Spring Boot SSE实战：SseEmitter实现多客户端事件广播与心跳保活

1. 添加依赖 (pom.xml)

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
</dependencies>

2. 事件服务 (EventService.java)

import org.springframework.stereotype.Service;
import org.springframework.web.servlet.mvc.method.annotation.SseEmitter;

import java.io.IOException;
import java.util.Map;
import java.util.UUID;
import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicInteger;

@Service
public class EventService {
    // 线程安全的Emitter存储
    private final ConcurrentMap<String, SseEmitter> emitters = new ConcurrentHashMap<>();
    // 心跳调度器
    private final ScheduledExecutorService heartbeatExecutor = Executors.newSingleThreadScheduledExecutor();
    // 事件计数器
    private final AtomicInteger eventCounter = new AtomicInteger(0);

    public EventService() {
        // 启动心跳任务 (每25秒发送一次)
        heartbeatExecutor.scheduleAtFixedRate(this::broadcastHeartbeat, 0, 25, TimeUnit.SECONDS);
    }

    // 客户端订阅
    public SseEmitter subscribe() {
        String clientId = UUID.randomUUID().toString();
        SseEmitter emitter = new SseEmitter(60_000L); // 1分钟超时
        
        // 注册事件处理器
        emitter.onCompletion(() -> removeEmitter(clientId));
        emitter.onTimeout(() -> {
            removeEmitter(clientId);
            emitter.complete();
        });
        emitter.onError(ex -> removeEmitter(clientId));
        
        emitters.put(clientId, emitter);
        return emitter;
    }

    // 广播事件
    public void broadcast(String eventName, Object data) {
        emitters.forEach((clientId, emitter) -> {
            try {
                emitter.send(SseEmitter.event()
                    .id(String.valueOf(eventCounter.incrementAndGet()))
                    .name(eventName)
                    .data(data)
                );
            } catch (IOException | IllegalStateException e) {
                removeEmitter(clientId); // 发送失败则移除
            }
        });
    }

    // 广播心跳
    private void broadcastHeartbeat() {
        emitters.forEach((clientId, emitter) -> {
            try {
                emitter.send(SseEmitter.event()
                    .comment("heartbeat") // 发送注释类型的心跳
                );
            } catch (Exception ignored) {
                // 心跳失败不移除，等待超时机制处理
            }
        });
    }

    // 移除客户端
    private void removeEmitter(String clientId) {
        SseEmitter emitter = emitters.remove(clientId);
        if (emitter != null) {
            emitter.complete();
        }
    }

    // 关闭服务 (资源清理)
    public void shutdown() {
        // 1. 停止心跳线程
        heartbeatExecutor.shutdownNow();
        
        // 2. 关闭所有连接
        emitters.forEach((id, emitter) -> {
            try {
                emitter.send(SseEmitter.event()
                    .name("system")
                    .data(Map.of("action", "shutdown"))
                );
            } catch (Exception ignored) {
            } finally {
                emitter.complete();
            }
        });
        
        // 3. 清空集合
        emitters.clear();
    }
}

3. 控制器 (EventController.java)

import org.springframework.http.MediaType;
import org.springframework.web.bind.annotation.*;
import org.springframework.web.servlet.mvc.method.annotation.SseEmitter;

@RestController
@RequestMapping("/events")
public class EventController {
    private final EventService eventService;

    public EventController(EventService eventService) {
        this.eventService = eventService;
    }

    // 客户端订阅入口
    @GetMapping(produces = MediaType.TEXT_EVENT_STREAM_VALUE)
    public SseEmitter subscribe() {
        return eventService.subscribe();
    }

    // 广播消息入口(这里是模拟消息推送过来，会把该条消息都放入到已订阅的客户端)
    @PostMapping("/broadcast")
    public void broadcast(@RequestParam String message) {
        eventService.broadcast("message", Map.of(
            "content", message,
            "timestamp", System.currentTimeMillis()
        ));
    }
}

4. 应用配置 (Application.java)

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;

@SpringBootApplication
public class SseApplication {
    public static void main(String[] args) {
        ApplicationContext context = SpringApplication.run(SseApplication.class, args);
        
        // 注册优雅关闭钩子
        Runtime.getRuntime().addShutdownHook(new Thread(() -> {
            EventService eventService = context.getBean(EventService.class);
            eventService.shutdown();
            System.out.println("SSE资源已清理完成");
        }));
    }
}

5. 客户端示例 (JavaScript)

<!DOCTYPE html>
<html>
<body>
    <h1>SSE客户端</h1>
    <div id="messages"></div>

    <script>
        const messageContainer = document.getElementById('messages');
        let eventSource;
        
        function connect() {
            eventSource = new EventSource('http://localhost:8080/events');
            
            eventSource.addEventListener('message', (e) => {
                const data = JSON.parse(e.data);
                addMessage(`消息: ${data.content} [${new Date(data.timestamp).toLocaleTimeString()}]`);
            });
            
            eventSource.addEventListener('system', (e) => {
                const data = JSON.parse(e.data);
                if (data.action === 'shutdown') {
                    addMessage('系统通知: 服务即将关闭');
                    eventSource.close();
                }
            });
            
            eventSource.onerror = (e) => {
                addMessage('连接错误，3秒后重连...');
                setTimeout(connect, 3000);
            };
        }
        
        function addMessage(text) {
            const p = document.createElement('p');
            p.textContent = text;
            messageContainer.appendChild(p);
            messageContainer.scrollTop = messageContainer.scrollHeight;
        }
        
        // 初始连接
        connect();
    </script>
</body>
</html>

关键机制说明

1. 心跳机制：

   • 每25秒发送一次空注释事件 :heartbeat

   • 防止代理或负载均衡器关闭空闲连接

   • 客户端可通过监听所有事件检测心跳

2. 关闭流程：

   

3. 客户端重连：

   • 使用事件ID支持断线续传

   • 客户端错误时自动重连

   • 服务端关闭时发送系统通知