如何在Java中从子线程返回消息到主线程(方法)？

Question

我有一个HashMap，里面的人要互相通信，具体如下。

{zidane=[rooney, rooney, rooney, scholes, rooney], rooney=[scholes, messi, scholes], scholes=[ronaldo], ronaldo=[rooney, messi, scholes], messi=[zidane]}

在这里，每个人都有自己的线程，他们将在其中向他们列表中的每个人发送消息并接收回应。

import java.util.*;

public class Master {
    public Map callsMap = new HashMap<String, List>();

    public static void main(String[] args){
        Master m = new Master();
        m.readFile();
        Iterator<Map.Entry<String, List>> it = m.callsMap.entrySet().iterator();
        while (it.hasNext()) {
            Map.Entry<String, List> pair = it.next();
            String caller = pair.getKey();
            List receiverList = pair.getValue();
            SubTasks st = new SubTasks(caller, receiverList);
            Thread thread = new Thread(st);
            thread.start();
            //st.getMessage();
        }
    }
}

该 master 类将为HashMap中的每个键迭代创建一个线程。请注意 readFile 方法将只是从文本文件中读取并产生输入（进入 callsMap 变量）我在上面已经提到。它对这个上下文不是特别重要，所以我在这里省略了。

我有 SubTasks 类，它扩展了 Thread 类，并为每次交互创建消息。这个类不会创建任何额外的线程，而只是对它收到的调用者和接收者列表进行操作，如下所示。

import java.util.List;

public class SubTasks extends Thread {
    private String caller;
    private List receiverList;
    private volatile String returnMessage;

    SubTasks(String s, List l){
        caller = s;
        receiverList = l;
    }

    public void setMessage(String msg){
        returnMessage = msg;
    }

    public String getMessage() {
        return returnMessage;
    }

    @Override
    public void run(){
        for (int i = 0; i < receiverList.size(); i++) {
            System.out.println(receiverList.get(i)+" received intro message from "+caller +" ["+System.currentTimeMillis()+"]");
            returnMessage = caller+" received reply message from "+receiverList.get(i) +" ["+System.currentTimeMillis()+"]";
            //setMessage(returnMessage);
            System.out.println(returnMessage);
        }
    }
}

如果我在子线程中打印所有26对交互的消息，我得到了想要的输出。

zidane received message from messi [1592117172946]
rooney received message from ronaldo [1592117172946]
scholes received message from rooney [1592117172946]
rooney received message from zidane [1592117172946]
ronaldo received message from scholes [1592117172946]
messi received reply from zidane [1592117172989]
ronaldo received reply from rooney [1592117172989]
...
...

我如何将这些消息传递到主线程（方法）中，并在那里而不是子线程中打印？我试着使用 getter-setter 方法，但是由于线程会随机执行，所以无法调用 getter 方法正确。

Answer 1

我建议你使用 Executor 架构 Callable 界面和 Futures 在你的案例中，因为你需要的所有东西都已经解决了。重写类会帮助你正确解决它。

     public class Master {
        public Map callsMap = new HashMap<String, List>();

            public static void main(String[] args){
                Master m = new Master();
                m.readFile();
                ExecutorService executorService = Executors.newFixedThreadPool(10);// or some desired number
                List<Future<String>> returnFutures = new ArrayList<>();
                Iterator<Map.Entry<String, List>> it = m.callsMap.entrySet().iterator();
                while (it.hasNext()) {
                    Map.Entry<String, List> pair = it.next();
                    String caller = pair.getKey();
                    List receiverList = pair.getValue();
                    returnFutures.add(executorService.submit(new SubTasks(caller, receiverList) ));
                }
                executorService.shutdown();
                while(executorService.awaitTermination(1000, TimeUnit.SECONDS));
                for(Future<String> returnFuture: returnFutures){
                     /* returnFuture.get() will have the returned value from the thread, if the thread has completed execution, 
                     otherwise it will wait for the completion*/
                    System.out.println(returnFuture.get());

                }
            }
    }

和

    public  class SubTasks implements Callable<String> {
        private String caller;
        private List receiverList;
        private volatile String returnMessage;

        SubTasks(String s, List l){
            caller = s;
            receiverList = l;
        }

        public void setMessage(String msg){
            returnMessage = msg;
        }

        public String getMessage() {
            return returnMessage;
        }

        @Override
        public String call (){
            for (int i = 0; i < receiverList.size(); i++) {
                System.out.println(receiverList.get(i)+" received intro message from "+caller +" ["+System.currentTimeMillis()+"]");
                returnMessage = caller+" received reply message from "+receiverList.get(i) +" ["+System.currentTimeMillis()+"]";
                return returnMessage;
            }
        }
    }