@RestController
@RequestMapping("/api/sse")
public class SseController {

    // 用于存儲(chǔ)已連接的客戶端，實(shí)際生產(chǎn)中建議使用專門的服務(wù)類管理
    private static final Map<String, SseEmitter> emitters = new ConcurrentHashMap<>();

    @GetMapping(value = "/subscribe/{userId}", produces = MediaType.TEXT_EVENT_STREAM_VALUE)
    public SseEmitter subscribe(@PathVariable String userId) {
        // 設(shè)置超時(shí)時(shí)間（單位毫秒），0 表示永不超時(shí)
        SseEmitter emitter = new SseEmitter(60_000L); 

        emitters.put(userId, emitter);

        // 注冊(cè)回調(diào)
        emitter.onCompletion(() -> emitters.remove(userId));
        emitter.onTimeout(() -> emitters.remove(userId));
        emitter.onError((e) -> emitters.remove(userId));

        // 建立連接后立即發(fā)送一條消息，防止某些代理或?yàn)g覽器認(rèn)為連接已失效
        try {
            emitter.send(SseEmitter.event().name("INIT").data("Connected!"));
        } catch (IOException e) {
            emitter.completeWithError(e);
        }

        return emitter;
    }
}

public void sendMessage(String userId, String content) {
    SseEmitter emitter = emitters.get(userId);
    if (emitter != null) {
        try {
            // 可以發(fā)送純文本，也可以發(fā)送封裝好的對(duì)象（會(huì)自動(dòng)轉(zhuǎn) JSON）
            emitter.send(SseEmitter.event()
                    .id(UUID.randomUUID().toString())
                    .name("message") // 對(duì)應(yīng)前端的事件名
                    .data(content)
                    .reconnectTime(3000)); // 提示客戶端重連間隔
        } catch (IOException e) {
            emitters.remove(userId);
            emitter.completeWithError(e);
        }
    }
}

const eventSource = new EventSource('/api/sse/subscribe/user123');

eventSource.onmessage = (event) => {
    console.log("收到通用消息:", event.data);
};

// 監(jiān)聽特定類型的事件 (對(duì)應(yīng)后端的 .name("message"))
eventSource.addEventListener('message', (event) => {
    const data = JSON.parse(event.data);
    console.log("處理后的數(shù)據(jù):", data);
});

eventSource.onerror = (error) => {
    console.error("SSE 錯(cuò)誤:", error);
    eventSource.close();
};