Sending and receiving messages in java

Question

I'm currently working on a TCP/IP socket request response system using java, I was able to setup some client/server interfaces where the client is able to send messages to the server and the server prints the message so the console. I want the server to also be able to send responses to the client and vis-versa. Is there a way possible I can achieve this ?

This is the client code

     import java.io.*;
    import java.net.ServerSocket;
    import java.net.Socket;
    
    public class Main {
        public static void main(String[] args) throws IOException {
            String localhost = "127.0.0.1";
            int port = 8091;
            sendMessage(localhost, port);
        }
    
        public static void sendMessage(String server, int port) throws IOException {
            // Client
            Socket socket = new Socket(server, port);
            DataOutputStream output = new DataOutputStream(socket.getOutputStream());
            BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));
    
            while(true){
                String input = bufferedReader.readLine();
                output.writeUTF(input);
                System.out.println("message sent " + input );
    //           receiveResponse(port);
                if(input.equalsIgnoreCase("exit"))
                    break;
    //            if(output.writeUTF(input)){}
            }
            socket.close();
    
        }
    
        public static void receiveResponse(int port) {
            try {
                ServerSocket serverSocket = new ServerSocket(port);
                Socket as = serverSocket.accept();
                DataInputStream in = new DataInputStream(as.getInputStream());
                String yoo = in.readUTF();
                System.out.println("Client: " + yoo);
                if(!yoo.isEmpty()){
                    System.out.println("message received");
                }
                if(yoo.equalsIgnoreCase("exit")){
                    System.out.println("Hello world");
                }
    
            } catch (Exception ex) {
                ex.printStackTrace();
            }
        }
    }```


Below is the server code

    ``` 
    import java.io.*;
    import java.net.ServerSocket;
    import java.net.Socket;
    
    public class Server {
        public static void main(String[] args) throws IOException {
            int port = 8091;
          receiveMessage(port);
    
        }
    
        public static void receiveMessage(int port) throws IOException {
            ServerSocket serverSocket = new ServerSocket(port);
            Socket as = serverSocket.accept();
            System.out.println("Connected");
            System.out.println("incoming = " + as.getInputStream());
            DataInputStream in = new DataInputStream(as.getInputStream());
    
    
    
            System.out.println(in.readUTF());
            // ==========================
    
            while(true){
                String yoo = in.readUTF();
                System.out.println("Client: " + yoo);
                if(!yoo.isEmpty()){
    //                sendResult();
                    System.out.println("message received");
                }
                if(yoo.equalsIgnoreCase("exit"))
                    break;
            }
            as.close();
        }
    
        public static void sendResult( ) {
            try {
                System.out.println("HELLO WORLD");
                System.out.println("Connected to client");
    //            ObjectOutputStream os = new ObjectOutputStream(as.getOutputStream());
    //
    //            os.writeObject(result);
    //            System.out.println("Result sent");
    
                String str = "Hello World";
                OutputStreamWriter osw;
                Socket socket = null;
                socket = new Socket("localhost", 8090);
                osw =new OutputStreamWriter(socket.getOutputStream(), "UTF-8");
                osw.write(str, 0, str.length());
            } catch (Exception ex) {
                ex.printStackTrace();
            }
        }
    }
    
    
     ```

Answer 1

All things being equal (starting from what you already have) you could do something like this:

        public static void receiveResponse(Socket socket) {
            try {                
                DataInputStream in = new DataInputStream(socket.getInputStream());
                String yoo = in.readUTF();
                System.out.println("Client: " + yoo);
                if(!yoo.isEmpty()){
                    System.out.println("message received");
                }
                if(yoo.equalsIgnoreCase("exit")){
                    System.out.println("Hello world");
                }
    
            } catch (Exception ex) {
                ex.printStackTrace();
            }
        }

Some things you'll need to look at a little:

• Replacing Main class with a Client class that manages the communication. This would allow you to maintain socket , inStream and outStream as instance variables.
• Maybe look at replacing DataInputStream with a more specific / consistent transfer protocol method (byte count, delimiter, etc).