java - 读取守护进程的输入流导致程序卡住

Question

出于测试目的，我需要从命令行启动守护进程，并且需要读取该进程的输出(输入流、错误流)。当我尝试读取进程输出时，它卡在 bufferedReader.readLine()

    String command = "start server";
    String output = "";
    ProcessBuilder pb = new ProcessBuilder("cmd.exe", "/c");
    pb.directory(new File("C:\\tmp"));
    Process proc = null;
    try {
        proc = pb.start();
        BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(proc.getOutputStream()));
        writer.write(command, 0, command.length());
        writer.newLine();
        writer.close();
        proc.waitFor(20, TimeUnit.SECONDS);
        BufferedReader stdInput = new BufferedReader(new InputStreamReader(proc.getInputStream()));
        BufferedReader stdError = new BufferedReader(new InputStreamReader(proc.getErrorStream()));
        String line;
        while ((line = stdInput.readLine()) != null) {
            output = output + line + "\n";
            System.out.println(output);
        }
        while ((line = stdError.readLine()) != null)
            output = output + line + "\n";
        ByteArrayOutputStream opStream = new ByteArrayOutputStream();
        opStream.writeTo(proc.getOutputStream());
        String stdOutput = new String(opStream.toByteArray());
        output = output + stdOutput;
    } catch (Exception e) {
        System.out.println("Exception while running command. " + e.getMessage());
    } finally {
        if (proc != null)
            proc.destroyForcibly();
        System.out.println(output);
    }

我可以对缓冲读取器使用超时，以便程序不会卡住。调用守护进程并读取其输出的最佳方法是什么？

Answer 1

标准 java io 是阻塞的。您可能可以使用 new io (nio)，但它还有其他缺点(使用起来很复杂)。

如果你想使用java io，一种方法是从两个单独的线程读取两个流。 (您需要分别排出两个流，因为每个流都有一个固定大小的缓冲区。如果其中一个缓冲区填满，整个过程就会卡住，直到它被排出)

类似于:

private static class StreamGobbler implements Runnable {
    private final InputStream stream;

    private final ByteArrayOutputStream output;

    public StreamGobbler(InputStream stream) {
        this.stream = stream;
        output = new ByteArrayOutputStream();
    }

    @Override
    public void run() {
        try {
            int read;
            while ((read = stream.read()) >= 0) {
                output.write(read);
            }
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

{
    StreamGobbler stdin = new StreamGobbler(proc.getInputStream());
    StreamGobbler stdout = new StreamGobbler(proc.getErrorStream());
    Executor executor = Exectors.newFixedThreadPool(2);
    executor.submit(stdin);
    executor.submit(stdout);

    // do io for process
    // wait for process to finish
    // shutdown executorservice

    byte[] stdinBytes = stdin.output.toByteArray();
    byte[] stderrBytes = stderr.output.toByteArray();

}