Re: Runtime.exec(cmd) hangs up

From:

Vic <vikrantp@gmail.com>

Newsgroups:

comp.lang.java.programmer

Date:

25 May 2007 12:43:10 -0700

Message-ID:

<1180122190.487170.204980@a35g2000prd.googlegroups.com>

Alright so here is my new code now, I implemented it the way you said
(with some online help)
class StreamGobbler extends Thread {
    InputStream is;
    String type;

    StreamGobbler(InputStream is, String type){
        this.is = is;
        this.type = type;
    }

    public void run(){
        try{
            InputStreamReader isr = new InputStreamReader(is);
            BufferedReader br = new BufferedReader(isr);
            String line = null;
            while((line = br.readLine()) != null){
                System.out.println(type+">"+line);
            }
        }
        catch(IOException ioe){
            ioe.printStackTrace();
        }
    }
}

class CommandExecuter {
    public static String stdout = null;
    public static String stderr = null;
    private String line;

    public CommandExecuter (String cmd) throws java.io.IOException{
    System.out.println("CommandExecuter: EXECUTING COMMAND: "+cmd);
    Process proc = Runtime.getRuntime().exec(cmd);

    StreamGobbler errorGobbler = new
StreamGobbler(proc.getErrorStream(),"ERROR");
    StreamGobbler outputGobbler = new
StreamGobbler(proc.getInputStream(),"OUTPUT");

    errorGobbler.start();
    outputGobbler.start();

    try{
        //VicP - temporary code to check the process status
            int val = proc.waitFor();
        //proc.wait(120000);
        }
        catch (Throwable t){
            t.printStackTrace();
        }
}
}
But now the question is how do I set the value of stdout and stderr in
CommandExecuter(As we are doing the stuff in thwo different threads
now)? I need these values as they are checked in the calling function
(which calls the Command executer constructor). Could you please
suggest me some changes to get this?
On May 24, 5:53 pm, "Mike Schilling" <mscottschill...@hotmail.com>
wrote:

"Vic" <vikra...@gmail.com> wrote in message

news:1180046607.237152.145810@r19g2000prf.googlegroups.com...

I am having a problem with Runtime.exec(cmd) where cmd is a string and
is as follows -

cmd = "home/qaplay/loader/604/soaploaderclient.ps nemo 50624 55604
genevaman qa /home/vpatanka/604Current/lib/loader/data/
DuplicateTransactionTest.0.lrd -bcp > & $GVHOME/tempOut.txt"

The actual code is like this ->
public CommandExecuter (String cmd) throws java.io.IOException{
   System.out.println("CommandExecuter: EXECUTING COMMAND: "+cmd);
   Process proc = Runtime.getRuntime().exec(cmd);

   BufferedReader in = new BufferedReader(new
InputStreamReader(proc.getInputStream()));
   BufferedReader err = new BufferedReader(new
InputStreamReader(proc.getErrorStream()));

stdout = "";
while ((line = in.readLine()) != null)
    stdout += line +"\n";
if (stdout == "")
    stdout = null;

stderr = "";
while ((line = err.readLine()) != null)
    stderr += line +"\n";
if (stderr == "")
    stderr = null;

//System.out.println ("CommandExecuter stdout="+stdout);
//System.out.println ("CommandExecuter stderr="+stderr);
   }
}

I can run the same cmd on the shell and I get a an output which is
pretty big so I am not copying it over here but if you guyz need it
then I can do that. Please let me know what am I missing here in
Runtime.exec() or its something else

The obvious issue is that this code won't start to read stderr until the
exec'd process closes stdout, so the process may be hung trying to wite to
stderr. Try reading from stdout and stderr at the same time (in different
threads.) A nice, symmetrical way to do this is

    1. Runtime.exec()
    2. Start a thread that reads from stdout as long as there's anything to
read and then exits.
    3. Start another thread that reads from stderr as long as there's
anything to read and then exits.
    4. Process.waitFor();