java - 客户端中的 DatagramSocket 未绑定(bind)到服务器中的端口。端口已被使用

Question

我有一台服务器等待客户端通过 DatagramSocket 发送数据包。但是当我在客户端使用与服务器相同的端口(以便它们可以通信)时，我在客户端得到一个异常:

Exception in thread "main" java.net.BindException: Address already in use: Cannot bind
at java.net.DualStackPlainDatagramSocketImpl.socketBind(Native Method)
at java.net.DualStackPlainDatagramSocketImpl.bind0(DualStackPlainDatagramSocketImpl.java:80)
at java.net.AbstractPlainDatagramSocketImpl.bind(AbstractPlainDatagramSocketImpl.java:93)
at java.net.DatagramSocket.bind(DatagramSocket.java:372)
at java.net.DatagramSocket.<init>(DatagramSocket.java:222)
at java.net.DatagramSocket.<init>(DatagramSocket.java:279)
at tp.Repositorio.main(Cliente.java:146)

所以在服务器端我有一个等待数据包的线程。像这样:

addr = InetAddress.getByName("localhost");
DatagramSocket socket = new DatagramSocket(5008, addr);
DatagramPacket packet = new DatagramPacket(buff, buff.length);
 while(true)
    {
      s.receive(packet);
// and then it throws another thread to treat the packet...
    }

在客户端我有这样的东西:

 InetAddress inet;
 inet = InetAddress.getByName("localhost");
 s_data = new DatagramSocket(5008, inet);

我试图改变双方的端口，但它也给了我这个异常(exception)。如果我将端口更改为例如服务器中的 5003 和客户端中的 5004，它不会给我任何异常(当然)但它们无法相互连接。

你们有解决这个问题的想法吗？

谢谢。

编辑:

这是以下客户端代码(称为 repositorio):

/*
* To change this license header, choose License Headers in Project Properties.
* To change this template file, choose Tools | Templates
* and open the template in the editor.
*/
package tp;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.IOException;
import java.io.ObjectOutput;
import java.io.ObjectOutputStream;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.Inet4Address;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 *
 * @author Diogo
 */
public class Repositorio {
    static int nr_ligacoes;
    static int porto;
    static String endereco;


    Repositorio(int pt, String end)
    {
        this.porto = pt;
        this.endereco = end;
    }

    public static void setNr_ligacoes(int nr_ligacoes) {
        Repositorio.nr_ligacoes = nr_ligacoes;
    }

    public static void setPorto(int porto) {
        Repositorio.porto = porto;
    }

    public static void setEndereco(String endereco) {
        Repositorio.endereco = endereco;
    }



    public File[] getFicheiros()
    {
        File folder = new File("C:\\temp2");

        File[] ficheiros = folder.listFiles();


        for (int i = 0; i < ficheiros.length; i++) {
            if (ficheiros[i].isFile()) {
                System.out.println("File " + ficheiros[i].getName());
            } else if (ficheiros[i].isDirectory()) {
                System.out.println("Directory " + ficheiros[i].getName());
            }
        }

        return ficheiros;
    }

    public int getNr_ligacoes() {
        return nr_ligacoes;
    }


    public int getPorto() {
        return porto;
    }

    public String getEndereco() {
        return endereco;
    }

    public ArrayList<String> getListadeFicheiros()
    {
        ArrayList<String> fich_nome = new ArrayList<>();
        File[] fich = getFicheiros();

        for(int i = 0; i <fich.length ; i++)
            fich_nome.add(fich[i].getName());

        return fich_nome;
    }

    public boolean VerFicheiro(String nome)
    {
        File[] fich = getFicheiros();


        for(int i = 0; i<fich.length;i++)
            if(nome.compareTo(fich[i].getName()) == 0)
                return true;
        return false;
    }




    public static void main(String[] args) throws IOException
    {
        ServerSocket socket_r;
        File localDirectory;
        DatagramSocket s_data;
        DatagramPacket p;


        /* if(args.length != 4){
        System.out.println("Sintaxe: java Repositorio serverTcpPort serverAddress localDirectory");
        return;
        }  */

        localDirectory = new File("C:\\temp2");

        if(!localDirectory.exists()){
            System.out.println("A directoria " + localDirectory + " nao existe!");
            return;
        }

        if(!localDirectory.isDirectory()){
            System.out.println("O caminho " + localDirectory + " nao se refere a uma directoria!");
            return;
        }

        if(!localDirectory.canWrite()){
            System.out.println("Sem permissoes de escrita na directoria " + localDirectory);
            return;
        }

        //Repositorio r = new Repositorio(5002,"localhost");
        InetAddress inet;
        inet = InetAddress.getByName("localhost");
        socket_r = new ServerSocket(5003);

        new lancaRepositorioCliente(socket_r, localDirectory).start();

        s_data = new DatagramSocket(5008, inet);

        new lancarepositorioServidor(s_data, localDirectory).start();


    }




    static class lancarepositorioServidor extends Thread{

        DatagramSocket s;
        File localDirectory;
        ListadeRepositorios listaRep;

        lancarepositorioServidor(DatagramSocket s_data, File local)
        {
            this.localDirectory = local;
            this.s = s_data;
        }

        @Override
        public void run() {
            System.out.println("Estou no lanca to servidor");
            byte[] buf = new byte[10000];
            DatagramPacket pack = new DatagramPacket(buf, 128);

            new repositorioToServidor(pack,s).start();

        }

    }
    static class repositorioToServidor extends Thread{
        DatagramPacket pack;
        DatagramSocket s;

        public repositorioToServidor(DatagramPacket packet, DatagramSocket s) {
            this.pack = packet;
            this.s = s;

        }

        @Override
        public void run() {

            while(true)
            {
                try {
                    sleep(10000);
                } catch (InterruptedException ex) {
                    Logger.getLogger(Repositorio.class.getName()).log(Level.SEVERE, null, ex);
                }
                ByteArrayOutputStream bos = new ByteArrayOutputStream(2048);
                ObjectOutputStream oos;
                try {
                    oos = new ObjectOutputStream(bos);
                    oos.writeObject(new Notificacao(nr_ligacoes));

                    DatagramPacket packet = new DatagramPacket(bos.toByteArray(), bos.size());
                    s.send(packet);

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


            }


        }


    }


    static class repositorioToCliente extends Thread{
        Socket s;
        File localDirectory;

        public repositorioToCliente(Socket s, File local) {
            this.s = s;
            this.localDirectory = local;
        }

        public Socket getS() {
            return s;
        }

        @Override
        public void run() {

            System.out.println("Estou no lanca to cliente");


        }


    }


    static class lancaRepositorioCliente extends Thread{
        ServerSocket s;
        File localDirectory;

        public lancaRepositorioCliente(ServerSocket s, File local) {
            this.s = s;
            this.localDirectory = local;
        }

        public ServerSocket getS() {
            return s;
        }

        @Override
        public void run() {
            Socket sClient;

            while(true)
            {
                try {
                    sClient = s.accept();

                    new repositorioToCliente(sClient,localDirectory).start();
                    // vamos aqui receber o ficheiro que é para eliminar/depositar

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

        }


    }

}

服务器代码:

    package tp;

/*
* To change this license header, choose License Headers in Project Properties.
* To change this template file, choose Tools | Templates
* and open the template in the editor.
*/

import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.PrintWriter;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.nio.charset.Charset;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;


/**
 *
 * @author Diogo
 */
public class Servidor{

    protected File localDirectory;
    static String LoginfileName;
    //List <Repositorio> rep = null;
    static ListadeRepositorios listaRep;
    static ArrayList <String> ficheiros = null;

    public Servidor()
    {
        this.ficheiros = new ArrayList<>();
    }

    public void setFicheiros(List <String> a)
    {
        a.stream().forEach((a1) -> {
            ficheiros.add(a1);
        });
    }

    public static void main(String[] args) throws IOException
    {
        Servidor s = new Servidor();
        ListadeRepositorios lista_rep = new ListadeRepositorios();
        int listeningPort1;
        int listeningPort2;
        ServerSocket serverSocket;
        InetAddress addr;
        DatagramSocket socket;

        try {

            //listeningPort = Integer.parseInt(args[0]);
            listeningPort1 = 5001;
            listeningPort2 = 5008;

            if(listeningPort1 <= 0) throw new NumberFormatException("Porto TCP de escuta indicado <= 0 (" + listeningPort1 + ")");


            LoginfileName = "c:/temp/users.txt";

            serverSocket = new ServerSocket(listeningPort1);

            serverSocket.setSoTimeout(1000000000);

            new lancaCliente(serverSocket, LoginfileName).start();

            addr = InetAddress.getByName("localhost");
            socket = new DatagramSocket(listeningPort2, addr);


            new lancaRepositorio(socket).start();


        }catch(NumberFormatException e){
            System.out.println("O porto de escuta deve ser um inteiro positivo.");
        }
    }


    static class lancaCliente extends Thread{

        ServerSocket s;
        String Login;

        public lancaCliente(ServerSocket s, String Login) {

            this.s = s;
            this.Login = Login;
        }

        @Override
        public void run() {
            Socket accept;

            while(true)
            {
                try {

                    System.out.println("Servidor à espera de clientes: ");


                    accept = s.accept();
                    System.out.println("Servidor aceitou Cliente");

                    new atendeCliente(accept, this.Login).start();


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


            }

        }

    }

    static class atendeCliente extends Thread{

        int porto;
        //List<Repositorio> repositorios;
        List<String> clienteLogado;
        //List<Socket> socketsAbertos;
        List<String> infoFicheiros;
        Socket Scliente;
        List<String> lines;
        String arg0 = null,arg1 = null, arg2=null;
        String[] comando;
        String filename;
        ListadeRepositorios listaRep2;


        public static final int TIMEOUT = 5; //segundos

        atendeCliente(Socket s, String nome)
        {
            this.Scliente = s;
            this.filename = nome;
        }



        protected int processaLogin(String user, String pass) throws IOException
        {
            String separaUser = null, separaPass=null;
            String[] separa;

            Path caminho = Paths.get("C:/temp/users.txt");

            Charset charset = Charset.forName("ISO-8859-1");

            try {
                lines = Files.readAllLines(caminho, charset);

                lines.stream().forEach((line) -> {
                    System.out.println(line);
                });
            } catch (IOException e) {
                System.out.println(e);
            }

            for(int i = 0; i<lines.size();i++)
            {
                separa = lines.get(i).split("\\s+");
                separaUser = separa[0];
                separaPass = separa[1];

                if(user.compareTo(separaUser) == 0 && pass.compareTo(separaPass)==0)
                    return 1;
            }
            return 0;

        }


        @Override
        public void run()
        {
            BufferedReader buf = null;
            PrintWriter escreve = null;
            int estaLogado;
            String mensagem = "";

            try {
                buf = new BufferedReader(new InputStreamReader(Scliente.getInputStream()));
            } catch (IOException ex) {
                Logger.getLogger(atendeCliente.class.getName()).log(Level.SEVERE, null, ex);
            }
            try {
                escreve = new PrintWriter(Scliente.getOutputStream());
            } catch (IOException ex) {
                Logger.getLogger(atendeCliente.class.getName()).log(Level.SEVERE, null, ex);
            }

            try {
                while(true)
                {
                    try {
                        buf = new BufferedReader(new InputStreamReader(Scliente.getInputStream()));
                    } catch (IOException ex) {
                        Logger.getLogger(atendeCliente.class.getName()).log(Level.SEVERE, null, ex);
                    }

                    System.out.println("Estou a espera de uma mensagem do cliente");
                    mensagem = buf.readLine();

                    System.out.println("Recebi: " + mensagem);
                    comando = mensagem.split("\\s+");
                    arg0  = comando[0];
                    arg1  = comando[1];
                    arg2  = comando[2];
                    System.out.println(comando[0] + comando[1] + comando[2]);
                    System.out.println(arg0 + arg1 + arg2);
                    if("login".compareTo(arg0)==0)
                    {
                        estaLogado = processaLogin(arg1, arg2);
                        if (estaLogado == 0)
                        {
                            escreve.println("Nao existe!");
                            escreve.flush();
                        }
                        else
                        {
                            escreve.println("LoginFeito");
                            escreve.flush();
                        }
                    }

                    else if("deposita".compareTo(arg0)==0 || "apaga".compareTo(arg0) == 0)
                    {
                        Repositorio rep;
                        rep = listaRep2.MenosCongest();
                        int porto_rep = rep.getPorto();
                        String end_rep = rep.getEndereco();
                        String porto_s = Integer.toString(porto_rep);
                        String comandoToCliente = end_rep + " " + porto_s;

                        escreve.println(comandoToCliente);
                        escreve.flush();
                    }

                    else if("listaficheiros".compareTo(arg0) == 0)
                    {
                        ObjectOutputStream outB = new ObjectOutputStream(Scliente.getOutputStream());
                        ficheiros.add("f1.txt");
                        ficheiros.add("f2.txt");
                        ficheiros.add("f3.txt");
                        ficheiros.add("f4.txt");

                        //ficheiros_disponiveis = listaRep.getFicheiros();

                        outB.writeObject(ficheiros);
                        outB.flush();
                    }

                    mensagem = "";
                }



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

        }

    }


    static class lancaRepositorio extends Thread{

        DatagramSocket ser;
        ListadeRepositorios listaRep;

        public lancaRepositorio(DatagramSocket s)
        {
            this.ser = s;
        }


        @Override
        public void run() {

            byte[] buff = new byte[1024];

            DatagramSocket s = this.ser;
            DatagramPacket packet = new DatagramPacket(buff, buff.length);
            Repositorio r;

            while(true)
            {
                try {
                    System.out.println("Sevidor à espera de repositorios:");
                    s.receive(packet);
                    System.out.println("Sevidor recepbeu repositorios");
                    r = new Repositorio(packet.getPort(),packet.getAddress().getHostAddress());

                    listaRep.addRepositorio(r);
                    new atendeRepositorio(s,r).start();



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

        }

    }



    static class atendeRepositorio extends Thread{

        DatagramSocket so;
        Repositorio r;

        public atendeRepositorio(DatagramSocket s, Repositorio r)
        {
            this.so = s;
            this.r = r;
        }

        @Override
        public void run() {
            while(true)
            {
                try {
                    byte[] incomingData = new byte[1024];
                    DatagramPacket incomingPacket = new DatagramPacket(incomingData, incomingData.length);

                    so.receive(incomingPacket);

                    byte[] data = incomingPacket.getData();

                    ByteArrayInputStream in;
                    in = new ByteArrayInputStream(data);

                    try (ObjectInputStream iStream = new ObjectInputStream(new ByteArrayInputStream(data))) {
                        Notificacao n1 = (Notificacao) iStream.readObject();

                        for(int i = 0;i<listaRep.getListaRepositorios().size();i++)
                        {
                            if(r == listaRep.getListaRepositorios().get(i))
                            {
                                r.setNr_ligacoes(n1.getN_op());
                            }

                        }

                    }


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



    }



}

Answer 1

在遍历 Java Network Programming Book's Chapter 12. UDP 时，我发现了以下关于 DatagramSocket 的信息:-

All datagram sockets bind to a local port, on which they listen forincoming data and which they place in the header of outgoingdatagrams. If you’re writing a client, you don’t care what the localport is, so you call a constructor that lets the system assign anunused port (an anonymous port). This port number is placed in anyoutgoing data‐ grams and will be used by the server to address anyresponse datagrams.

If you’re writing a server, clients need to knowon which port the server is listening for incoming data‐ grams;therefore, when a server constructs a DatagramSocket, it specifies thelocal port on which it will listen. However, the sockets used byclients and servers are otherwise identical: they differ only inwhether they use an anonymous (system-assigned) or a well-known port.There’s no distinction between client sockets and server sockets, asthere is with TCP. There’s no such thing as a DatagramServerSocket.

解决方案:-

您可能对这两个端口感到困惑。客户端的 DatagramSocket 应该使用匿名端口，而您发送到服务器的数据包应该使用服务器的端口发送到服务器。两者是不同的东西。这可能根本不会生成 BindException。

只需在您的 Cliente.java 中使用以下构造函数调用来创建客户端套接字:-

DatagramSocket socket = new DatagramSocket();

发往服务器的数据报包应该使用与服务器相同的端口号:-

DatagramPacket packet = new DatagramPacket(buf, buf.length, 
                            address, 5008);    // server's port number is 5008
socket.send(packet);

我希望这有助于解决您的问题...