trapping stdout. And, of course, you don't *need* to if you don't want to.):

Code:

/tmp/temp> java DoExec
tar xvf /tmp/tmp.tar
Opening

3. And finally, here are the files I extracted from running "DoExec":

Code:

rw-r--r--  1 paulsm users 929 2004-09-20 21:24 DoExec.class
-rw-r--r--  1 paulsm users   1 2004-09-20 21:18 file.1.txt
-rw-r--r--  1 paulsm users   1 2004-09-20 21:18 file.2.txt
-rw-r--r--  1 paulsm users   1 2004-09-20 21:18 file.3.txt

ludeKing · 09-21-2004, 05:31 AM

Damn, how come mine isn't working?
Could it be the string I am passing? (expand) ?

Hang on, I just typed the expand string into the console:

Code:

stevo@h4x0r:~$ /bin/tar -xvf /home/stevo/Desktop/sources/misc.tar
i live at home in a trailer.txt
linux behind magic of shrek2.html
my geek code.txt

BUT, the tar file is STILL NOT EXPANDED! Looks as though its just looking inside the file, but not expanding it.
I then omit the "/bin/" and it still doesn't work. Same output, but no result! Am I missing something completely obvious?