在Java中重定向stdin和stdout [英] Redirect stdin and stdout in Java

问题描述

我正在尝试重定向java中的子进程的stdin和stdout，最终我将输出转到JTextArea或其他东西。

I'm trying to redirect stdin and stdout of a subprocess in java, eventually i'm going to have the output go to a JTextArea or something.

这里是我当前的代码，

Process cmd = Runtime.getRuntime().exec("cmd.exe");

cmd.getOutputStream().write("echo Hello World".getBytes());
cmd.getOutputStream().flush();

byte[] buffer = new byte[1024];
cmd.getInputStream().read(buffer);
String s = new String(buffer);

System.out.println(s);

输出如下：

Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation.  All rights reserved.

C:\(Current Directory)>

我期待看到输出的Hello World字符串。
也许是因为父进程没有活得足够长？

I'm expecting to see the "Hello World" string outputted. Maybe because the parent process isn't staying alive long enough?

我也希望能够发送和接收多个命令。

I'd also like to be able to send and receive multiple commands.

推荐答案

在尝试侦听输入流之前，您已尝试写入输出流，因此您有意义一无所获。为了成功，您需要为两个流使用单独的线程。

You've attempted to write to the output stream before you attempt to listen on the input stream, so it makes sense that you're seeing nothing. For this to succeed, you will need to use separate threads for your two streams.

即

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.Scanner;

public class Foo {
   public static void main(String[] args) throws IOException {
      Process cmd = Runtime.getRuntime().exec("cmd.exe");

      final InputStream inStream = cmd.getInputStream();
      new Thread(new Runnable() {
         public void run() {
            InputStreamReader reader = new InputStreamReader(inStream);
            Scanner scan = new Scanner(reader);
            while (scan.hasNextLine()) {
               System.out.println(scan.nextLine());
            }
         }
      }).start();

      OutputStream outStream = cmd.getOutputStream();
      PrintWriter pWriter = new PrintWriter(outStream);
      pWriter.println("echo Hello World");
      pWriter.flush();
      pWriter.close();
   }
}

你真的不应该忽略错误流但是应该吞噬它，因为忽略它有时会炸掉你的过程，因为它可能会耗尽缓冲空间。

And you really shouldn't ignore the error stream either but instead should gobble it, since ignoring it will sometimes fry your process as it may run out of buffer space.

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