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。
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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 = 1.8def 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：
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import org.springframework.boot.springapplicationimport org.springframework.boot.autoconfigure.springbootapplication/*** created by tony on 2018/11/13.*/@springbootapplicationopen class springkotlinapplicationfun 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
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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。
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import com.alibaba.fastjson.jsonimport com.alibaba.fastjson.serializer.serializerfeatureimport org.springframework.data.redis.serializer.redisserializerimport org.springframework.data.redis.serializer.serializationexceptionimport 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
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import org.springframework.data.redis.core.redistemplateimport org.springframework.data.redis.connection.redisconnectionfactoryimport org.springframework.context.annotation.beanimport org.springframework.data.redis.cache.rediscachemanagerimport org.springframework.cache.cachemanagerimport org.springframework.cache.annotation.cachingconfigurersupportimport org.springframework.cache.annotation.enablecachingimport org.springframework.context.annotation.configurationimport org.springframework.data.redis.serializer.stringredisserializerimport org.springframework.boot.autoconfigure.condition.conditionalonmissingbeanimport org.springframework.boot.context.properties.enableconfigurationpropertiesimport org.springframework.data.redis.core.redisoperationsimport org.springframework.boot.autoconfigure.condition.conditionalonclassimport 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。
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data class user(var username:string,var password:string):serializable |
创建操作 user 的service接口
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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：
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import com.kotlin.tutorial.user.userimport com.kotlin.tutorial.user.service.iuserserviceimport org.springframework.beans.factory.annotation.autowiredimport org.springframework.data.redis.core.redistemplateimport org.springframework.stereotype.service/** * created by tony on 2018/11/13. */@serviceclass 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。
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import com.kotlin.tutorial.user.userimport com.kotlin.tutorial.user.service.iuserserviceimport com.kotlin.tutorial.web.dto.httpresponseimport org.springframework.beans.factory.annotation.autowiredimport org.springframework.web.bind.annotation.getmappingimport org.springframework.web.bind.annotation.requestmappingimport org.springframework.web.bind.annotation.requestparamimport 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：
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/** * 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。
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import java.util.concurrent.timeunitimport 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。
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import com.kotlin.tutorial.task.itaskimport io.reactivex.completableimport io.reactivex.schedulers.schedulersimport org.slf4j.loggerfactoryimport org.springframework.util.collectionutilsimport java.util.*import java.util.concurrent.executorsimport 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。
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import com.kotlin.tutorial.task.impl.concurrenttasksexecutorimport com.kotlin.tutorial.task.impl.mocktaskimport com.kotlin.tutorial.web.dto.taskresponseimport com.kotlin.tutorial.web.dto.errorresponseimport com.kotlin.tutorial.web.dto.httpresponseimport org.springframework.http.httpstatusimport org.springframework.util.stopwatchimport org.springframework.web.bind.annotation.*import java.util.stream.collectorsimport 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
好了，以上就是这篇文章的全部内容了，希望本文的内容对大家的学习或者工作具有一定的参考学习价值，如果有疑问大家可以留言交流，谢谢大家对服务器之家的支持。
原文链接：https://juejin.im/post/5bebb4436fb9a04a072feb74
