Allow Java to end with main() without closing processes that were exec()uted

Question

I am launching a process with Runtime.getRuntime().exec()

However, once Java reaches the end of the main() loop, java will not close, unless I destroy() the process first.

Problem with that is, I need the process to keep running after Java is closed.

I pretty much want to do this

public static void main(String args[]) {
  Runtime.getRuntime().exec("file.bat");
  // now I want java to close, and I want file.bat to keep running
}

I tried System.exit(), it will stop my main() loop, however I think a thread or something that was started by exec() keeps running, preventing java from closing. I can't even end it in Eclipse without first exiting file.bat

Why isn't it closing? And how would I fix it?

I couldn't find anything online, and I've been experimenting for a while, so I decided to ask you guys.

Thank you, -Alex Benoit

Answer 1

Figured it out. I'll share my code in case anyone else has the same question. I brought it down to 1 line.

Desktop.getDesktop().open(new File("C:\\Folder\\File"));

Answer 2

Launch the file with cmd for Windows Only

Older windows will probably have to use command.com instead

Runtime.getRuntime().exec("cmd /c start file.bat");

Using the start with /wait parameter waits until bat is finished without /wait it should work.

public class Command {

public static void main(String[] args) throws java.io.IOException, InterruptedException {
       String path = "C:\\DOCUME~1\\\USER\\DESKTOP";

       Process p = Runtime.getRuntime().exec("cmd /c start /wait " + path + "\\test.bat");

       System.out.println("Waiting for batch file ...");
       p.waitFor();
       System.out.println("Batch file done.");
   }
}

test.bat

@echo off
cls
:start
echo This is a loop
goto start

Use the command.com file to get short path name, since long path names don't get processed too well in start program.

Here is a sample I made download link below: https://www.mediafire.com/?mu7vht3e6tto698

Your problem may be that you are not on a Windows Administrator account you could try, But this requires you to type in your Administrator password which is very stupid.

Process p = Runtime.getRuntime().exec("runas /profile /user:Administrator \"cmd.exe /c start test.bat\"");

Answer 3

This is a system dependent question. I am not sure if in Windows the parent process can terminate before the child. I believe this is true in linux.

As a guideline, you should call waitFor() on the process. However, on some systems, just doing so might not be enough. As pointed out in the javadoc, the out/err stream need to be properly purged (using the streams returned by getOutputStream() and getErrorStream()) because they could keep your process from completing. To do so, I found it most appropriate to use two separate threads, one purging the err stream, the other the out stream. The calling thread (main in your case), has to do the following:

• start the external process;
• start a thread to purge the out stream;
• start a thread to purge the err stream;
• call waitFor() on the calling thread (main).

I found the above approach very robust and easy to implement (if you are familiar with threads). Please use an ExecutorService for the threads.