Java UDP多播

Question

我有一个简单的单播客户端/服务器程序与客户端一起工作，询问服务器和服务器应答的内容。 现在我想做一个变体，但添加多播到它。在这个阶段，客户能够加入一个组，并收到确认，如：

hostAddr is /192.168.56.1 and PORT NUMBER IS: 54767 

在服务器端，我从客户期待一个包，但我从来没有得到它。

服务器代码：

import java.io.IOException; 
import java.net.DatagramPacket; 
import java.net.DatagramSocket; 
import java.net.InetAddress; 
import java.net.InetSocketAddress; 
import java.net.MulticastSocket; 
import java.util.HashMap; 

public class MulticastServer 
{ 
public static MulticastSocket socket; 

final static InetSocketAddress d = new InetSocketAddress("239.1.1.3", 4444); 

public static void runNotifier(String m_addr, int m_port) 
{ 
    //final InetSocketAddress d = new InetSocketAddress(m_addr, m_port); 
    (new Thread() 
    { 
     public void run() 
     { 
      while(true) 
      { 
       try { 
        sleep(1000); 
       } catch (InterruptedException e) { 
        e.printStackTrace(); 
       } 
       byte[] hello = ("hello").getBytes(); 
       DatagramPacket h = new DatagramPacket(hello, hello.length, d.getAddress(), d.getPort()); 
       //System.out.println("ADDR: " + d.getAddress() + " PORT: " + d.getPort()); 
       try { 
        //System.out.println("SENDING"); 
        socket.send(h); 
       } catch (IOException e) { 
        e.printStackTrace(); 
       } 
      } 
     } 
    } 
    ).start(); 

} 

public static void initSocket(int port) throws IOException 
{ 
    socket = new MulticastSocket(); //port 
    socket.setTimeToLive(1); 
} 

public static void main(String args[]) throws Exception 
{ 
    initSocket(4444); 
    runNotifier("239.1.1.3", 4444); 
    HashMap<String, String> cache = new HashMap<String, String>(); 
    DatagramSocket serverSocket = new DatagramSocket(4444); 

    byte[] receiveData = new byte[1024]; //buffers   
    byte[] sendData = new byte[1024]; 
    System.out.println("BEFORE SERVER WHILE"); 
    while(true) 
    { 
     System.out.println("INSIDE SERVER WHILE"); 
     DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);     
     serverSocket.receive(receivePacket); 
     System.out.println("RECEIVED FROM CLIENT"); 
     //recebe string do cliente 
     String sentence = new String(receivePacket.getData(),0, receivePacket.getLength()); 
     /* 
     String[] parts = sentence.split(" "); 

     if (sentence.contains(" ")) {      
      cache.put(parts[1], parts[2]); 
     } else { 
      System.out.println("SERVER can't do anything with this."); 
     } 

     //String name = cache.get(parts[1]); 
     */ 
     System.out.println("CLIENT SAID: " + sentence); 
     //System.out.println("THE NAME IS: " + name); 

     InetAddress IPAddress = receivePacket.getAddress();     
     int port = receivePacket.getPort();     
     String capitalizedSentence = sentence.toUpperCase();     
     sendData = capitalizedSentence.getBytes();     
     DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, IPAddress, port);     
     serverSocket.send(sendPacket); 
     receiveData = null; 
     } 
} 
} 

客户端代码

import java.io.*; 
import java.net.*; 
import java.util.*; 

public class MulticastClient { 

public static MulticastSocket socket = null; 

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

    socket = new MulticastSocket(4444); //multicast port 
    InetAddress address = InetAddress.getByName("239.1.1.3"); //multicast address 
    socket.joinGroup(address); 
    System.out.println("JOINED GROUP"); 
    //recebe o hello 
    byte[] a = new byte[1024]; 
    DatagramPacket p = new DatagramPacket(a, a.length); 
    socket.receive(p); 
    System.out.println("RECEIVED PACKAGE"); 
    InetAddress hostAddr = p.getAddress(); 
    int portNumber = p.getPort(); 
    System.out.println("hostAddr is " + hostAddr + " and PORT NUMBER IS: " + portNumber); 
    // 

    HashMap<String, String> cache = new HashMap<String, String>(); 
    //DatagramSocket serverSocket = new DatagramSocket(p.getPort());    

    byte[] receiveData = new byte[1024]; //buffers   
    byte[] sendData = new byte[1024];  

    /* DatagramPacket packet; 
    byte[] buf = new byte[256]; 
    packet = new DatagramPacket(buf, buf.length); 
    socket.receive(packet);*/ 

    //escrita consola 
    BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in)); 
    String sentence = inFromUser.readLine();  
    sendData = sentence.getBytes(); 

    DatagramSocket clientSocket = new DatagramSocket();  

    DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, hostAddr, portNumber);  
    clientSocket.send(sendPacket);  
    System.out.println("SENT TO SERVER"); 
    DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);  
    clientSocket.receive(receivePacket);  

    String modifiedSentence = new String(receivePacket.getData());  
    System.out.println("SERVER: " + modifiedSentence);  
    clientSocket.close();   

socket.leaveGroup(address); 
socket.close(); 
} 

} 

我最好的猜测到目前为止，在服务器53线

DatagramSocket serverSocket = new DatagramSocket(4444); 

我使用的是不正确的端口数。如果客户端收到端口54767，则它将发送到该端口。但即使假设是这个问题，我也不知道如何解决它，因为每次运行它时，客户端都会得到不同的端口。

另一个问题我是，我似乎无法运行两个客户同时由于错误

Exception in thread "main" java.net.SocketException: Unrecognized Windows Sockets error: 0: Cannot bind 

在客户端线12

socket = new MulticastSocket(4444); //multicast port 

预先感谢您的时间。

Answer 1

1-您可以在服务器端创建一个MulticastSocket来接收消息。
2-我认为你不需要DatagramSocket与gorup中的其他人进行通信，MulticastSocket可以很好地作为客户端和服务器。第12行的绑定错误只是为了它。