无法通过 Java 运行时进程查看输出

Question

我正在尝试编译然后在 windows 中通过命令行运行程序。

我有以下代码，我尝试了我评论的线程方法，然后尝试了单进程方法。类文件被生成，希望执行也能产生 hello world。如何在字符串中捕获它。请注意，这是我使用的 Windows 机器。

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Scanner;

public class CompilerMain {

  public String doCompile(String compilationLang, String codeString,
                          String challengeName) throws InterruptedException, IOException {

    String output = null;
    String commandString = null;

    if (compilationLang == "java") {

      String path = "c:\\Test\\";

      challengeName = "Solution";
      String commandStringCompile;
      String commandStringExcecute;
      commandStringCompile = "javac " + path + challengeName + ".java";
      commandStringExcecute = "java " + path + challengeName;
      System.out.println("Command is " + commandStringCompile);
      System.out.println("Command is " + commandStringExcecute);
      final Process p = Runtime.getRuntime().exec(commandStringCompile);
      final Process q = Runtime.getRuntime().exec(commandStringExcecute);
      Scanner err = new Scanner(p.getInputStream());
      Scanner in = new Scanner(q.getInputStream());


      while (in.hasNext()) {

        System.out.println(in.next());

      }

      while (err.hasNext()) {

        System.out.println(err.next());

      }

      BufferedReader input = new BufferedReader(
          new InputStreamReader(p.getInputStream()));
      String line = null;

      try {
        while ((line = input.readLine()) != null) {
          System.out.println(line);
        }
      } catch (IOException e) {
        e.printStackTrace();
      }


        /*          
        new Thread(new Runnable() {
            public void run() {

                BufferedReader input = new BufferedReader(
                        new InputStreamReader(p.getInputStream()));
                String line = null;

                try {
                    while ((line = input.readLine()) != null) {
                        System.out.println(line);
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }).start();

        p.waitFor();
        if(p.exitValue()==0){
            System.out.println("Error! Code " + p.exitValue());
            BufferedReader input = new BufferedReader(
                    new InputStreamReader(p.getInputStream()));
            String line = null;

            try {
                while ((line = input.readLine()) != null) {
                    System.out.println(line);
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        if(p.exitValue()!=0){
            BufferedReader input = new BufferedReader(
                    new InputStreamReader(p.getInputStream()));
            String line = null;

            try {
                while ((line = input.readLine()) != null) {
                    System.out.println(line);
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        final Process q = Runtime.getRuntime().exec(commandString);
        commandString = "java "+ challengeName + " >>out.txt";
        new Thread(new Runnable() {
            public void run() {

                BufferedReader input = new BufferedReader(
                        new InputStreamReader(q.getInputStream()));
                String line = null;

                try {
                    while ((line = input.readLine()) != null) {
            //          System.out.println(" 1");

                        System.out.println(line);
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }).start();

        q.waitFor();
        System.out.println("Exit Value is " + q.exitValue());
    */
    }
    return output;
  }
}

Answer 1

您的方法效果很好。可能是您的命令字符串不正确。请尝试从 p.getErrorStream() 和 q.getErrorStream() 中读取，你会看到发生了什么。

我稍微修改了你的代码，以便在我的 Linux 机器上工作。

public String doCompile(String compilationLang, String codeString,
                        String challengeName) throws InterruptedException, IOException {

  String output = null;
  String commandString = null;

  if (compilationLang == "java") {

    String path = "/home/john/IdeaProjects/Test1/src/";

    String commandStringCompile;
    String commandStringExcecute;
    commandStringCompile = "javac " + path + "Main.java";
    commandStringExcecute = "java -cp " + path +" Main";
    System.out.println("Command is " + commandStringCompile);
    System.out.println("Command is " + commandStringExcecute);
    final Process p = Runtime.getRuntime().exec(commandStringCompile);
    final Process   q = Runtime.getRuntime().exec(commandStringExcecute);
    Scanner err = new Scanner(p.getErrorStream());
    Scanner in = new Scanner(p.getInputStream());
    while (in.hasNext()) {
      System.out.println(in.next());
    }
    while (err.hasNext()) {
      System.out.println(err.next());
    }

    err = new Scanner(q.getErrorStream());
    in = new Scanner(q.getInputStream());
    while (in.hasNext()) {
      System.out.println(in.next());
    }
    while (err.hasNext()) {
      System.out.println(err.next());
    }
  }
  return output;
}

输出：

Command is javac /home/john/IdeaProjects/Test1/src/Main.java
Command is java -cp /home/john/IdeaProjects/Test1/src/ Main
hello
world!