ChatClient.java

package chat;

import com.example.chat.ChatServiceGrpc.*;
import com.example.chat.ChatServiceGrpc;
import com.example.chat.ChatServiceOuterClass.*;
import io.grpc.ManagedChannel;
import io.grpc.ManagedChannelBuilder;
import io.grpc.stub.StreamObserver;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class ChatClient {

    public final static String IP = "localhost";
    public final static int PORT = 1337;

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

        //buffered reader to read from standard input
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        //simply asking the nickname
        String nickname;

        System.out.println("What's your nickname?");
        nickname = br.readLine();


        System.out.println("---------");
        System.out.println("[CHAT CLIENT] Connecting to chat server @ "+IP+":"+PORT);

        //opening a connection with chat server

        final ManagedChannel channel = ManagedChannelBuilder.forTarget(IP+":"+PORT).usePlaintext().build();

        System.out.println("[CHAT CLIENT] Connected!");

        System.out.println("[CHAT CLIENT] Establishing stream from server...");

        //creating the asynchronous stub

        ChatServiceStub stub = ChatServiceGrpc.newStub(channel);

        //the stub returns a stream (to communicate with the server, and thus with all the other clients).
        //the argument is the stream of messages which are transmitted by the server.

        StreamObserver<ChatMessage> serverStream = stub.chat(new StreamObserver<ChatMessage>() {

            //remember: all the methods here are CALLBACKS which are handled in an asynchronous manner.

            //we define what to do when a message from the server arrives (just print the message)
            public void onNext(ChatMessage chatMessage) {

                String from = chatMessage.getFrom();
                String message = chatMessage.getMessage();

                System.out.println("\n"+from+" -> "+message);

            }

            public void onError(Throwable throwable) {

            }

            public void onCompleted() {

            }
        });


        System.out.println("[CHAT CLIENT] Now you can chat :)");


        //dumb code to handle the chat
        //it is a while loop which reads the message
        while(true){

            String message = br.readLine();

            //if the message is quit
            if(message.equals("quit")){
                //we communicate to the server that we are done and we exit the loop
                serverStream.onCompleted();
                break;
            }

            //we use the stream to communicate to the server our message.
            serverStream.onNext(ChatMessage.newBuilder().setFrom(nickname).setMessage(message).build());

        }


        System.out.println("Goodbye!");
    }

}