Problems with Sockets

Question

I’m creating an app that needs send and receive information of a web page through Sockets, the server in Java I managed to do, but I do not know much about JS, could help me to do the client that sends and receives messages in Javascript for web and connect to this Java server I made?

Server code: Java server.

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

    System.out.println("Inicia servidor.");

    ServerSocket server = new ServerSocket(3000);

    System.out.println("Aguardando conexão.");

    Socket socket = server.accept();

    System.out.println("Conexão estabelecida.");

    InputStream input = socket.getInputStream();
    OutputStream output = socket.getOutputStream();

    BufferedReader in = new BufferedReader(new InputStreamReader(input));
    PrintStream out = new PrintStream(output);

    while (true) {
        String mensagem = in.readLine();

        System.out.println(
                "Mensagem recebida do cliente [" +
                        socket.getInetAddress().getHostName() +
                        "]: " +
                        mensagem);
        if ("FIM".equals(mensagem)){
            break;
        }

        out.println(mensagem);
    }

    System.out.println("Encerrando conexão.");

    in.close();

    out.close();

    socket.close();

    System.out.println("Encerrando servidor.");

    server.close();

}

Answer 1

There are several ways to do this and ready libs. I’ll put here an example js native.

function WebSocketTest()
         {
            if ("WebSocket" in window)
            {
               alert("WebSocket is supported by your Browser!");

               // Let us open a web socket
               var ws = new WebSocket("ws://localhost:3000");

               ws.onopen = function()
               {
                  // Web Socket is connected, send data using send()
                  ws.send("Message to send");
                  alert("Message is sent...");
               };

               ws.onmessage = function (evt) 
               { 
                  var received_msg = evt.data;
                  alert("Message is received...");
               };

               ws.onclose = function()
               { 
                  // websocket is closed.
                  alert("Connection is closed..."); 
               };

               window.onbeforeunload = function(event) {
                  socket.close();
               };
            }

            else
            {
               // The browser doesn't support WebSocket
               alert("WebSocket NOT supported by your Browser!");
            }
         }

In this function it checks whether your browser supports Websocket. Then it opens the connection in the url you should configure.

ws.onopen is the event that happens as soon as you log into the socket.

ws.onmessage is the event when you receive a message

ws.onclose is the event when the connection is closed