利用Kotlin + Spring Boot实现后端开发

这篇文章主要给大家介绍了关于利用Kotlin + Spring Boot实现后端开发的相关资料，文中通过示例代码介绍的非常详细，对大家的学习或者工作具有一定的参考学习价值，需要的朋友们下面随着小编来一起学习学习吧

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) { 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(private val clazz: Class) : RedisSerializer { @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 { val template = RedisTemplate() 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 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 { return HttpResponse(userService.getUser(userName)) } @GetMapping("/createUser") fun createUser(@RequestParam("name") userName: String,@RequestParam("password") password: String): HttpResponse { 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 { val log = LoggerFactory.getLogger(this.javaClass) constructor(numberOfConcurrentThreads: Int, vararg tasks: ITask) : this(numberOfConcurrentThreads, if (tasks == null) null else Arrays.asList(*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 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() } } /** * 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 { 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 { 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