BufferedReader readline 如何在连续程序中工作？

Question

So I know I can use readline to get the program output line by line but if I use a while loop

String l;
 while( (l=input.readLine()) != null)
    rcv = rcv + l
 return rcv;

But this freezes my program until the external process finishes giving output. I want to listen to the output as the external process gives it. It can take a long time for the external program to exit.

I tried using read() but it also freezes my program until the end. How can I read the output, whatever is available and then do my processing? and then go back to read output again?

Answer 1

You can use a separate thread to read the input stream. The idea is that the blocking operations should happen in a separate thread, so your application main thread is not blocked.

One way to do that is submitting a Callable task to an executor:

        ExecutorService executor = Executors.newSingleThreadExecutor();
        Future<String> processOutput = executor.submit(() -> {
           // your code to read the stream goes here
           String l, rcv;
           while( (l=input.readLine()) != null) { ... }
           return rcv;
        });

This returns a "future" which is a way to represent a value that may not be available now but might be at some point in the future. You can check if the value is available now, or wait for the value to be present with a timeout, etc.