Wanting to read in stdout before Process Finishes

Question

So, I am running an external script using java Runtime.exec that has a stdout. Now, I feed it into a BufferedReader and read by line, and it works fine. However, this script may hang as its processing, which is not something I can change. However, output should still be coming in, or it does on the terminal. But I can't read the BufferedReader until the Process is complete, then it proceeds to read it all at once.
So, my question is this. Does the Process have to finish before you can read in the stdout in java? If not, how would I go about it?

Answer 1

jking31 wrote:
Here is my java code:
Process pro = Runtime.getRuntime().exec(cmdArr, null, new File(dir));
InputStream stdOut = new InputStream(pro.getInputStream());
InputStream errOut = new InputStream(pro.getErrorStream());
InputStreamReader stdOutReader = new InputStreamReader(stdOut);
InputStreamReader errOutReader = new InputStreamReader(errOut);
BufferedReader stdOutBR = new BufferedReader(stdOutReader);
BufferedReader errOutBR = new BufferedReader(errOutReader);
while ((line = stdOutBR.readLine()) != null) {
System.out.println(line);
while ((line = errOutBR.readLine()) != null) {
System.err.println(line);
}I am fully aware of the fact that this should be threaded to prevent problems, but I am going to be using this to update a JTextArea on a Swing GUI that is not thread safe. Then you should have a Thread for each Stream and update the Swing component with each line using SwingUtilities.invokeLater(). That is what I do and it works great.
My goal in the end is to have stuff print out to the Swing GUI while the process is going, but what ends up happening is that the stdOutBR won't actually be accessible until the Process finished, then it prints it all,If this is being run in the Swing event thread then of course this will happen since you are holding up the Swing event thread until you have read all the data. You should use a Thread and use SwingUtilities.invokeLater() to append each line.
If this is not being run in the Swing event thread then you must make sure that the native program is flushing it's stdout after each line.
but if I were to run this same code on the command line, I get output immediately, telling me what's going on before it starts to hang on a 30 second process.So it sounds like you should use a Thread for each stream and SwingUtilities.invokeLater().