java - Process 类的 getOutputStream 方法如何工作？

Question

我正在研究 ProcessBuilder class ，其中表示每个流程构建器管理的流程属性之一如下:

a source of standard input. By default, the subprocess reads input from a pipe. Java code can access this pipe via the output stream returned by Process.getOutputStream(). However, standard input may be redirected to another source using redirectInput. In this case, Process.getOutputStream() will return a null output stream, for which:

• the write methods always throw IOException
• the close method does nothing

然后我查找了名为 getOutputStream 的 API 函数，但是它仍然没有点击 m。

我不明白他们这句话的意思:

Output to the stream is piped into the standard input of the process represented by this Process object.

只是寻找有关其工作原理的说明或可能的示例代码。谢谢

Answer 1

这是一个简单的示例代码。

public class ParentProcess {

    public static void main(String[] arags) throws IOException, InterruptedException {
        Process p = new ProcessBuilder(
            "java", "-cp", "bin", "stackoverflow.ChildProcess").start();
        // receive from child
        new Thread(() -> {
            try {
                int c;
                while ((c = p.getInputStream().read()) != -1)
                    System.out.write((byte)c);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }).start();
        // send to child
        try (Writer w = new OutputStreamWriter(p.getOutputStream(), "UTF-8")) {
            w.write("send to child\n");
        }
        System.out.println("rc=" + p.waitFor());
    }

}

class ChildProcess {

    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        // receive from parent and send to parent
        System.out.println("child recevied: " + s.nextLine());
    }

}

结果是:

child recevied: send to child
rc=0