Java exec method, how to handle streams correctly

Question

What is the proper way to produce and consume the streams (IO) of external process from Java? As far as I know, java end input streams (process output) should be consumed in

Answer 1

waitFor signals that the process ended, but you cannot be sure the threads which collect strings from its stdout and stderr finished also, so using a latch is a step in the right direction, but not an optimal one. Instead of waiting for the latch, you can wait for the threads directly:

Thread stdoutThread = new Thread(new StreamConsumer(procOut, output)).start();
Thread stderrThread = ...
...
int ret = exec.waitFor();
stdoutThread.join();
stderrThread.join();

BTW, storing lines in StringBuffers is useless work. Use ArrayList instead, put lines there without any conversion, and finally retrieve them in a loop.