Socket between 2 devices

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Socket between 2 devices

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I would like to send data between different machines, between 2 computers, between a computer and an Android .

I made the example internally, on the same computer, but when I disconnect (the server stays on one computer and the client goes to another one, it does not work).

Server:

public static void main(String[] args) {
        try {
            // Instancia o ServerSocket ouvindo a porta 12345
            ServerSocket servidor = new ServerSocket(12345);
            System.out.println("Servidor ouvindo a porta 12345");
           // servidor.bind(new InetSocketAddress("192.168.5.1", 0));

            InetAddress inet = servidor.getInetAddress();
            System.out.println("HostAddress="+inet.getHostAddress());
            System.out.println("HostName="+inet.getHostName());
            while(true) {
              // o método accept() bloqueia a execução até que
              // o servidor receba um pedido de conexão
              Socket cliente = servidor.accept();
              System.out.println("Cliente conectado: " + cliente.getInetAddress().getHostAddress());
              ObjectOutputStream saida = new ObjectOutputStream(cliente.getOutputStream());
              saida.flush();
              saida.writeObject(new Date());
              saida.close();
              cliente.close();
            }  
        }   
        catch(Exception e) {
            System.out.println("Erro: " + e.getMessage());
        }
    }

Client:

public static void main(String[] args) {
        try {
             Socket cliente = new Socket("0.0.0.0",12345);
            InetAddress inet = cliente.getInetAddress();
            System.out.println("HostAddress="+inet.getHostAddress());
            System.out.println("HostName="+inet.getHostName());
            ObjectInputStream entrada = new ObjectInputStream(cliente.getInputStream());
            Date data_atual = (Date)entrada.readObject();
            JOptionPane.showMessageDialog(null,"Data recebida do servidor:" + data_atual.toString());
            entrada.close();
            System.out.println("Conexão encerrada");
        }
        catch(Exception e) {
          System.out.println("Erro: " + e.getMessage());
        }
    }

The strange thing is that the server output is:

Servidor ouvindo a porta 12345
HostAddress=0.0.0.0
HostName=0.0.0.0

Then when I try to put the client on another computer it does not work, even if I insert the IP where the server is.

Note: The machines are on different networks.

Obs :

java socket

asked by anonymous 26.08.2018 / 21:18

2 answers

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score 0 · Answer 1

In the client you need to pass the IP address or hostname of the server.

Socket cliente = new Socket("0.0.0.0",12345);  // <<< errado

I do not know Java, but the above line should be

Socket cliente = new Socket("127.0.0.1",12345);  // <<< mesma máquina

or

Socket cliente = new Socket("10.172.36.130",12345);  // <<< outra máquina

where "10.172.36.130" is just an example, you need to replace with the IP (or name) of the machine where your server is running.

score 0 · Answer 2

About the server output:

The output is correct, since you did not specify which IP was to bind, it bound all of the network interface.

About the code:

Socket cliente = new Socket("0.0.0.0",12345);

I just changed the "0.0.0.0" to the IP of my remote server and the code worked correctly. You should have some firewall blocking.