[DP-518] SSE 하트비트 간헐적으로 안오는 이슈

src/main/java/com/dreamypatisiel/devdevdev/domain/repository/SseEmitterRepository.java

@@ -26,4 +26,8 @@ public SseEmitter findByMemberId(Member member) {
     public Collection<SseEmitter> findAll() {
         return sseEmitters.values();
     }
+
+    public boolean existByMember(Member member) {
+        return sseEmitters.containsKey(member.getId());
+    }
 }

src/main/java/com/dreamypatisiel/devdevdev/domain/service/notification/NotificationService.java

@@ -68,7 +68,6 @@ public SseEmitter createSseEmitter(Long timeout) {
         return new SseEmitter(timeout);
     }
 
-
     /**
      * @param notificationId 알림 ID
      * @param authentication 회원 정보
@@ -264,6 +263,13 @@ private void sendUnreadNotifications(Member findMember, SseEmitter sseEmitter) {
     }
 
     private SseEmitter addClient(Member findMember) {
+        // 구독자 존재 여부 확인
+        boolean isExists = sseEmitterRepository.existByMember(findMember);
+
+        if (isExists) {
+            return sseEmitterRepository.findByMemberId(findMember);
+        }
+
         // 구독자 생성
         SseEmitter sseEmitter = createSseEmitter(TIMEOUT);
         sseEmitterRepository.save(findMember, sseEmitter);

src/test/java/com/dreamypatisiel/devdevdev/domain/service/notification/MockNotificationServiceTest.java

@@ -1,6 +1,7 @@
 package com.dreamypatisiel.devdevdev.domain.service.notification;
 
 import static com.dreamypatisiel.devdevdev.domain.service.notification.NotificationService.UNREAD_NOTIFICATION_FORMAT;
+import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatCode;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.anyLong;
@@ -135,6 +136,29 @@ void addClientAndSendNotificationIoException(Long unreadNotificationCount) throw
         verify(sseEmitterRepository).remove(mockMember);
     }
 
+    @ParameterizedTest
+    @ValueSource(longs = {1, 2, 10, 50, 100})
+    @DisplayName("구독자가 이미 존재하는 경우 기존의 SSEmitter 를 반환합니다.")
+    void addClientAndSendNotificationIsExistMember(Long unreadNotificationCount) throws IOException {
+        // given
+        Authentication mockAuthentication = mock(Authentication.class);
+        Member mockMember = mock(Member.class);
+        SseEmitter realEmitter = new SseEmitter();
+        SseEmitter spyEmitter = spy(realEmitter);
+
+        given(timeProvider.getLocalDateTimeNow()).willReturn(LocalDateTime.of(2025, 1, 1, 0, 0, 0));
+        given(memberProvider.getMemberByAuthentication(mockAuthentication)).willReturn(mockMember);
+        given(sseEmitterRepository.save(mockMember, spyEmitter)).willReturn(spyEmitter);
+        given(sseEmitterRepository.existByMember(mockMember)).willReturn(true);
+        given(sseEmitterRepository.findByMemberId(mockMember)).willReturn(spyEmitter);
+
+        // when
+        SseEmitter sseEmitter = notificationService.addClientAndSendNotification(mockAuthentication);
+
+        // then
+        assertThat(sseEmitter).isEqualTo(spyEmitter);
+    }
+
     @Test
     @DisplayName("구독자에게 알림을 전송합니다.")
     void sendNotification() throws IOException {