// Protocol - Calculation
// => Json(Gson) 
//   [op: char ][lhs: int][rhs: int ]
//   '+', '-' , '*'
public class Packet {
  private char op;
  private int lhs;
  private int rhs;

  Packet(char op, int lhs, int rhs) {
    this.op = op;
    this.lhs = lhs;
    this.rhs = rhs;
  }

  public char getOp() {
    return op;
  }

  public int getLhs() {
    return lhs;
  }

  public int getRhs() {
    return rhs;
  }
}

import com.google.gson.Gson;
import gson.Packet;

import java.io.DataInputStream;
import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;
import java.net.ServerSocket;
import java.net.Socket;

// Protocol - Calculation
// => Json(Gson)
//   [op: char ][lhs: int][rhs: int ]
//   '+', '-' , '*'
public class Server {
  public static void main(String[] args) {
    try {
      ServerSocket serverSocket = new ServerSocket(5000);
      Socket socket = serverSocket.accept();
        try (InputStream is = socket.getInputStream();
             DataInputStream dis = new DataInputStream(is)) {

          int count = 0;
          while (true) {
            byte[] data = new byte[1024];
            int packetLen;
            try {
              packetLen = dis.readInt();
            } catch (EOFException e) {
              break;
            }

            int ret = is.read(data, 0, packetLen);
            if (ret == -1) {
              break;
            }

            String json = new String(data, 0, packetLen); 
            Gson gson = new Gson();
            Packet packet = gson.fromJson(json, Packet.class);
            System.out.printf("[%5d] %d %c %d\n", count++, packet.getLhs(), packet.getOp(), packet.getRhs());

          }
        }
    } catch (IOException e) {
      e.printStackTrace();
    }
  }
}

import com.google.gson.Gson;
import gson.Packet;

import java.io.DataOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.Socket;

public class Client {

  public static void main(String[] args) {

    Packet packet = new Packet('+', 10, 20);
    Gson gson = new Gson();
    String json = gson.toJson(packet);

    try {
      Socket socket = new Socket("127.0.0.1", 5000);

      try (OutputStream os = socket.getOutputStream();
           DataOutputStream dos = new DataOutputStream(os)) {
        
		for (int i = 0; i < 100000; i++) {
          byte[] data = json.getBytes();
          int len = data.length;
          dos.writeInt(len);
          os.write(data, 0, len);
        }
      }
    } catch (IOException e) {
      e.printStackTrace(); 
    }
  }
}