使用非阻塞I / O从Runtime（）。exec读取输入

Question

It seems that using BufferedReader to read a process's InputStream will somehow result in a block I/O behavior. And the effect is like the program doesn't get the instant input from the process. I know there are more lines that could be read at that time, but the BufferedReader just keep waiting for sometime then I can finally get the lines updated.

Here is the code:

While((str=bufferedReader.readLine()!=null) {
  System.out.println(str);
}

Is there some kinds of method that can keep reading from the process without blocking in the while() condition? cause the process won't return null or anything....

Answer 1

You can read the child process output in a separate thread. Something like this

static BlockingQueue<String> queue = new LinkedBlockingDeque<>();

public static void main(String[] args) throws Exception {
    Process p = Runtime.getRuntime().exec("cmd /c dir");
    final BufferedReader rdr = new BufferedReader(new InputStreamReader(p.getInputStream()));
    Thread t = new Thread() {
        public void run() {
            try {
                for (String line; (line = rdr.readLine()) != null;) {
                    queue.put(line);
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    };
    t.start();
    for (;;) {
        String line = queue.poll();
        if (line != null) {
            System.out.println(line);
        } else if (!t.isAlive()) {
            break;
        }
    }
}

Answer 2

You can use the NuProcess library for non-blocking I/O to external processes. Consider it a replacement for ProcessBuilder and Process in Java.