✨ feat: SSE 기본 기능 구현

Author: LimKangHyun

backend/src/main/java/io/f1/backend/domain/game/sse/SseController.java

@@ -0,0 +1,21 @@
+package io.f1.backend.domain.game.sse;
+
+import java.io.IOException;
+import lombok.RequiredArgsConstructor;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
+import org.springframework.web.servlet.mvc.method.annotation.SseEmitter;
+
+@RestController
+@RequestMapping("/sse")
+@RequiredArgsConstructor
+public class SseController {
+
+    private final SseService sseService;
+
+    @GetMapping("/lobby")
+    public SseEmitter subscribe() {
+        return sseService.subscribe();
+    }
+}

backend/src/main/java/io/f1/backend/domain/game/sse/SseEmitterRepository.java

@@ -0,0 +1,32 @@
+package io.f1.backend.domain.game.sse;
+
+import java.util.List;
+import java.util.concurrent.CopyOnWriteArrayList;
+import org.springframework.stereotype.Repository;
+import org.springframework.web.servlet.mvc.method.annotation.SseEmitter;
+
+@Repository
+public class SseEmitterRepository {
+
+    private final List<SseEmitter> emitters = new CopyOnWriteArrayList<>();
+
+    public void save(SseEmitter emitter) {
+        emitters.add(emitter);
+        // 연결종료 객체정리
+        emitter.onCompletion(() -> {
+            emitters.remove(emitter);
+        });
+        emitter.onTimeout(() -> emitters.remove(emitter));
+        emitter.onError(error -> emitters.remove(emitter));
+    }
+
+    // 연결 종료 객체 정리
+    public void remove(SseEmitter emitter) {
+        emitters.remove(emitter);
+    }
+
+    // 브로드캐스팅
+    public List<SseEmitter> getAll() {
+        return emitters;
+    }
+}

backend/src/main/java/io/f1/backend/domain/game/sse/SseService.java

@@ -0,0 +1,29 @@
+package io.f1.backend.domain.game.sse;
+
+import java.io.IOException;
+import lombok.RequiredArgsConstructor;
+import org.springframework.stereotype.Service;
+import org.springframework.web.servlet.mvc.method.annotation.SseEmitter;
+
+@Service
+@RequiredArgsConstructor
+public class SseService {
+
+    private final SseEmitterRepository emitterRepository;
+
+    public SseEmitter subscribe() {
+        SseEmitter emitter = new SseEmitter(30_000L);
+        emitterRepository.save(emitter);
+
+        try {
+            // emitter 정상 전송확인 메시지
+            emitter.send(SseEmitter.event()
+                .name("connect")
+                .data("connected"));
+        } catch (IOException e) {
+            // emitter send() 호출 시 예외 처리
+            emitterRepository.remove(emitter);
+        }
+        return emitter;
+    }
+}