const eventSource = new EventSource("/sse/subscribe");
eventSource.onmessage = function(event) {
    console.log("收到消息:", event.data);
};
eventSource.onerror = function(e) {
    console.error("連接錯(cuò)誤", e);
};

<!-- Maven 中無需額外添加，spring-boot-starter-web 已包含 -->

@RestController
public class SseController {
    @GetMapping("/sse/subscribe")
    public SseEmitter subscribe() {
        SseEmitter emitter = new SseEmitter(0L); // 不超時(shí)，或設(shè)置時(shí)間，如30_000L
        Executors.newSingleThreadExecutor().submit(() -> {
            try {
                for (int i = 1; i <= 5; i++) {
                    emitter.send("第 " + i + " 條消息");
                    Thread.sleep(1000);
                }
                emitter.complete(); // 關(guān)閉連接
            } catch (Exception e) {
                emitter.completeWithError(e);
            }
        });
        return emitter;
    }
}

Content-Type: text/event-stream

@GetMapping(value = "/sse/subscribe", produces = MediaType.TEXT_EVENT_STREAM_VALUE)

private final Map<String, SseEmitter> userEmitters = new ConcurrentHashMap<>();
@GetMapping("/subscribe/{userId}")
public SseEmitter subscribe(@PathVariable String userId) {
    SseEmitter emitter = new SseEmitter(60_000L);
    userEmitters.put(userId, emitter);
    emitter.onCompletion(() -> userEmitters.remove(userId));
    emitter.onTimeout(() -> userEmitters.remove(userId));
    return emitter;
}
public void sendToUser(String userId, String message) throws IOException {
    SseEmitter emitter = userEmitters.get(userId);
    if (emitter != null) {
        emitter.send(message);
    }
}

emitter.send(SseEmitter.event()
    .name("customEvent")
    .data("這是自定義事件")
);

eventSource.addEventListener("customEvent", function(event) {
    console.log("收到自定義事件:", event.data);
});

ScheduledExecutorService heartbeatScheduler = Executors.newScheduledThreadPool(1);
heartbeatScheduler.scheduleAtFixedRate(() -> {
    try {
        emitter.send("heartbeat");
    } catch (IOException e) {
        emitter.completeWithError(e);
    }
}, 0, 15, TimeUnit.SECONDS);