Client.java

import com.google.gson.Gson;

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

public class Client {
  public static void main(String[] args) throws IOException {
    Socket socket = new Socket("localhost",5000);
    DataOutputStream dataOutputStream = new DataOutputStream(socket.getOutputStream());
    Gson gson = new Gson();
    Request request = new Request("300");
    String jsonRequest = gson.toJson(request);
    dataOutputStream.writeUTF(jsonRequest);
    dataOutputStream.flush();
    dataOutputStream.close();
    socket.close();
  }
}

gradle.txt

dependencies {
    implementation 'com.google.code.gson:gson:2.9.0'
}

Server.java

import com.google.gson.Gson;

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

public class Server {
  public static void main(String[] args) throws IOException {
    ServerSocket serverSocket = new ServerSocket(5000);
    Socket socket = serverSocket.accept();
    DataInputStream dataInputStream = new DataInputStream(socket.getInputStream());
    String jsonRequest = dataInputStream.readUTF();
    Gson gson = new Gson();
    Request request = gson.fromJson(jsonRequest,Request.class);
    System.out.println(request.requestCode);
    dataInputStream.close();
    socket.close();
  }
}