STOMP events can be routed to @controller classes. For example, we will want methods which can be exposed to the client to add user to the chat or send message.

ChatRoomController.java

package com.nulpointerexception.npechatroom;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.messaging.handler.annotation.DestinationVariable;
import org.springframework.messaging.handler.annotation.MessageMapping;
import org.springframework.messaging.handler.annotation.Payload;
import org.springframework.messaging.handler.annotation.SendTo;
import org.springframework.messaging.simp.SimpMessageHeaderAccessor;
import org.springframework.messaging.simp.SimpMessageSendingOperations;
import org.springframework.stereotype.Controller;

import static java.lang.String.format;

@Controller
public class ChatRoomController {

    private static final Logger logger = LoggerFactory.getLogger(ChatRoomController.class);
    @Autowired
    private SimpMessageSendingOperations messagingTemplate;

    @MessageMapping("/chat/{roomId}/sendMessage")
    public void sendMessage(@DestinationVariable String roomId, @Payload Message chatMessage) {
        logger.info(roomId+" Chat messahe recieved is "+chatMessage.getContent());
        messagingTemplate.convertAndSend(format("/chat-room/%s", roomId), chatMessage);
    }

    @MessageMapping("/chat/{roomId}/addUser")
    public void addUser(@DestinationVariable String roomId, @Payload Message chatMessage,
                        SimpMessageHeaderAccessor headerAccessor) {
        String currentRoomId = (String) headerAccessor.getSessionAttributes().put("room_id", roomId);
        if (currentRoomId != null) {
            Message leaveMessage = new Message();
            leaveMessage.setType(Message.MessageType.LEAVE);
            leaveMessage.setSender(chatMessage.getSender());
            messagingTemplate.convertAndSend(format("/chat-room/%s", currentRoomId), leaveMessage);
        }
        headerAccessor.getSessionAttributes().put("name", chatMessage.getSender());
        messagingTemplate.convertAndSend(format("/chat-room/%s", roomId), chatMessage);
    }
}