前言Spring官方最近宣布，将在Spring Framework 5 0版本中正式支持Kotlin语言。这意味着Spring Boot 2 x版本将为Kotl
前言
Spring官方最近宣布，将在Spring Framework 5.0版本中正式支持Kotlin语言。这意味着Spring Boot 2.x版本将为Kotlin提供一流的支持。
这并不会令人意外，因为Pivotal团队以广泛接纳JVM语言（如Scala和Groovy）而闻名。
Kotlin 是一个基于 JVM 的编程语言，它的简洁、便利早已不言而喻。Kotlin 能够胜任 Java 做的所有事。目前，我们公司 C 端 的 Android 产品全部采用 Kotlin 编写。公司的后端项目也可能会使用 Kotlin，所以我给他们做一些 demo 进行演示。
示例一：结合 Redis 进行数据存储和查询
1.1 配置 gradle
在build.gradle中添加插件和依赖的库。
plugins {
id 'java'
id 'org.jetbrains.kotlin.jvm' version '1.3.0'
}
ext {
libraries = [
rxjava : "2.2.2",
logback : "1.2.3",
spring_boot : "2.1.0.RELEASE",
commons_pool2 : "2.6.0",
fastjson : "1.2.51"
]
}
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:1.3.0"
testCompile group: 'junit', name: 'junit', version: '4.12'
implementation "io.reactivex.rxjava2:rxjava:${libs.rxjava}"
implementation "ch.qos.logback:logback-classic:${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:${libs.spring_boot}"
implementation "org.springframework.boot:spring-boot-starter-data-redis:${libs.spring_boot}"
implementation "org.apache.commons:commons-pool2:${libs.commons_pool2}"
implementation "com.alibaba:fastjson:${libs.fastjson}"
}
compileKotlin {
kotlinOptions.jvmTarget = "1.8"
}
compileTestKotlin {
kotlinOptions.jvmTarget = "1.8"
}
1.2 创建 SpringKotlinApplication：
import org.springframework.boot.SpringApplication
import org.springframework.boot.autoconfigure.SpringBootApplication
/**
* Created by tony on 2018/11/13.
*/
@SpringBootApplication
open class SpringKotlinApplication
fun main(args: Array<String>) {
SpringApplication.run(SpringKotlinApplication::class.java, *args)
}
需要注意open的使用，如果不加open会报如下的错误：
org.springframework.beans.factory.parsing.BeanDefinitionParsingException: Configuration problem: @Configuration class 'SpringKotlinApplication' may not be final. Remove the final modifier to continue.
因为 Kotlin 的类默认是final的，所以这里需要使用open关键字。
1.3 配置 redis
在 application.yml 中添加 redis 的配置
spring: redis: #数据库索引 database: 0 host: 127.0.0.1 port: 6379 password: lettuce: pool: #最大连接数 max-active: 8 #最大阻塞等待时间(负数表示没限制) max-wait: -1 #最大空闲 max-idle: 8 #最小空闲 min-idle: 0 #连接超时时间 timeout: 10000
接下来定义 redis 的序列化器，本文采用fastjson，当然使用gson、jackson等都可以，看个人喜好。
import com.alibaba.fastjson.JSON
import com.alibaba.fastjson.serializer.SerializerFeature
import org.springframework.data.redis.serializer.RedisSerializer
import org.springframework.data.redis.serializer.SerializationException
import java.nio.charset.Charset
/**
* Created by tony on 2018/11/13.
*/
class FastJsonRedisSerializer<T>(private val clazz: Class<T>) : RedisSerializer<T> {
@Throws(SerializationException::class)
override fun serialize(t: T?) = if (null == t) {
ByteArray(0)
} else JSON.toJSONString(t, SerializerFeature.WriteClassName).toByteArray(DEFAULT_CHARSET)
@Throws(SerializationException::class)
override fun deserialize(bytes: ByteArray?): T? {
if (null == bytes || bytes.size <= 0) {
return null
}
val str = String(bytes, DEFAULT_CHARSET)
return JSON.parseObject(str, clazz) as T
}
companion object {
private val DEFAULT_CHARSET = Charset.forName("UTF-8")
}
}
创建 RedisConfig
import org.springframework.data.redis.core.RedisTemplate
import org.springframework.data.redis.connection.RedisConnectionFactory
import org.springframework.context.annotation.Bean
import org.springframework.data.redis.cache.RedisCacheManager
import org.springframework.cache.CacheManager
import org.springframework.cache.annotation.CachingConfigurerSupport
import org.springframework.cache.annotation.EnableCaching
import org.springframework.context.annotation.Configuration
import org.springframework.data.redis.serializer.StringRedisSerializer
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean
import org.springframework.boot.context.properties.EnableConfigurationProperties
import org.springframework.data.redis.core.RedisOperations
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass
import org.springframework.boot.autoconfigure.data.redis.RedisProperties
/**
* Created by tony on 2018/11/13.
*/
@EnableCaching
@Configuration
@ConditionalOnClass(RedisOperations::class)
@EnableConfigurationProperties(RedisProperties::class)
open class RedisConfig : CachingConfigurerSupport() {
@Bean(name = arrayOf("redisTemplate"))
@ConditionalOnMissingBean(name = arrayOf("redisTemplate"))
open fun redisTemplate(redisConnectionFactory: RedisConnectionFactory): RedisTemplate<Any, Any> {
val template = RedisTemplate<Any, Any>()
val fastJsonRedisSerializer = FastJsonRedisSerializer(Any::class.java)
template.valueSerializer = fastJsonRedisSerializer
template.hashValueSerializer = fastJsonRedisSerializer
template.keySerializer = StringRedisSerializer()
template.hashKeySerializer = StringRedisSerializer()
template.connectionFactory = redisConnectionFactory
return template
}
//缓存管理器
@Bean
open fun cacheManager(redisConnectionFactory: RedisConnectionFactory): CacheManager {
val builder = RedisCacheManager
.RedisCacheManagerBuilder
.fromConnectionFactory(redisConnectionFactory)
return builder.build()
}
}
这里也都需要使用open，理由同上。
1.4 创建 Service
创建一个 User 对象，使用 datat class 类型。
data class User(var userName:String,var password:String):Serializable
创建操作 User 的Service接口
import com.kotlin.tutorial.user.User
/**
* Created by tony on 2018/11/13.
*/
interface IUserService {
fun getUser(username: String): User
fun createUser(username: String,password: String)
}
创建 Service 的实现类：
import com.kotlin.tutorial.user.User
import com.kotlin.tutorial.user.service.IUserService
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.data.redis.core.RedisTemplate
import org.springframework.stereotype.Service
/**
* Created by tony on 2018/11/13.
*/
@Service
class UserServiceImpl : IUserService {
@Autowired
lateinit var redisTemplate: RedisTemplate<Any, Any>
override fun getUser(username: String): User {
var user = redisTemplate.opsForValue().get("user_${username}")
if (user == null) {
user = User("default","000000")
}
return user as User
}
override fun createUser(username: String, password: String) {
redisTemplate.opsForValue().set("user_${username}", User(username, password))
}
}
1.5 创建 Controller
创建一个 UserController，包含 createUser、getUser 两个接口。
import com.kotlin.tutorial.user.User
import com.kotlin.tutorial.user.service.IUserService
import com.kotlin.tutorial.web.dto.HttpResponse
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.web.bind.annotation.GetMapping
import org.springframework.web.bind.annotation.RequestMapping
import org.springframework.web.bind.annotation.RequestParam
import org.springframework.web.bind.annotation.RestController
/**
* Created by tony on 2018/11/13.
*/
@RestController
@RequestMapping("/user")
class UserController {
@Autowired
lateinit var userService: IUserService
@GetMapping("/getUser")
fun getUser(@RequestParam("name") userName: String): HttpResponse<User> {
return HttpResponse(userService.getUser(userName))
}
@GetMapping("/createUser")
fun createUser(@RequestParam("name") userName: String,@RequestParam("password") password: String): HttpResponse<String> {
userService.createUser(userName,password)
return HttpResponse("create ${userName} success")
}
}
创建完 Controller 之后，可以进行测试了。
创建用户tony：
查询用户tony：
创建用户monica：
查询用户monica：
示例二：结合 RxJava 模拟顺序、并发地执行任务
2.1 创建 MockTask
首先定义一个任务接口，所有的任务都需要实现该接口：
/**
* Created by tony on 2018/11/13.
*/
interface ITask {
fun execute()
}
再创建一个模拟的任务，其中delayInSeconds用来模拟任务所花费的时间，单位是秒。
import java.util.concurrent.TimeUnit
import com.kotlin.tutorial.task.ITask
/**
* Created by tony on 2018/11/13.
*/
class MockTask(private val delayInSeconds: Int) : ITask {
/**
* Stores information if task was started.
*/
var started: Boolean = false
/**
* Stores information if task was successfully finished.
*/
var finishedSuccessfully: Boolean = false
/**
* Stores information if the task was interrupted.
* It can happen if the thread that is running this task was killed.
*/
var interrupted: Boolean = false
/**
* Stores the thread identifier in which the task was executed.
*/
var threadId: Long = 0
override fun execute() {
try {
this.threadId = Thread.currentThread().id
this.started = true
TimeUnit.SECONDS.sleep(delayInSeconds.toLong())
this.finishedSuccessfully = true
} catch (e: InterruptedException) {
this.interrupted = true
}
}
}
2.2 创建 ConcurrentTasksExecutor
顺序执行的话比较简单，一个任务接着一个任务地完成即可，是单线程的操作。
对于并发而言，在这里借助 RxJava 的 merge 操作符来将多个任务进行合并。还用到了 RxJava 的任务调度器 Scheduler，createScheduler()是按照所需的线程数来创建Scheduler的。
import com.kotlin.tutorial.task.ITask
import io.reactivex.Completable
import io.reactivex.schedulers.Schedulers
import org.slf4j.LoggerFactory
import org.springframework.util.CollectionUtils
import java.util.*
import java.util.concurrent.Executors
import java.util.stream.Collectors
/**
* Created by tony on 2018/11/13.
*/
class ConcurrentTasksExecutor(private val numberOfConcurrentThreads: Int, private val tasks: Collection<ITask>?) : ITask {
val log = LoggerFactory.getLogger(this.javaClass)
constructor(numberOfConcurrentThreads: Int, vararg tasks: ITask) : this(numberOfConcurrentThreads, if (tasks == null) null else Arrays.asList<ITask>(*tasks)) {}
init {
if (numberOfConcurrentThreads < 0) {
throw RuntimeException("Amount of threads must be higher than zero.")
}
}
/**
* Converts collection of tasks (except null tasks) to collection of completable actions.
* Each action will be executed in thread according to the scheduler created with [.createScheduler] method.
*
* @return list of completable actions
*/
private val asConcurrentTasks: List<Completable>
get() {
if (tasks!=null) {
val scheduler = createScheduler()
return tasks.stream()
.filter { task -> task != null }
.map { task ->
Completable
.fromAction {
task.execute()
}
.subscribeOn(scheduler)
}
.collect(Collectors.toList())
} else {
return ArrayList<Completable>()
}
}
/**
* Checks whether tasks collection is empty.
*
* @return true if tasks collection is null or empty, false otherwise
*/
private val isTasksCollectionEmpty: Boolean
get() = CollectionUtils.isEmpty(tasks)
/**
* Executes all tasks concurrent way only if collection of tasks is not empty.
* Method completes when all of the tasks complete (or one of them fails).
* If one of the tasks failed the the exception will be rethrown so that it can be handled by mechanism that calls this method.
*/
override fun execute() {
if (isTasksCollectionEmpty) {
log.warn("There are no tasks to be executed.")
return
}
log.debug("Executing #{} tasks concurrent way.", tasks?.size)
Completable.merge(asConcurrentTasks).blockingAwait()
}
/**
* Creates a scheduler that will be used for executing tasks concurrent way.
* Scheduler will use number of threads defined in [.numberOfConcurrentThreads]
*
* @return scheduler
*/
private fun createScheduler() = Schedulers.from(Executors.newFixedThreadPool(numberOfConcurrentThreads))
}
2.3 创建 Controller
创建一个 TasksController，包含 sequential、concurrent 两个接口，会分别把sequential 和 concurrent 执行任务的时间展示出来。
import com.kotlin.tutorial.task.impl.ConcurrentTasksExecutor
import com.kotlin.tutorial.task.impl.MockTask
import com.kotlin.tutorial.web.dto.TaskResponse
import com.kotlin.tutorial.web.dto.ErrorResponse
import com.kotlin.tutorial.web.dto.HttpResponse
import org.springframework.http.HttpStatus
import org.springframework.util.StopWatch
import org.springframework.web.bind.annotation.*
import java.util.stream.Collectors
import java.util.stream.IntStream
/**
* Created by tony on 2018/11/13.
*/
@RestController
@RequestMapping("/tasks")
class TasksController {
@GetMapping("/sequential")
fun sequential(@RequestParam("task") taskDelaysInSeconds: IntArray): HttpResponse<TaskResponse> {
val watch = StopWatch()
watch.start()
IntStream.of(*taskDelaysInSeconds)
.mapToObj{
MockTask(it)
}
.forEach{
it.execute()
}
watch.stop()
return HttpResponse(TaskResponse(watch.totalTimeSeconds))
}
@GetMapping("/concurrent")
fun concurrent(@RequestParam("task") taskDelaysInSeconds: IntArray, @RequestParam("threads",required = false,defaultValue = "1") numberOfConcurrentThreads: Int): HttpResponse<TaskResponse> {
val watch = StopWatch()
watch.start()
val delayedTasks = IntStream.of(*taskDelaysInSeconds)
.mapToObj{
MockTask(it)
}
.collect(Collectors.toList())
ConcurrentTasksExecutor(numberOfConcurrentThreads, delayedTasks).execute()
watch.stop()
return HttpResponse(TaskResponse(watch.totalTimeSeconds))
}
@ExceptionHandler(IllegalArgumentException::class)
@ResponseStatus(HttpStatus.BAD_REQUEST)
fun handleException(e: IllegalArgumentException) = ErrorResponse(e.message)
}
顺序地执行多个任务：http://localhost:8080/tasks/sequential?task=1&task=2&task=3&task=4
每个任务所花费的时间分别是1秒、2秒、3秒和4秒。最后，一共花费了10.009秒。
两个线程并发地执行多个任务：http://localhost:8080/tasks/concurrent?task=1&task=2&task=3&task=4&threads=2
三个线程并发地执行多个任务：http://localhost:8080/tasks/concurrent?task=1&task=2&task=3&task=4&threads=3
总结
本文使用了 Kotlin 的特性跟 Spring Boot 整合进行后端开发。Kotlin 的很多语法糖使得开发变得更加便利，当然 Kotlin 也是 Java 的必要补充。
本文 demo 的 github 地址：https://github.com/fengzhizi715/kotlin-spring-demo
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