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使用 Kotlin + WebFlux/RxJava 2 实现响应式以及尝试正式版本的协程

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SpringBoot Kotlin

在前一篇文章《使用 Kotlin + Spring Boot 进行后端开发》中，曾介绍过尝试使用 Kotlin 来做后端开发。这一次，尝试 WebFlux 以及协程。

首先，在build.gradle中添加插件和依赖的库。

plugins {
    id 'java'
    id 'org.jetbrains.kotlin.jvm' version '1.3.10'
    id "org.jetbrains.kotlin.plugin.allopen" version "1.3.10"
}

ext {
    libraries = [

            rxjava                    : "2.2.2",

            logback                   : "1.2.3",

            spring_boot               : "2.1.0.RELEASE",

            kotlinx_coroutines_core   : "1.0.1"
    ]
}

group 'com.kotlin.tutorial'
version '1.0-SNAPSHOT'

sourceCompatibility = 1.8

def libs = rootProject.ext.libraries // 库

repositories {
    mavenCentral()
}

dependencies {
    compile "org.jetbrains.kotlin:kotlin-stdlib-jdk8"
    compile "org.jetbrains.kotlin:kotlin-reflect:1.3.10"
    testCompile group: 'junit', name: 'junit', version: '4.12'

    implementation "io.reactivex.rxjava2:rxjava:${libs.rxjava}"

    implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core:${libs.kotlinx_coroutines_core}"
    implementation "org.jetbrains.kotlinx:kotlinx-coroutines-rx2:${libs.kotlinx_coroutines_core}"

    implementation "ch.qos.logback:logback-classic:${libs.logback}"
    implementation "ch.qos.logback:logback-core:${libs.logback}"
    implementation "ch.qos.logback:logback-access:${libs.logback}"

    implementation "org.springframework.boot:spring-boot-starter-web:${libs.spring_boot}"
    implementation "org.springframework.boot:spring-boot-starter-data-mongodb-reactive:${libs.spring_boot}"
}

compileKotlin {
    kotlinOptions.jvmTarget = "1.8"
}
compileTestKotlin {
    kotlinOptions.jvmTarget = "1.8"
}

此次，使用了 allopen 插件。它是官方提供的插件详见：https://kotlinlang.org/docs/reference/compiler-plugins.html

Kotlin 的类默认是final的，一般需要使用open关键字。使用了allopen插件就可以节省open关键字。值得注意的是，需要打开 Intellij 的 Enable annotation processing 选项。

这样，创建 SpringKotlinApplication 就不需要使用open：

import org.springframework.boot.SpringApplication
import org.springframework.boot.autoconfigure.SpringBootApplication


/**
 * Created by tony on 2018/11/13.
 */
@SpringBootApplication
class SpringKotlinApplication

fun main(args: Array<String>) {
    SpringApplication.run(SpringKotlinApplication::class.java, *args)
}

另外，不要忘记配置数据库的信息，例子采用的是 MongoDB。

WebFlux

WebFlux 是 Spring 5 新增的特性，相对于传统 MVC 的同步阻塞IO模型，它采用异步非阻塞的IO模型。

WebFlux 的 Flux 取自于 Reactor 中的类 Flux。Reactor 是 Spring 5 响应式开发的基础。

Reactor 是完全基于响应式流规范设计和实现的库，Flux 和 Mono 是 Reactor 中的两个基本概念。

Flux 类似 RxJava 的 Observable，它可以触发零到多个事件，并根据实际情况结束处理或触发错误。Mono 最多只触发一个事件，它跟 RxJava 的 Single 和 Maybe 类似，所以可以把 Mono 用于在异步任务完成时发出通知。

1.1 创建 Model

首先，创建几个 Model 类。

User 表示用户对象。

import org.springframework.data.annotation.Id

/**
 * Created by tony on 2018/11/22.
 */
data class User(@Id val id: String? = null, val name: String, val age: Int, val address: Address) {

    constructor() : this(null, "", 0, Address())
    constructor(name: String, age: Int, address: Address) : this(null, name = name, age = age, address = address)
}

Address 记录用户的地址。

import org.springframework.data.annotation.Id

/**
 * Created by tony on 2018/11/22.
 */
data class Address(@Id val id: String? = null, val number: Int, val street: String, val city: String) {

    constructor() : this(null, 0, "", "")
    constructor(number: Int, street: String, city: String) : this(null, number, street, city)
}

Audit 用于记录用户操作的时间。


import org.springframework.data.annotation.Id
import java.time.LocalDateTime

/**
 * Created by tony on 2018/11/22.
 */
data class Audit(@Id val id: String? = null, val name: String, val eventDate: LocalDateTime) {

    constructor() : this(null, "",LocalDateTime.now())

    constructor(name: String, eventDate: LocalDateTime) : this(null, name, eventDate)
}

1.2 创建 Repository

创建 UserReactiveRepository 用于 User 对象的查询操作，它实现 ReactiveMongoRepository 接口。

import com.kotlin.tutorial.model.User
import org.springframework.data.mongodb.repository.ReactiveMongoRepository
import org.springframework.stereotype.Repository
import reactor.core.publisher.Flux

/**
 * Created by tony on 2018/11/22.
 */
@Repository
interface UserReactiveRepository : ReactiveMongoRepository<User, String> {

    fun findUserByAge(age: Int): Flux<User>

    fun findUserByAddressCity(city: String): Flux<User>

    fun findUserByAgeAndAddressCity(age: Int, city: String): Flux<User>
}

创建 AuditRepository 用于查询用户最近一条的操作时间。

import com.kotlin.tutorial.model.Audit
import org.springframework.data.repository.CrudRepository
import org.springframework.stereotype.Repository

/**
 * Created by tony on 2018/11/22.
 */
@Repository
interface AuditRepository: CrudRepository<Audit, String> {

    fun findFirstByNameOrderByEventDateDesc(name: String): Audit
}

1.3 创建 Service

创建 UserReactiveService，通过依赖注入了 userRepository、auditRepository。

import com.kotlin.tutorial.Utils.toLower
import com.kotlin.tutorial.model.Address
import com.kotlin.tutorial.model.Audit
import com.kotlin.tutorial.model.User
import com.kotlin.tutorial.repository.AuditRepository
import com.kotlin.tutorial.repository.UserReactiveRepository
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.stereotype.Component
import reactor.core.publisher.Flux
import java.time.LocalDateTime

/**
 * Created by tony on 2018/11/22.
 */
@Component
class UserReactiveService {

    @Autowired
    lateinit var userRepository: UserReactiveRepository

    @Autowired
    lateinit var auditRepository: AuditRepository

    companion object {

        val cities = listOf("Shanghai", "Suzhou", "Hangzhou").toLower()
        val streets = listOf("renming road", "zhongshan road").toLower()
    }

    fun find(age: Int?, rawCity: String?): Flux<User> {
        val city = rawCity?.toLowerCase()

        return when {

            age is Int && city is String -> userRepository.findUserByAgeAndAddressCity(age, city)

            city is String -> userRepository.findUserByAddressCity(city)

            age is Int -> userRepository.findUserByAge(age)

            else -> userRepository.findAll()
        }
    }

    fun generateData(): Flux<User> {

        val list = listOf(20, 25, 33, 28, 34).map {

            val u = generate(it)

            auditRepository.save(Audit(u.name, LocalDateTime.now()))

            u
        }

        return userRepository.deleteAll().thenMany(userRepository.saveAll(list))
    }

    private fun generate(age: Int): User {

        val address = Address(age, streets[age % streets.size], cities[age % cities.size])
        return User("Tony$age", age, address)
    }
}

1.4 创建 Controller

创建 UserController 编写两个 reactive 的接口：

@RestController
@RequestMapping("/user")
class UserController {

    @Autowired
    lateinit var userReactiveService: UserReactiveService

    @GetMapping("/reactive/find")
    fun findByReactive(@RequestParam age: Int?, @RequestParam city: String?) = userReactiveService.find(age, city)

    @GetMapping("/reactive/generate")
    fun genDataByReactive() = userReactiveService.generateData()

    ......    
}

创建用户的方式：

curl http://localhost:8080/user/reactive/generate

基于城市查询用户的方式：

curl http://localhost:8080/user/reactive/find?city=suzhou

RxJava 2

RxJava 库是 JVM 上响应式编程的先驱，也是响应式流规范(Reactive Streams)的基础。

如果对 RxJava 2 不熟悉，也可以购买我的《RxJava 2.x 实战》

2.1 创建 Repository

创建 UserRxJavaRepository 功能跟 UserReactiveRepository 一样，只是多了一个 findUserByName() 方法。

import com.kotlin.tutorial.model.User
import io.reactivex.Flowable
import org.springframework.data.repository.reactive.RxJava2CrudRepository
import org.springframework.stereotype.Repository

/**
 * Created by tony on 2018/11/22.
 */
@Repository
interface UserRxJavaRepository : RxJava2CrudRepository<User, String> {

    fun findUserByName(name: String): Flowable<User>

    fun findUserByAge(age: Int): Flowable<User>

    fun findUserByAddressCity(city: String): Flowable<User>

    fun findUserByAgeAndAddressCity(age: Int, city: String): Flowable<User>
}

2.2 创建 JavaService

创建 UserRxJavaService ，类似于 UserReactiveService。但是，多了两个方法：findByName()、login()。其中，调用 login() 会添加一条审计的记录。

import com.kotlin.tutorial.Utils.toLower
import com.kotlin.tutorial.model.Address
import com.kotlin.tutorial.model.Audit
import com.kotlin.tutorial.model.User
import com.kotlin.tutorial.repository.AuditRepository
import com.kotlin.tutorial.repository.UserRxJavaRepository
import io.reactivex.Flowable
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.stereotype.Component
import java.time.LocalDateTime

/**
 * Created by tony on 2018/11/22.
 */
@Component
class UserRxJavaService {

    @Autowired
    lateinit var userRepository: UserRxJavaRepository

    @Autowired
    lateinit var auditRepository: AuditRepository

    companion object {

        val cities = listOf("Shanghai", "Suzhou", "Hangzhou").toLower()
        val streets = listOf("renming road", "zhongshan road").toLower()
    }

    fun findByName(name: String): Flowable<User> = userRepository.findUserByName(name)

    fun find(age: Int?, rawCity: String?): Flowable<User> {

        val city = rawCity?.toLowerCase()

        return when {

            age is Int && city is String -> userRepository.findUserByAgeAndAddressCity(age, city)

            city is String -> userRepository.findUserByAddressCity(city)

            age is Int -> userRepository.findUserByAge(age)

            else -> userRepository.findAll()
        }
    }

    fun generateData(): Flowable<User> {

        val list = listOf(20, 25, 33, 28, 34).map {

            val u = generate(it)

            auditRepository.save(Audit(u.name, LocalDateTime.now()))

            u
        }

        return userRepository.deleteAll().andThen(userRepository.saveAll(list))
    }

    private fun generate(age: Int): User {

        val address = Address(age, streets[age % streets.size], cities[age % cities.size])

        return User("Tony$age", age, address)
    }

    fun login(name: String) =
            userRepository.findUserByName(name)
            .map {
                auditRepository.save(Audit(it.name, LocalDateTime.now()))
            }
}

2.3 创建 Controller

在原有的 UserController 中新增两个 rxjava 的接口：

@RestController
@RequestMapping("/user")
class UserController {

    @Autowired
    lateinit var userRxJavaService: UserRxJavaService

    @GetMapping("/rxjava/find")
    fun findByRx(@RequestParam age: Int?, @RequestParam city: String?) = userRxJavaService.find(age, city)

    @GetMapping("/rxjava/generate")
    fun genDateByRx() = userRxJavaService.generateData()

    ...... 
}

Kotlin 1.3 的 Coroutines

协程(coroutine)相比于线程更加轻量级，协程又称为微线程。线程和协程的一个显著区别是，线程的阻塞代价是昂贵的，而协程使用了更简单、代价更小的挂起(suspend)来代替阻塞。

Coroutines 是 Kotlin 1.1 增加的实验的功能，到 Kotlin 1.3 已经变成了正式的功能。

先在 UserController 创建一个模拟登陆的接口，访问该接口时会添加一条审计的记录

    @GetMapping("/rxjava/login")
    fun mockLogin(@RequestParam username: String) = userRxJavaService.login(username)

然后尝试用传统的 blocking 方式来编写一个获取登陆信息的接口：

    @GetMapping("/blocking/{username}")
    fun getNormalLoginMessage(@PathVariable username: String):String {

        val user = userService.findByName(username)

        val lastLoginTime = auditService.findByName(user.name).eventDate

        return "Hi ${user.name}, you have logged in since $lastLoginTime"
    }

再尝试用 RxJava 的方式来编写该接口：

    @GetMapping("/rxjava/{username}")
    fun getRxLoginMessage(@PathVariable username: String)=
            userRxJavaService.findByName(username)
                    .map {

                        auditService.findByName(it.name).eventDate
                    }
                    .map {

                        "Hi ${username}, you have logged in since $it"
                    }

最后，使用 Coroutines 的方式来编写接口：

    @GetMapping("/coroutine/{username}")
    fun getLoginMessage(@PathVariable username: String) = runBlocking {

        val user = userRxJavaService.findByName(username).awaitSingle()

        val lastLoginTime = GlobalScope.async {

            auditService.findByName(user.name).eventDate

        }.await()

        "Hi ${user.name}, you have logged in since $lastLoginTime"
    }