java - UDP 网络中的绑定(bind)错误

Question

在我的服务器客户端程序中，通过 UDP，我的服务器接收消息，将该消息显示到控制台并从客户端显示，然后再次将其发送到客户端。

这是我的服务器，它从命令行输入其名称

import java.io.IOException;
import java.net.*;

class Stest implements Runnable {
private String str[];
DatagramSocket sock;
DatagramPacket pack;
String Sname;

Stest(String str[]) throws SocketException, UnsupportedEncodingException, IOException {
    this.str = str;
    this.Sname = str[0];
    System.out.println(Sname);
    new Thread(this).start();
}

public void run() {
    while (true) {
        byte[] data = new byte[1024];
        try {
            sock = new DatagramSocket(5050);
        } catch (SocketException ex) {
            Logger.getLogger(test.class.getName()).log(Level.SEVERE, null, ex);
        }
        pack = new DatagramPacket(data, data.length);
        try {
            sock.receive(pack);
        } catch (IOException e) {
            e.printStackTrace();
        }
        String s = null;
        try {
            s = new String(pack.getData(), "UTF-8");
            System.out.println(s);
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
        DatagramPacket dp = null;
        try {
            dp = new DatagramPacket(s.getBytes("UTF-8"), s.getBytes("UTF-8").length);
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
        dp.setPort(1);
        dp.setAddress(pack.getAddress());
        try {
            sock.send(dp);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

}

public class test{
public static void main(String[] args) {
    try {
       Stest stest= new Stest(args);

    } catch (IOException ex) {
        Logger.getLogger(test.class
                .getName()).log(Level.SEVERE, null, ex);
    }
}
}

这是我的客户端，它获取其名称、监听端口、服务器 IP 地址和服务器名称，并向服务器发送消息，并再次从服务器接收该消息，并将该消息显示到控制台。

import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;

class UDPClient {
String username;
String listening_port;
String serverAddress;
String servername;
public UDPClient(String username, String listening_port, String serverAddress, String servername) {
    this.username = username;
    this.listening_port = listening_port;
    this.serverAddress = serverAddress;
    this.servername = servername;
}
}
class ClientListen extends UDPClient implements Runnable {
Thread t;
DatagramSocket clientlistensocket;
DatagramPacket clientlistenpacket;
byte[] data;
public ClientListen(String username, String listening_port, String serverAddress, String servername) {
    super(username, listening_port, serverAddress, servername);
    try {
        clientlistensocket = new DatagramSocket(Integer.parseInt(listening_port));

    } catch (Exception e) {
        System.out.println(e + "    ClientListen");
    }
    t = new Thread(this, "ClientListen");
    t.start();
}

public void go() {
    String messag = new String(clientlistenpacket.getData());
    System.out.println(messag);
}

void processing() {
    data=new byte[1024];

    clientlistenpacket = new DatagramPacket(data,data.length);

    try {
        clientlistensocket.receive(clientlistenpacket);
        go();
    } catch (Exception e) {
        System.out.println(e + "   ClientlistenProcessing");
    }
}
public void run() {
    while (true) {
        try {
            processing();
        } catch (Exception e) {
            System.out.println(e + "Processing+run");
        }
    }
}

}
class ClientSpeak extends UDPClient {

DatagramPacket clientspeakpacket;
DatagramSocket clientspeaksocket;
InetAddress ipAddress;
Thread t;

public ClientSpeak(String username, String listening_port, String serverAddress, String servername) {
    super(username, listening_port, serverAddress, servername);

    try {

        clientspeaksocket = new DatagramSocket();

    } catch (Exception e) {
        System.out.println(e + "ClientSpeak");
    }
    try {

        String firstmessage = "Via:" + servername + "To:" + servername + "From:" + username + "Port:" + listening_port;
        byte[] firstdata = firstmessage.getBytes();
        ipAddress = InetAddress.getByName(serverAddress);

        clientspeakpacket = new DatagramPacket(firstdata, firstdata.length, ipAddress, 5050);
        clientspeaksocket.send(clientspeakpacket);
    } catch (Exception e) {
        System.out.println(e + "Clientspeak");
    }
}


}

public class testC {

public static void main(String[] args) {
    if (args.length == 4) {
        String username = args[0].trim();
        String listening_port = args[1].trim();
        String serverAddress = args[2].trim();
        String servername = args[3].trim();

        ClientSpeak clientSpeak = new ClientSpeak(username, listening_port, serverAddress, servername);
        ClientListen clientListen = new ClientListen(username, listening_port, serverAddress, servername);
    }
}
}

但它总是显示错误，例如:

S
Via:STo:SFrom:nahPort:1                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
Nov 21, 2016 7:20:34 PM Stest run
SEVERE: null
java.net.BindException: Address already in use: Cannot bind
at java.net.DualStackPlainDatagramSocketImpl.socketBind(Native Method)
at    java.net.DualStackPlainDatagramSocketImpl.bind0(DualStackPlainDatagramSocketImpl.java:84)
at java.net.AbstractPlainDatagramSocketImpl.bind(AbstractPlainDatagramSocketImpl.java:93)
at java.net.DatagramSocket.bind(DatagramSocket.java:392)
at java.net.DatagramSocket.<init>(DatagramSocket.java:242)
at java.net.DatagramSocket.<init>(DatagramSocket.java:299)
at java.net.DatagramSocket.<init>(DatagramSocket.java:271)
at Stest.run(test.java:41)
at java.lang.Thread.run(Thread.java:745)

我应该做什么？

Answer 1

问题在于，在 while 循环内的服务器中，您不断尝试将新的数据报套接字绑定(bind)到端口 5050

try {
    sock = new DatagramSocket(5050);
} catch (SocketException ex) {
    Logger.getLogger(test.class.getName()).log(Level.SEVERE, null, ex);
}

第二次，服务器读取并处理UDP消息后，会尝试绑定(bind)，但会出现异常。

您只需在 while 循环之前创建并绑定(bind) UDP 套接字一次，然后在 while 循环内使用该套接字进行整个通信。