利用Kotlin + Spring Boot实现后端开发

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

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