DatagramSocket in Client not binding to the port in Server. Port already in use

Question

I have a server that is wating on clients to send a packet via DatagramSocket. But when in the Client i use the same ports as the Server (so that they can comunicate) i get an Exception in the Client side:

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.(DatagramSocket.java:222)
at java.net.DatagramSocket.(DatagramSocket.java:279)
at tp.Repositorio.main(Cliente.java:146)

So in the server side i have a thread that is wating on the packets. Something like this:

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...
    }

And on the client side i have something like this:

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

I tried to change the port in both sides but it also gave me this exception. If i change the ports to for example 5003 in the Server and 5004 in the Client, it doesn't give me any exception (of course) but they are unable to connect between each other.

You guys have any ideas in order to solve this?

Thanks.

Edit:

Here's the following Client code (it is called 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 getListadeFicheiros()
    {
        ArrayList fich_nome = new ArrayList<>();
        File[] fich = getFicheiros();

        for(int i = 0; i



Server Code:

    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  rep = null;
    static ListadeRepositorios listaRep;
    static ArrayList  ficheiros = null;

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

    public void setFicheiros(List  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 repositorios;
        List clienteLogado;
        //List socketsAbertos;
        List infoFicheiros;
        Socket Scliente;
        List 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

Am_I_Helpful · Accepted Answer

While going through Java Network Programming Book's Chapter 12. UDP, I found the following about the DatagramSocket :-

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

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

SOLUTION :-

You're probably confused between the two ports. The Client's DatagramSocket should use anonymous port whereas the packet which you're sending to server should be sent to the Server using server's port. Both are different things. This probably won't generate BindException at all.

Simply use the following constructor call in your Cliente.java for creating Client Socket:-

DatagramSocket socket = new DatagramSocket();

And the DatagramPacket destined for server should use the same port number as that of the server :-

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

I hope this helps and solves your problem...

DatagramSocket in Client not binding to the port in Server. Port already in use

Answers (1)

Related Questions