UDP 打孔 Java 示例

我想在具有静态IP的服务器的帮助下，与两个客户端进行UDP打孔。服务器等待端口 7070 和 7071 上的两个客户端。之后，它将IP地址和端口相互发送。这部分工作正常。但是我无法在两个客户端之间建立通信。我在不同的Wifi网络和3G移动网络中尝试了该代码。客户端程序引发 IO 异常“没有到主机的路由”。客户端代码用于两个客户端。一次使用端口 7070 执行，一次使用 7071 执行。

您认为我是否正确实现了UDP打孔概念？有什么想法可以让它工作吗？下面首先是服务器代码，然后是客户端代码。

感谢您的帮助。

服务器代码：

public class UDPHolePunchingServer {

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

    // Waiting for Connection of Client1 on Port 7070
    // ////////////////////////////////////////////////

    // open serverSocket on Port 7070
    DatagramSocket serverSocket1 = new DatagramSocket(7070);

    System.out.println("Waiting for Client 1 on Port "
            + serverSocket1.getLocalPort());

    // receive Data
    DatagramPacket receivePacket = new DatagramPacket(new byte[1024], 1024);
    serverSocket1.receive(receivePacket);

    // Get IP-Address and Port of Client1
    InetAddress IPAddress1 = receivePacket.getAddress();
    int port1 = receivePacket.getPort();
    String msgInfoOfClient1 = IPAddress1 + "-" + port1 + "-";

    System.out.println("Client1: " + msgInfoOfClient1);

    // Waiting for Connection of Client2 on Port 7071
    // ////////////////////////////////////////////////

    // open serverSocket on Port 7071
    DatagramSocket serverSocket2 = new DatagramSocket(7071);

    System.out.println("Waiting for Client 2 on Port "
            + serverSocket2.getLocalPort());

    // receive Data
    receivePacket = new DatagramPacket(new byte[1024], 1024);
    serverSocket2.receive(receivePacket);

    // GetIP-Address and Port of Client1
    InetAddress IPAddress2 = receivePacket.getAddress();
    int port2 = receivePacket.getPort();
    String msgInfoOfClient2 = IPAddress2 + "-" + port2 + "-";

    System.out.println("Client2:" + msgInfoOfClient2);

    // Send the Information to the other Client
    // /////////////////////////////////////////////////

    // Send Information of Client2 to Client1
    serverSocket1.send(new DatagramPacket(msgInfoOfClient2.getBytes(),
            msgInfoOfClient2.getBytes().length, IPAddress1, port1));

    // Send Infos of Client1 to Client2
    serverSocket2.send(new DatagramPacket(msgInfoOfClient1.getBytes(),
            msgInfoOfClient1.getBytes().length, IPAddress2, port2));

    //close Sockets
    serverSocket1.close();
    serverSocket2.close();
}

客户端代码

public class UDPHolePunchingClient {

    public static void main(String[] args) throws Exception {
    // prepare Socket
    DatagramSocket clientSocket = new DatagramSocket();

    // prepare Data
    byte[] sendData = "Hello".getBytes();

    // send Data to Server with fix IP (X.X.X.X)
    // Client1 uses port 7070, Client2 uses port 7071
    DatagramPacket sendPacket = new DatagramPacket(sendData,
            sendData.length, InetAddress.getByName("X.X.X.X"), 7070);
    clientSocket.send(sendPacket);

    // receive Data ==> Format:"<IP of other Client>-<Port of other Client>"
    DatagramPacket receivePacket = new DatagramPacket(new byte[1024], 1024);
    clientSocket.receive(receivePacket);

    // Convert Response to IP and Port
    String response = new String(receivePacket.getData());
    String[] splitResponse = response.split("-");
    InetAddress ip = InetAddress.getByName(splitResponse[0].substring(1));

    int port = Integer.parseInt(splitResponse[1]);

    // output converted Data for check
    System.out.println("IP: " + ip + " PORT: " + port);

    // close socket and open new socket with SAME localport
    int localPort = clientSocket.getLocalPort();
    clientSocket.close();
    clientSocket = new DatagramSocket(localPort);

    // set Timeout for receiving Data
    clientSocket.setSoTimeout(1000);

    // send 5000 Messages for testing
    for (int i = 0; i < 5000; i++) {

        // send Message to other client
        sendData = ("Datapacket(" + i + ")").getBytes();
        sendPacket = new DatagramPacket(sendData, sendData.length, ip, port);
        clientSocket.send(sendPacket);

        // receive Message from other client
        try {
            receivePacket.setData(new byte[1024]);
            clientSocket.receive(receivePacket);
            System.out.println("REC: "
                    + new String(receivePacket.getData()));

        } catch (Exception e) {
            System.out.println("SERVER TIMED OUT");
        }
    }

    // close connection
    clientSocket.close();
}

更新代码通常正常工作。我现在已经在两个不同的家庭网络中尝试过它，并且它正在工作。但它在我的3G或大学网络中不起作用。在3G中，我验证了NAT是否再次将两个端口（客户端端口和路由器分配的端口）映射在一起，即使在关闭并打开客户端Socket之后也是如此。有没有人知道为什么它不起作用呢？