在Java中使用IO流

Question

我需要使用Java启动一个二进制文件，然后使用输入流和输出流与其交互。我已经写了一个原型来弄清楚它是如何工作的，但到目前为止，我得到的唯一输出是null。但是，当它自己运行时，子程序会产生输出。我做错了什么？

import java.io.*;

public class Stream {
    public static void main(String args[]) {
    Process SaddleSumExec = null;
    BufferedReader outStream = null;
    BufferedReader inStream = null;

    try {
        SaddleSumExec = Runtime.getRuntime().exec("/home/alex/vendor/program weights.txt list.txt");
    }
    catch(IOException e) {
        System.err.println("Error on inStream.readLine()");
        e.printStackTrace();
    }

    try {
        inStream = new BufferedReader(new InputStreamReader
                      (SaddleSumExec.getInputStream()));
        System.out.println(inStream.readLine());
    }
    catch(IOException e){
        System.out.println("Error.");
    }

    }
}

Answer 1

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;

public class Prompt {
//flag to end readers and writer
boolean processEnd = false;

public static void main(String[] args) {
    new Prompt();
}

public Prompt() {

    Process SaddleSumExec = null;
    Input in = new Input(this);
    Output out = new Output(this);
    Input err = new Input(this);
    //thread to read a write console
    Thread t1 = new Thread(in);
    Thread t2 = new Thread(out);
    Thread t3 = new Thread(err);

    try {
        SaddleSumExec = Runtime
                .getRuntime()
                .exec(
                         "ConsoleApplication1/bin/Debug/ConsoleApplication1");

        in.input = SaddleSumExec.getInputStream();
        err.input = SaddleSumExec.getErrorStream();
        out.out = SaddleSumExec.getOutputStream();
        t2.start();
        t1.start();
        t3.start();

        SaddleSumExec.waitFor();
        processEnd = true;

    } catch (IOException e) {
        System.err.println("Error on inStream.readLine()");
        e.printStackTrace();
    } catch (InterruptedException e) {
        e.printStackTrace();
    }

}

public boolean isProcessEnd() {
    return processEnd;
}

public void setProcessEnd(boolean processEnd) {
    this.processEnd = processEnd;
}
/*Readers of Inputs*/
class Input implements Runnable {
    private BufferedReader inStream;
    InputStream input;
    Prompt parent;

    public Input(Prompt prompt) {
        // TODO Auto-generated constructor stub
        parent = prompt;
    }

    public void run() {
        inStream = new BufferedReader(new InputStreamReader(input));
        while (!parent.isProcessEnd()) {
            try {
                String userInput;
                while ((userInput = inStream.readLine()) != null) {
                    System.out.println(userInput);
                }
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
}
/*Writers of Output*/
class Output implements Runnable {
    OutputStream out;
    Prompt parent;

    public Output(Prompt prompt) {
        parent = prompt;
        // TODO Auto-generated constructor stub
    }

    @Override
    public void run() {

        while (!parent.isProcessEnd()) {
            try {
                String CurLine = "";
                InputStreamReader converter = new InputStreamReader(
                        System.in);
                BufferedReader in = new BufferedReader(converter);

                while (!(CurLine.equals("quit"))) {
                    CurLine = in.readLine();
                    if (!(CurLine.equals("quit"))) {
                        out.write((CurLine + "\n").getBytes());
                        out.flush();
                    }
                }
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
}

}

Answer 2

您似乎并不是在等待子进程结束，所以父进程有可能在有机会读取输出流之前就结束了。

这里有一篇关于Runtime.exec的古老而优秀的文章

http://www.javaworld.com/jw-12-2000/jw-1229-traps.html

正确的实现在这个页面上。

http://www.javaworld.com/jw-12-2000/jw-1229-traps.html?page=4

Answer 3

据我所知，这里可能存在两个问题：

1. 您是否正在尝试在子程序开始读取之前获取对流的访问权限？
2. 您是否正在运行访问权限不足的父进程？