我没有得到任何输出，可能机器挂起了代码

Question

得到反馈后，我运行该程序，但在控制台中没有任何输出

import java.io.File;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.*;
import java.io.InputStream;

class pbdemo {

    static public void main(String[] args) throws Exception {
        String s;
        ProcessBuilder pb = new ProcessBuilder("cmd.exe", "/f", "dir");
        pb.directory(new File("C:\\ljava"));
        try {
            Process pro = pb.start();
            pro.waitFor();
            BufferedReader br = new BufferedReader(new InputStreamReader(pro.getInputStream()));

            while ((s = br.readLine()) != null) {
                System.out.println("here we go" + s);
            }


        } catch (Exception e) {
            System.out.println("sorry" + e);
        }
    }
}

程序运行，但不输出。

Answer 1

pro.waitFor();是一种阻止方法。它会等到进程退出后再返回。这样做的问题是，许多程序只有在读取/清除标准输出缓冲区后才会退出，这意味着，就您而言，它可能永远不会退出。

尝试这样的事情…

import java.io.File;
import java.io.IOException;
import java.io.InputStream;

public class PBDemo {

    public static void main(String[] args) throws Exception {
        String s;
        ProcessBuilder pb = new ProcessBuilder("cmd.exe", "/c", "dir");
        pb.directory(new File("C:\\ljava"));
        pb.redirectError();
        try {
            Process pro = pb.start();
            InputConsumer ic = new InputConsumer(pro.getInputStream());
            System.out.println("...Waiting");
            int exitCode = pro.waitFor();

            ic.join();

            System.out.println("Process exited with " + exitCode);

        } catch (Exception e) {
            System.out.println("sorry" + e);
        }
    }

    public static class InputConsumer extends Thread {

        private InputStream is;

        public InputConsumer(InputStream is) {
            this.is = is;
            start();
        }

        @Override
        public void run() {
//            This is acutally a bad idea, not all process will write a new line ;)
//            BufferedReader br = new BufferedReader(new InputStreamReader(pro.getInputStream()));

            try {
                int in = -1;
                while ((in = is.read()) != -1) {
                    System.out.print((char) in);
                }
            } catch (IOException exp) {
                exp.printStackTrace();
            }
        }

    }

}