Process.waitFor() causes program to hang!

Question

I've successfully created a Process and run it using Runtime's exec(String path), and the kinds of processes I've successfully run have included Winzip, a WS_FTP Pro script, and a regular .bat file. I've also successfully called waitFor() on these processes, but in this particular case I'm calling a program that takes a file I give it as a parameter and merges its data into a database. I've been doing this procedure for a while (either from a command line or in a .bat file), but now I need to call it from my Java code. Preferably I'd like to waitFor() the process each time because I need to make sure all the files are merged in chronological order. My current test case only uses ONE file, but in reality there will be several. With one file, I can run the program and it appears to run fine (and it runs fast--like maybe a second or two at most), but whenever I call the following line it hangs indefinitely (I've never seen it terminate, even after several minutes):
focusProcess.waitFor();
When I just execute that program by itself by calling a .bat file with a hardcoded filename, I get standard output back from the program I'm calling. I'd like to see this output when I run my Java program and it appears to run fine, because I have no way if it IS running correctly! So, I added the following:
BufferedInputStream bis = new BufferedInputStream(focusProcess.getInputStream());
StringBuffer sb = new StringBuffer();
int c;
while((c=bis.read()) != -1) {   
sb.append(c);
bis.close();
I'm not sure if this is the right way to monitor that InputStream that I get from the process, and even if that InputStream is going to give me the standard output from that the process normally writes to the terminal. All I do know is that again, the program seems to hang indefinitely, and I guess it has to do with the fact that maybe this process isn't notifying me that it's terminated, and so I'm still waiting for the rest of that InputStream. And yes, I HAVE tried both of these situations together AND separately (so I know that both pieces of code cause the program to hang).
Any ideas would be much appreciated!

Answer 1

Paying attention to the standard output from the running process is good for debugging (and reporting program progression, if necessary) but probably doesn't contribute to the problem you are seeing. The standard input to the process, however, is a different story. If the process you have Runtime.exec'd is waiting for something on stdin, then the OS will block on behalf of the program that is blocking for input and never terminate!
Try running the exec'd command from the command-line and see if it needs any input (i.e. you have to press a key, or enter, or send EOF) for the program to complete. If this is the case then your Java program must supply that process with the appropriate input or it will just hang.
As for printing the output from a process... here's a quick proof of concept:
import java.io.*;
public class Exec {
    public static void main(String args[]) throws Exception {
        // Make sure we've got something to exec.
        if ( args == null || args.length < 1 ) {
            System.out.println("Usage: java Exec COMMAND [ARGS...]");
            System.exit(1);
        // Run the process and print the output.
        Process p = Runtime.getRuntime().exec(args);
        BufferedReader in = new BufferedReader(new InputStreamReader(p.getInputStream()));
        String line;
        while ( (line=in.readLine()) != null ) {
            System.out.println("EXEC: "+line);
}Hope this helps!
-mike