Windows process exec'ed from Java not terminating

Question

I'm creating a process on Windows from Java. My problem is that this process doesn't terminate. Here's a sample program:

import java.io.IOException;

public class Test {

/**
 * @param args
 * @throws IOException
 * @throws InterruptedException
 */
public static void main(String[] args) throws IOException,
        InterruptedException {
    Process process = Runtime.getRuntime().exec("cmd /c dir");
    process.waitFor();
    }
}

For reasons beyond my understanding, this program never completes. This is true if "cmd /c dir" is replaced with ipconfig as well as other things.

I can see using ProcessExplorer that java creates the cmd process. This sample is obviously a simplification; in my original program I found that if I call process.destroy() after a while and check the cmd process output, the command is executed successfully.

I've tried this with various releases of Java 1.5 and 1.6. My OS is Windows XP Pro, SP 2.

Answer 1

Likely that you just need to read the stdout and stderr of the process, or it will hang since its output buffer is full. This is easiest if you redirect stderr to stdout, just to be safe:

public static void main(String[] args) throws IOException,
                InterruptedException {
        String[] cmd = new String[] { "cmd.exe", "/C", "dir", "2>&1" };
        Process process = Runtime.getRuntime().exec(cmd);
        InputStream stdout = process.getInputStream();
        while( stdout.read() >= 0 ) { ; }
        process.waitFor();
    }
}

Answer 2

See this link for an explanation.

You need to read the input stream. Also the java process doesn't work like a dos shell. You need to pass the arguments yourself:

String[] cmd = new String[3];
cmd[0] = "cmd.exe" ;
cmd[1] = "/C" ;
cmd[2] = "dir";
Runtime rt = Runtime.getRuntime();
Process proc = rt.exec(cmd);