如何从Java对象向客户端发送spring消息

Question

I need to send stomp messages from an object to my client using a SimpMessagingTemplate (or any message in the JSON format)

However my object is not a Controller and if I declare my class as a controller, my Spring boot application doesn't start due to a bean not set up.

I am creating a game for my bachelor thesis that is hosted on a Spring server. In my app I have rooms which each have a gameSession with one thread running.

I currently have a Class called which sends scheduled messages to the server like this

@Controller
public class RoomsController {
@Autowired
    private SimpMessagingTemplate template;

    @Scheduled(fixedRate = 500)
    public void updateRoomsInterface() throws Exception {
        Game.getInstance().getRooms().forEach((k,v) -> {
            if (v != null) {
                System.out.println("Ted posilam do room " + k + " ktery se jmenuje " + v.getName() + " cely seznam hracu, schvalne co mi prijde, ok?");
                Map <String, Player> playersList = v.getPlayers();
//              String message = v.getPlayers().get;
                this.template.convertAndSend("/topic/game/room/"+v.getID(), playersList);
            }
        });
    }
}

This is somewhat ok, but I need my GameSession objects to be independent of the server timer (because different games start at different times and I need to use ticks of the game)

My currently looks like this:

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.messaging.simp.SimpMessagingTemplate;

public class GameSession extends Thread {
    @Autowired
    private SimpMessagingTemplate template;
    private volatile boolean exit = false;
    private Room room;


    public GameSession(Room room) {
        this.room = room;
        status = "WAITING";
    }

    @Override
    public void run() {
        // dokud ne exit
        while (!false) {
            try {
                Thread.sleep(500);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            sendMessage();
        }
    }

    public void sendMessage() {
        System.out.println("Does this execute?");
        this.template.convertAndSend("/topic/game/room/"+room.getID()+"/session", "THIS IS A TEST");
    }
}

But when this executes, I get an Exception in thread

Does this execute?
Exception in thread "Thread-6" java.lang.NullPointerException
    at cz.vse.pavm07.bp.objects.GameSession.sendMessage(GameSession.java:65)
    at cz.vse.pavm07.bp.objects.GameSession.run(GameSession.java:34)

I need each gameSession to send the messages directly from the gameSession objects because of the ticks.

What am I doing wrong?

Answer 1

Your GameSession is not marked as bean, so add @Component or another stereotype annotation to mark it as spring bean.

@Service
public class GameSession extends Thread {
    @Autowired
    private SimpMessagingTemplate template;

    //code here
 }