Java 多播发送数据，不接收

Posted 2023-03-14

【中文标题】Java 多播发送数据，不接收

【英文标题】：Java Multicast Sending Data, Not Receiving

【发布时间】：2012-01-18 06:36:03

【问题描述】：

我正在用 Java 编写一个类，用于大大简化多播过程。但是，我有两个大问题：

该类发送数据（我可以使用我的网络监视器 Wireshark 验证这一点），但同一组中的任何其他人都没有收到该数据。 在某些机器上，发送数据包的 TTL 在传输过程中超过了（同样，根据 Wireshark）。

谁能帮帮我？几个小时以来，我一直在尝试寻找答案，看来我的代码遵循了连接、加入、发送和接收来自多播主机的数据的所有基本过程。

这是该类相关部分的sn-p：

多播类：

public class Multicaster 
  public int port = 5540;

  protected String IPAddress;

  private MulticastSocket msConn;
  private InetAddress netAddr;

  public Multicaster(String IPAddress) 
    this.IPAddress = IPAddress;
  

  public String recieveData() 
    byte[] buf = new byte[1000];
    DatagramPacket pack = new DatagramPacket(buf, buf.length);

    try 
      this.msConn.receive(pack);
      new Message(pack);
      String out = new String(pack.getData());
      return out.substring(0, pack.getLength());
     catch (IOException e) 
      return new String("");
    
  

  public void joinGroup()  
    try 
      this.msConn.joinGroup(this.netAddr);
     catch (IOException e) 
    //This error shouldn't occur since it would caught by the connect() method during initial connection to the host
    
  

  public void connect() throws MulticasterInitException 
  //Try to create a multicast connection on the given IP address and port
    try 
      try 
      //Create a multicast connection on a given port, throws UnknownHostException
        this.msConn = new MulticastSocket(this.port);

      //If all goes well, then create a connection to a given IP address using the above port number, throws IOException and SecurityException
        this.netAddr = InetAddress.getByName(this.IPAddress);
      
    

  /**
   * Here all of the possible exceptions that are thrown above
   * are caught and handled here. This works just fine.
   */
  

  public void sendData(String data) throws MulticasterSendException 
    DatagramPacket packet = new DatagramPacket(data.getBytes(), data.length(), this.netAddr, this.port);

    try 
      this.msConn.send(packet);
     catch (IOException e) 
      throw new MulticasterSendException("Java could not communicate with the server. Please check your network connections.", e);
    
  

发送数据的示例用法：

Multicaster multicast = new Multicaster("239.0.0.0");

try 
  multicast.connect();
 catch (MulticasterInitException e) 
  //Handle exception...


multicast.joinGroup();

try 
  multicast.sendData("Hi");
 catch (MulticasterSendException e) 
  //Handle exception... 

接收数据的示例用法：

Multicaster multicast = new Multicaster("239.0.0.0");

try 
  multicast.connect();
 catch (MulticasterInitException e) 
  //Handle exception...


multicast.joinGroup();
System.out.print(multicast.recieveData());

【问题讨论】：

由于问题与http://***.com/questions/8471447/java-multicast-sample-program-is-unable-to-deliver-packets-within-lan-across-ho有关，您可以参考我的cmets

【参考方案1】：

我之前遇到过类似的问题，必须确保在接收端指定了 NetworkInterface。

SocketAddress socketAddress = new InetSocketAddress(groupIp, groupPort);
NetworkInterface networkInterface = NetworkInterface.getByName(interfaceName);

socket.joinGroup(socketAddress, networkInterface);

其中interfaceName 是在 Linux 或 Mac 上运行 ifconfig 时显示的接口名称之一。

【讨论】：

你能给我关于***.com/questions/45162552/…我的问题的建议吗？

SocketAddress 是抽象类，不能新建 SocketAddress。

示例已更改。