Kotlin 使用 Spring WebFlux 实现响应式编程
IBM的研究称，整个人类文明所获得的全部数据中，有90%是过去两年内产生的。在此背景下，包括NoSQL，Hadoop, Spark, Storm, Kylin在内的大批新技术应运而生。其中以RxJava和Reactor为代表的响应式（Reactive）编程技术针对的就是经典的大数据
4V定义: Volume，Variety，Velocity，Value）
中的Velocity，即高并发问题，而在即将发布的Spring 5中，也引入了响应式编程的支持。在接下来的博客文章中，我会围绕响应式编程相关的主题与你分享我的学习心得。作为第一篇，首先从Spring 5 和 Spring WebFlux 谈起。
响应式宣言
响应式宣言和敏捷宣言一样，说起响应式编程，必先提到响应式宣言。
We want systems that are Responsive, Resilient, Elastic and Message Driven. We call these Reactive Systems. - The Reactive Manifesto
响应式宣言中也包含了4组关键词：
Responsive: 可响应的。要求系统尽可能做到在任何时候都能及时响应。
Resilient: 可恢复的。要求系统即使出错了，也能保持可响应性。
Elastic: 可伸缩的。要求系统在各种负载下都能保持可响应性。
Message Driven: 消息驱动的。要求系统通过异步消息连接各个组件。
可以看到，对于任何一个响应式系统，首先要保证的就是可响应性，否则就称不上是响应式系统。从这个意义上来说，动不动就蓝屏的Windows系统显然不是一个响应式系统。
Spring 5 响应式Web框架架构图
左侧是传统的基于Servlet的Spring Web MVC框架
右侧是5.0版本新引入的基于Reactive Streams的Spring WebFlux框架
从上到下依次是
Router Functions
WebFlux
Reactive Streams
三个新组件。
Router Functions:
对标@Controller，@RequestMapping等标准的Spring MVC注解，提供一套函数式风格的API，用于创建Router，Handler和Filter。
WebFlux: 核心组件
协调上下游各个组件提供响应式编程支持。
Reactive Streams
一种支持背压（Backpressure）的异步数据流处理标准，主流实现有RxJava和Reactor，Spring WebFlux默认集成的是Reactor。
在Web容器的选择上，Spring WebFlux既支持像Tomcat，Jetty这样的的传统容器（前提是支持Servlet 3.1 Non-Blocking IO API），又支持像Netty，Undertow那样的异步容器。不管是何种容器，Spring WebFlux都会将其输入输出流适配成Flux<DataBuffer>格式，以便进行统一处理。
值得一提的是，除了新的Router Functions接口，Spring WebFlux同时支持使用老的Spring MVC注解声明Reactive Controller。和传统的MVC Controller不同，Reactive Controller操作的是非阻塞的ServerHttpRequest和ServerHttpResponse，而不再是Spring MVC里的HttpServletRequest和HttpServletResponse。
下面是示例工程详解。
示例工程详解
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工程目录结构
~/ak47/webflux$ tree . ├── build.gradle ├── gradle │ └── wrapper │ ├── gradle-wrapper.jar │ └── gradle-wrapper.properties ├── gradlew ├── gradlew.bat ├── src │ ├── main │ │ ├── java │ │ ├── kotlin │ │ │ └── com │ │ │ └── easy │ │ │ └── kotlin │ │ │ └── webflux │ │ │ └── WebfluxApplication.kt │ │ └── resources │ │ └── application.properties │ └── test │ ├── java │ ├── kotlin │ │ └── com │ │ └── easy │ │ └── kotlin │ │ └── webflux │ │ └── WebfluxApplicationTests.kt │ └── resources └── webflux.iml19 directories, 11 files
项目依赖配置
buildscript {
ext {
kotlinVersion = '1.1.51'
springBootVersion = '2.0.0.BUILD-SNAPSHOT'
}
repositories {
mavenCentral()
maven { url "https://repo.spring.io/snapshot" }
maven { url "https://repo.spring.io/milestone" }
}
dependencies {
classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")
classpath("org.jetbrains.kotlin:kotlin-gradle-plugin:${kotlinVersion}")
classpath("org.jetbrains.kotlin:kotlin-allopen:${kotlinVersion}")
}
}
apply plugin: 'kotlin'apply plugin: 'kotlin-spring'apply plugin: 'eclipse'apply plugin: 'org.springframework.boot'apply plugin: 'io.spring.dependency-management'group = 'com.easy.kotlin'version = '0.0.1-SNAPSHOT'sourceCompatibility = 1.8compileKotlin {
kotlinOptions.jvmTarget = "1.8"}
compileTestKotlin {
kotlinOptions.jvmTarget = "1.8"}
repositories {
mavenCentral()
maven { url "https://repo.spring.io/snapshot" }
maven { url "https://repo.spring.io/milestone" }
}
dependencies {
compile('org.springframework.boot:spring-boot-starter-webflux')
compile("org.jetbrains.kotlin:kotlin-stdlib-jre8")
compile("org.jetbrains.kotlin:kotlin-reflect")
testCompile('org.springframework.boot:spring-boot-starter-test')
testCompile('io.projectreactor:reactor-test')
}这是 Spring Initializr 帮我们自动生成的样板工程。下面我们分别来加入 Model 、dao 、 service 、 handler 等模块的内容。
源码目录结构设计如下
├── src│ ├── main│ │ ├── java│ │ ├── kotlin│ │ │ └── com│ │ │ └── easy│ │ │ └── kotlin│ │ │ └── webflux│ │ │ ├── WebfluxApplication.kt│ │ │ ├── dao│ │ │ │ └── PersonRepository.kt│ │ │ ├── handler│ │ │ │ └── PersonHandler.kt│ │ │ ├── model│ │ │ │ └── Person.kt│ │ │ ├── router│ │ │ │ └── RouterConfig.kt│ │ │ ├── server│ │ │ │ └── HttpServerConfig.kt│ │ │ └── service│ │ │ └── PersonService.kt│ │ └── resources│ │ └── application.properties
Person
package com.easy.kotlin.webflux.modelimport com.fasterxml.jackson.annotation.JsonPropertyclass Person(@JsonProperty("name") val name: String, @JsonProperty("age") val age: Int) { override fun toString(): String { return "Person{" + "name='" + name + '\'' + ", age=" + age + '}'
}
}PersonRepository
package com.easy.kotlin.webflux.daoimport com.easy.kotlin.webflux.model.Personimport reactor.core.publisher.Fluximport reactor.core.publisher.Monointerface PersonRepository { fun getPerson(id: Int): Mono<Person> fun allPeople(): Flux<Person> fun savePerson(person: Mono<Person>): Mono<Void>
}/*
* Mono 和 Flux 是由 Project Reactor 提供的 Reactive 类型。
* Springs 同时支持其他 Reactive 流实现，如 RXJava。
* Mono 和 Flux 是由 Reactive 流的 Publisher 中实现的。
* Mono 是一个用来发送 0 或者单值数据的发布器，
* Flux 可以用来发送 0 到 N 个值。
*
* 这非常类似 Flowable 和 RxJava 中的 Observable 。它们表示在订阅这些发布服务时发送数值流。 */PersonService
package com.easy.kotlin.webflux.serviceimport com.easy.kotlin.webflux.model.Personimport com.easy.kotlin.webflux.dao.PersonRepositoryimport org.springframework.stereotype.Serviceimport reactor.core.publisher.Fluximport reactor.core.publisher.Mono@Serviceclass PersonService : PersonRepository {
var persons: MutableMap<Int, Person> = hashMapOf() constructor() { this.persons[1] = Person("Jack", 20) this.persons[2] = Person("Rose", 16)
} override fun getPerson(id: Int): Mono<Person> { return Mono.justOrEmpty(this.persons[id])
} override fun allPeople(): Flux<Person> { return Flux.fromIterable(this.persons.values)
} override fun savePerson(person: Mono<Person>): Mono<Void> { return person.doOnNext { val id = this.persons.size + 1
persons.put(id, it)
println("Saved ${person} with ${id}")
}.thenEmpty(Mono.empty())
}
}PersonHandler
package com.easy.kotlin.webflux.handlerimport com.easy.kotlin.webflux.dao.PersonRepositoryimport com.easy.kotlin.webflux.model.Personimport org.springframework.beans.factory.annotation.Autowiredimport reactor.core.publisher.Monoimport org.springframework.web.reactive.function.server.ServerRequestimport org.springframework.web.reactive.function.server.ServerResponseimport org.springframework.http.MediaType.APPLICATION_JSONimport org.springframework.stereotype.Serviceimport org.springframework.web.reactive.function.BodyInserters.fromObject@Serviceclass PersonHandler { @Autowired lateinit var repository: PersonRepository fun getPerson(request: ServerRequest): Mono<ServerResponse> { val personId = Integer.valueOf(request.pathVariable("id"))!! val notFound = ServerResponse.notFound().build() val personMono = this.repository.getPerson(personId) return personMono
.flatMap { person -> ServerResponse.ok().contentType(APPLICATION_JSON).body(fromObject(person)) }
.switchIfEmpty(notFound)
} fun createPerson(request: ServerRequest): Mono<ServerResponse> { val person = request.bodyToMono(Person::class.java)
return ServerResponse.ok().build(this.repository.savePerson(person))
} fun listPeople(request: ServerRequest): Mono<ServerResponse> { val people = this.repository.allPeople() return ServerResponse.ok().contentType(APPLICATION_JSON).body(people, Person::class.java)
}
}RouterConfig
package com.easy.kotlin.webflux.routerimport com.easy.kotlin.webflux.handler.PersonHandlerimport org.springframework.beans.factory.annotation.Autowiredimport org.springframework.context.annotation.Beanimport org.springframework.context.annotation.Configurationimport org.springframework.http.MediaType.APPLICATION_JSONimport org.springframework.web.reactive.function.server.HandlerFunctionimport org.springframework.web.reactive.function.server.RequestPredicates.GETimport org.springframework.web.reactive.function.server.RequestPredicates.acceptimport org.springframework.web.reactive.function.server.RouterFunctionimport org.springframework.web.reactive.function.server.RouterFunctions.route@Configurationclass RouterConfig { @Autowired lateinit var personHandler: PersonHandler @Bean
fun routerFunction(): RouterFunction<*> { return route(GET("/api/person").and(accept(APPLICATION_JSON)),
HandlerFunction { personHandler.listPeople(it) })
.and(route(GET("/api/person/{id}").and(accept(APPLICATION_JSON)),
HandlerFunction { personHandler.getPerson(it) }))
}
}HttpServerConfig
package com.easy.kotlin.webflux.serverimport org.springframework.beans.factory.annotation.Autowiredimport org.springframework.context.annotation.Beanimport org.springframework.context.annotation.Configurationimport org.springframework.core.env.Environmentimport org.springframework.http.server.reactive.ReactorHttpHandlerAdapterimport org.springframework.web.reactive.function.server.RouterFunctionimport org.springframework.web.reactive.function.server.RouterFunctionsimport reactor.ipc.netty.http.server.HttpServer@Configurationclass HttpServerConfig { @Autowired
lateinit var environment: Environment @Bean
fun httpServer(routerFunction: RouterFunction<*>): HttpServer { val httpHandler = RouterFunctions.toHttpHandler(routerFunction) val adapter = ReactorHttpHandlerAdapter(httpHandler) val server = HttpServer.create("localhost", environment.getProperty("server.port").toInt())
server.newHandler(adapter) return server
}
}项目启动入口类 WebfluxApplication
package com.easy.kotlin.webfluximport org.springframework.boot.autoconfigure.SpringBootApplicationimport org.springframework.boot.runApplication@SpringBootApplicationclass WebfluxApplicationfun main(args: Array<String>) {
runApplication<WebfluxApplication>(*args)
}启动运行
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注意到这行：
Mapped ((GET && /api/person) && Accept: [application/json]) -> com.easy.kotlin.webflux.router.RouterConfig$routerFunction$1@46292372
((GET && /api/person/{id}) && Accept: [application/json]) -> com.easy.kotlin.webflux.router.RouterConfig$routerFunction$2@126be319完整启动日志
. ____ _ __ _ _
/\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\\/ ___)| |_)| | | | | || (_| | ) ) ) )
' |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot :: (v2.0.0.BUILD-SNAPSHOT)
2017-11-04 00:39:46.046 INFO 2884 --- [ main] c.e.kotlin.webflux.WebfluxApplicationKt : Starting WebfluxApplicationKt on jacks-MacBook-Air.local with PID 2884 (/Users/jack/ak47/webflux/out/production/classes started by jack in /Users/jack/ak47/webflux)
2017-11-04 00:39:46.077 INFO 2884 --- [ main] c.e.kotlin.webflux.WebfluxApplicationKt : No active profile set, falling back to default profiles: default
2017-11-04 00:39:46.247 INFO 2884 --- [ main] .r.c.ReactiveWebServerApplicationContext : Refreshing org.springframework.boot.web.reactive.context.ReactiveWebServerApplicationContext@4b0b0854: startup date [Sat Nov 04 00:39:46 CST 2017]; root of context hierarchy
2017-11-04 00:39:48.995 INFO 2884 --- [ main] o.s.w.r.f.s.s.RouterFunctionMapping : Mapped ((GET && /api/person) && Accept: [application/json]) -> com.easy.kotlin.webflux.router.RouterConfig$routerFunction$1@46292372
((GET && /api/person/{id}) && Accept: [application/json]) -> com.easy.kotlin.webflux.router.RouterConfig$routerFunction$2@126be319
2017-11-04 00:39:49.017 INFO 2884 --- [ main] o.s.w.r.handler.SimpleUrlHandlerMapping : Mapped URL path [/webjars/**] onto handler of type [class org.springframework.web.reactive.resource.ResourceWebHandler]
2017-11-04 00:39:49.017 INFO 2884 --- [ main] o.s.w.r.handler.SimpleUrlHandlerMapping : Mapped URL path [/**] onto handler of type [class org.springframework.web.reactive.resource.ResourceWebHandler]
2017-11-04 00:39:49.215 INFO 2884 --- [ main] o.s.w.r.r.m.a.ControllerMethodResolver : Looking for @ControllerAdvice: org.springframework.boot.web.reactive.context.ReactiveWebServerApplicationContext@4b0b0854: startup date [Sat Nov 04 00:39:46 CST 2017]; root of context hierarchy
2017-11-04 00:39:50.309 INFO 2884 --- [ main] o.s.j.e.a.AnnotationMBeanExporter : Registering beans for JMX exposure on startup
2017-11-04 00:39:50.459 INFO 2884 --- [ctor-http-nio-1] r.ipc.netty.tcp.BlockingNettyContext : Started HttpServer on /0:0:0:0:0:0:0:0:9000
2017-11-04 00:39:50.459 INFO 2884 --- [ main] o.s.b.web.embedded.netty.NettyWebServer : Netty started on port(s): 9000
2017-11-04 00:39:50.466 INFO 2884 --- [ main] c.e.kotlin.webflux.WebfluxApplicationKt : Started WebfluxApplicationKt in 5.047 seconds (JVM running for 6.276)测试输出
$ curl http://127.0.0.1:9000/api/person
[{"name":"Jack","age":20},{"name":"Rose","age":16}]
$ curl http://127.0.0.1:9000/api/person/1{"name":"Jack","age":20}
$ curl http://127.0.0.1:9000/api/person/2{"name":"Rose","age":16}小结
Spring Web 是一个命令式的编程框架，可以很方便的进行开发和调试。你需要根据实际情况去决定采用 Spring 5 Reactive 或者是 Spring Web 命令式框架。在很多情况下，命令式的编程风格就可以满足，但当你的应用需要高可伸缩性，那么 Reactive 非堵塞方式是最适合的。
本章工程源代码：https://github.com/EasyKotlin/kotlin-with-webflux
作者：一个会写诗的程序员
链接：https://www.jianshu.com/p/47262af24c54