spring 向多个客户端广播SseEmitter

sbtkgmzw  于 2023-04-10  发布在  Spring
关注(0)|答案(1)|浏览(342)

我目前正在实现一个通知系统,该系统基于我在阅读有关Spring和SSE的文章时发现的一些示例(以非React式的方式)。
我已经成功地实现了一个解决方案,如果我有一个单一的客户端消费后端发送的事件,它工作得很好。
问题是当我打开几个浏览器并尝试向所有消费者触发事件时:只有订阅SSE广播器端点的最后一个客户端接收该通知。

如何同时向多个客户端触发事件?
如果客户端在同一个网络上,可能只有一个SSE连接是正常的?

下面是我的 * 控制器 *:

@RestController
@RequestMapping("/sse/servlet")
class EventController {
    private val executorService: ScheduledExecutorService = Executors.newSingleThreadScheduledExecutor()
    private val emitters: MutableMap<String, SseEmitter> = mutableMapOf()
    private val objectMapper: ObjectMapper = ObjectMapper()
    private val log = KotlinLogging.logger {}

    @GetMapping("/notifications")
    fun listenNotifications(@RequestParam eventId: String): SseEmitter? {
        if (emitters[eventId] != null) {
            log.info("SSE connection already exists")
            return emitters[eventId]
        }
        val emitter = SseEmitter(TimeUnit.MINUTES.toMillis(10))
        emitter.onCompletion {
            log.info("SSE connection closed")
            emitters.remove(eventId)
        }
        emitter.onTimeout {
            log.info("SSE connection timed out")
            emitter.complete()
        }
        emitter.onError { throwable: Throwable? ->
            log.error("Listen SSE exception", throwable)
        }
        emitters[eventId] = emitter
        return emitter
    }

    @PostMapping("/notifications")
    @ResponseStatus(ACCEPTED)
    fun fireNotification(
        @RequestParam eventId: String,
        @RequestBody notification: Notification
    ) {
        val sseEmitter = emitters[eventId]
        if (sseEmitter === null) {
            log.info("SSE connection does not exist")
            return
        }
        handleEmitter(notification, sseEmitter, eventId)
    }

    private fun handleEmitter(
        notification: Notification,
        sseEmitter: SseEmitter,
        eventId: String
    ) = try {
        val data = objectMapper.writeValueAsString(notification)
        val sseEventBuilder = event().data(data)
        sseEmitter.send(sseEventBuilder)
    } catch (ioException: IOException) {
        log.error("Send SSE exception", ioException)
        emitters.remove(eventId)
    }

通知模型

data class Notification(val message: String)

我非常简单的 application.yaml 属性文件

server:
  servlet:
    context-path: /api

我的 gradle 配置

import org.jetbrains.kotlin.gradle.tasks.KotlinCompile

plugins {
    id("org.springframework.boot") version "3.0.4"
    id("io.spring.dependency-management") version "1.1.0"
    kotlin("jvm") version "1.7.22"
    kotlin("plugin.spring") version "1.7.22"
}

group = "com.ggardet"
version = "0.0.1-SNAPSHOT"
java.sourceCompatibility = JavaVersion.VERSION_17

repositories {
    mavenCentral()
}

dependencies {
    implementation("com.fasterxml.jackson.module:jackson-module-kotlin")
    implementation("io.github.microutils:kotlin-logging-jvm:2.0.11")
    implementation("org.jetbrains.kotlin:kotlin-reflect")
    implementation("org.springframework.boot:spring-boot-starter-web")
    implementation("org.springframework.boot:spring-boot-starter-security")
}

tasks.withType<KotlinCompile> {
    kotlinOptions {
        freeCompilerArgs = listOf("-Xjsr305=strict")
        jvmTarget = "17"
    }
}

最后是用于创建/使用事件的请求(使用httpie)

# to listen for events I open 2 or 3 terminals and launch the following request
http --stream -a user:user -v GET http://localhost:8080/api/sse/servlet/notifications\?eventId\=1
# to fire a new event I open another terminal instance and launch this single request
http -a user:user -v POST http://localhost:8080/api/sse/servlet/notifications\?eventId\=1 message=test

x1c 0d1x感谢任何形式的帮助

  • 注意:如果我删除“emitters”map并在类级别使用单个SseEmitter发送事件,我会遇到同样的问题。
nzkunb0c

nzkunb0c1#

所以我没有意识到客户端不能共享同一个SseEmitter。
我不得不创建一个SseEmitter每个订阅使其工作。
回答问题:

  • 每次新客户端订阅 */notification * 端点时,我都必须存储一个新的SseEmitter,而不是将同一个SeeEmitter共享给所有订阅者
  • 不需要,客户端不需要在不同的网络上即可订阅 */notification * 端点

不确定这是否是最好的方法,但我在这里发布我的解决方案,以防有人误解SseEmitter的工作原理,就像我做的一样:

@RestController
@RequestMapping("/sse/servlet")
class EventController {
    private val executorService: ScheduledExecutorService = Executors.newSingleThreadScheduledExecutor()
    private val emitters = ConcurrentHashMap<String, CopyOnWriteArrayList<SseEmitter>>()
    private val objectMapper: ObjectMapper = ObjectMapper()
    private val log = KotlinLogging.logger {}

    @GetMapping("/notifications", produces = [MediaType.TEXT_EVENT_STREAM_VALUE])
    fun listenNotifications(@RequestParam eventId: String): SseEmitter? {
        val emitter = SseEmitter(Duration.ofMinutes(10).toMillis())
        emitter.onCompletion {
            log.info("SSE connection closed")
            emitters.remove(eventId)
        }
        emitter.onTimeout {
            log.info("SSE connection timed out")
            emitters.remove(eventId)
            emitter.complete()
        }
        emitter.onError { throwable: Throwable? ->
            log.error("Listen SSE exception", throwable)
            emitters.remove(eventId)
        }
        emitters.computeIfAbsent(eventId) { CopyOnWriteArrayList() }.add(emitter)
        return emitter
    }

    @PostMapping("/notifications")
    @ResponseStatus(ACCEPTED)
    fun fireNotification(
        @RequestParam eventId: String,
        @RequestBody notification: Notification
    ) = emitters[eventId]?.forEach { handleEmitter(notification, it) }

    private fun handleEmitter(
        notification: Notification,
        sseEmitter: SseEmitter,
    ) = try {
        val data = objectMapper.writeValueAsString(notification)
        val sseEventBuilder = event().data(data)
        sseEmitter.send(sseEventBuilder)
    } catch (ioException: IOException) {
        log.error("Send SSE exception", ioException)
    }
}

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