多线程Java Publisher服务器聊天程序

Question

我正在尝试创建一个聊天应用程序，它有一个发布者、一个服务器和多个订阅者。发布服务器（发送到端口8000）向服务器（监听端口8000和5000）发送消息，服务器将消息转发给订阅者（监听端口5000）

现在到目前为止，我可以创建多个发布服务器，服务器和发布服务器之间的通信正常，但是，我无法将发布服务器发送的消息发送给订阅服务器

服务器端代码

package serverclient;
import java.io.*;
import java.net.*;
import java.util.logging.Level;
import java.util.logging.Logger;
public class Server extends Thread{
private Socket socket;
private int clientNumber;

public Server(Socket socket, int clientNumber){
    this.socket  = socket;
    this.clientNumber = clientNumber;
    if(socket.getLocalPort() == 5000)System.out.print("\nSubscriber "+ clientNumber +" is connected to the server");
    if(socket.getLocalPort() == 8000)System.out.print("\nPublisher "+ clientNumber +" is connected to the server");
} 

@Override
public void run(){
    try {
        BufferedReader dStream = new BufferedReader(new InputStreamReader(socket.getInputStream()));
        PrintWriter out = new PrintWriter(socket.getOutputStream(), true);

        while(true){
            synchronized(this){
                String clMessage = dStream.readLine();
                System.out.println("\n"+clMessage);
                // if(socket.getLocalPort() == 5000){
                    out.println("Hey the server is sending the message to subscriber");
                // }    
                //out.println("Hey the publisher has sent the message :  " + clMessage);
            }
        }

    } catch (IOException ex) {
        System.out.print("\nError has been handled 1\n");
    }finally{
        try {
            socket.close();
        } catch (IOException ex) {
            System.out.print("\nError has been handled 2\n");
        }
    }

}

public static void main(String [] args) throws IOException{
    int subNumber = 0;
    int pubNumber = 0;
    ServerSocket servSockpub = new ServerSocket(8000);   
    ServerSocket servSocksub = new ServerSocket(5000);
    try {
        while (true) {
            Server servpub = new Server(servSockpub.accept(),++pubNumber);
            servpub.start();
            System.out.print("\nThe server is running on listen port "+ servSockpub.getLocalPort());
            Server servsub = new Server(servSocksub.accept(),++subNumber);
            servsub.start();
            System.out.print("\nThe server is running on listen port "+ servSocksub.getLocalPort());
        }
    } finally {
        servSockpub.close();
        servSocksub.close();
    }
}

 }

出版商代码

 package serverclient;
 import java.net.*;
 import java.io.*;

公共类出版商{ 公共静态void main（字符串[]args）引发IOException{

    Socket sock = new Socket("127.0.0.1",8000);

    // reading from keyboard (keyRead object)
    BufferedReader keyRead = new BufferedReader(new InputStreamReader(System.in));

    // sending to client (pwrite object)
    OutputStream ostream = sock.getOutputStream(); 
    PrintWriter pwrite = new PrintWriter(ostream, true);

    InputStream istream = sock.getInputStream();
    BufferedReader receiveRead = new BufferedReader(new InputStreamReader(istream));

    System.out.println("Start the chitchat, type and press Enter key");

    String receiveMessage,sendMessage;               
    while(true)
    {
        sendMessage = keyRead.readLine();  // keyboard reading
        pwrite.println(sendMessage);       // sending to server
        pwrite.flush();                    // flush the data  

        if((receiveMessage = receiveRead.readLine()) != null) //receive from server
        {
            System.out.println(receiveMessage); // displaying at DOS prompt
        }  
        else{
            System.out.print("Null");
        }
    }

}
   }

订户

    package serverclient;

    import java.io.BufferedReader;
    import java.io.IOException;
    import java.io.InputStream;
    import java.io.InputStreamReader;
    import java.io.OutputStream;
    import java.io.PrintWriter;
    import java.net.Socket;


   public class Subscriber {
    public static void main (String [] args) throws IOException{

    Socket sock = new Socket("127.0.0.1",5000);

  // receiving from server ( receiveRead  object)
    InputStream istream = sock.getInputStream();
    BufferedReader receiveRead = new BufferedReader(new InputStreamReader(istream));

    System.out.println("Recive side");

    String receiveMessage, sendMessage;  
    while(true)
    {
        System.out.print("Hey man " + receiveRead.readLine() + "\n");
        if((receiveMessage = receiveRead.readLine()) != null) //receive from server
        {
            System.out.println(receiveMessage); // displaying at DOS prompt
        }  
        else{
            System.out.print("Null");
        }
    }

}

}

感谢您的帮助。我只是想弄清楚订户为什么没有收到消息

Answer 1

处理领域时间通信问题有很多可能性。我自己更喜欢使用Events/EventListeners
目前在您的程序中，服务器本身与处理订户连接的线程之间没有通信

还有一个侧节点：即使发布者连接线程和订阅者连接线程之间进行了正确的通信，它现在也无法工作，因为您使用的是相同的Server类。这不仅违反了Single-Responsibility-Principle规则，而且还会阻止服务器向订阅者发送消息

假设您已经建立了连接，并且您的服务器类现在已与订阅者连接。会发生什么
订户将循环，直到其套接字的输入流上出现消息。很好，这正是我们想要的。但是服务器做什么呢？事实是完全一样的。服务器的run方法的try块中的前几条语句是创建一个BufferedReader并从中读取，直到收到消息为止。现在，我们在每个站点上都有一个套接字，它将无限期地等待某种消息的到来（这显然永远不会发生，因为两个都在等待某样东西）

为了防止出现这种情况，您应该先检查流中是否有任何内容需要读取：

while ( true )
{
    if ( socket.getInputStream().available() != 0 )
    {
      // reading logic goes here.... 
      synchronized ( this )
      {
            String clMessage = dStream.readLine();
            System.out.println( "\n" + clMessage );
            out.println( "Hey the server is sending the message to subscriber" );
       }
     }
     // what shall be done when not reading.
}

---

现在是第二部分。如果想要在线程之间通信，需要实现一些逻辑。如上所述，我喜欢听众的概念，因此我将展示一个示例，其中我使用了他们：

MessageReceivedListener。java

import java.util.EventListener;

public interface MessageReceivedListener
    extends EventListener
{

  public void onMessageReceived( String message );

}

注意：接口不必扩展EventListener，因为EventListener 只是一个标签界面。我自己仍然更喜欢用它来提醒界面的用途

服务器。java（节选）

// New constructor since we will pass a Listener now. Also new local variable for it.
public Server( Socket socket, int clientNumber, MessageReceivedListener mrl )
  {
    this.socket = socket;
    this.clientNumber = clientNumber;
    this.mrl = mrl;
    if ( socket.getLocalPort() == 5000 )
      System.out.print( "\nSubscriber " + clientNumber + " is connected to the server" );
    if ( socket.getLocalPort() == 8000 )
      System.out.print( "\nPublisher " + clientNumber + " is connected to the server" );
  }

新的构造函数提供了一种将MessageReceivedListener传递给服务器对象的方法。或者你也可以为它创建一个setter

synchronized ( this )
      {
        String clMessage = dStream.readLine();
        System.out.println( "\n" + clMessage );
        out.println( "Hey the server is sending the message to subscriber" );
        mrl.onMessageReceived( clMessage );
      }

这就是魔法发生的地方。收到消息后，我们只需将其传递给侦听器的onMessageReceived(String message)方法。但它到底有什么作用呢？这是我们在创建服务器对象时定义的。 这里有两个例子，一个是匿名类（Java7和更早版本），另一个是lambdas（Java8和更高版本）

示例Java 7及更早版本

Server servpub = new Server( servSockpub.accept(), ++pubNumber,
            new MessageReceivedListener()
            {

              @Override
              public void onMessageReceived( String message )
              {
                // call nother local method
                // this method would need to be a static method of Server
                // because it's in the scope of your server class
                sendMessageToSubscribers(message);
              }
            } );

在这里，我们传递一个anonymous class作为MessageReceivedListener对象，并定义它的行为（在本例中，只调用另一个将处理其余部分的方法）

---

现在，由于我们的MessageReceivedListener接口只包含一种方法，我们也可以将其视为功能接口，因此使用lambdas来缩短代码并提高可读性

Lambda（Java 8及更高版本）示例

Server servpub = new Server( servSockpub.accept(), ++pubNumber, Server::sendMessageToSubscribers);

在这个特定的例子中，我们只有一个参数要传递给一个方法，因此可以使用method reference

如何真正实现方法sendMessageToSubs(String message)取决于您。但是，您需要跟踪创建了多少具有订户连接的线程，以及希望如何引用它们