Java: How to make this main thread wait for the new thread to terminate
- by Jeff Bullard
I have a java class that creates a process, called child, using ProcessBuilder. The child process generates a lot of output that I am draining on a separate thread to keep the main thread from getting blocked. However, a little later on I need to wait for the output thread to complete/terminate before going on, and I'm not sure how to do that. I think that join() is the usual way to do this but I'm not sure how to do that in this case. Here is the relevant part of the java code.
// Capture output from process called child on a separate thread
final StringBuffer outtext = new StringBuffer("");
new Thread(new Runnable() {
public void run() {
InputStream in = null;
in = child.getInputStream();
try {
if (in != null) {
BufferedReader reader = new BufferedReader(new InputStreamReader(in));
String line = reader.readLine();
while ((line != null)) {
outtext.append(line).append("\n");
ServerFile.appendUserOpTextFile(userName, opname, outfile, line+"\n");
line = reader.readLine();
}
}
} catch (IOException iox) {
throw new RuntimeException(iox);
}
}
}).start();
// Write input to for the child process on this main thread
//
String intext = ServerFile.readUserOpTextFile(userName, opname, infile);
OutputStream out = child.getOutputStream();
try {
out.write(intext.getBytes());
out.close();
} catch (IOException iox) {
throw new RuntimeException(iox);
}
// ***HERE IS WHERE I NEED TO WAIT FOR THE THREAD TO FINISH ***
// Other code goes here that needs to wait for outtext to get all
// of the output from the process
// Then, finally, when all the remaining code is finished, I return
// the contents of outtext
return outtext.toString();
