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SpringBoot 与 Kotlin 完美交融

本文讲解 Spring Boot2 基础下，如何使用 Kotlin，并无缝整合与完美交融。为了让读者更加熟悉 Kotlin 的语法糖，笔者会在未来的几篇文章中，聊聊 Kotlin 的新特性及其语法糖。

环境依赖

修改 POM 文件，添加 spring boot 依赖。

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.0.2.RELEASE</version>
    <relativePath/>
</parent>
<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-jdbc</artifactId>
    </dependency>
</dependencies>

紧接着，我们需要添加 mysql 依赖。

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>5.1.35</version>
</dependency>
<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>druid</artifactId>
    <version>1.0.14</version>
</dependency>

最后，添加 Kotlin 依赖。

<dependency>
    <groupId>org.jetbrains.kotlin</groupId>
    <artifactId>kotlin-stdlib-jdk8</artifactId>
</dependency>
<dependency>
    <groupId>org.jetbrains.kotlin</groupId>
    <artifactId>kotlin-reflect</artifactId>
</dependency>
<dependency>
    <groupId>org.jetbrains.kotlin</groupId>
    <artifactId>kotlin-stdlib</artifactId>
</dependency>

注意的是，在 Kotlin 中，data class 默认没有无参构造方法，并且 data class 默认为 final 类型，不可以被继承。注意的是，如果我们使用 Spring + Kotlin 的模式，那么使用 @autowared 就可能遇到这个问题。因此，我们可以添加 NoArg 为标注的类生成无参构造方法。使用 AllOpen 为被标注的类去掉 final，允许被继承。

<plugin>
    <artifactId>kotlin-maven-plugin</artifactId>
    <groupId>org.jetbrains.kotlin</groupId>
    <version>${kotlin.version}</version>
    <executions>
        <execution>
            <id>compile</id>
            <goals> <goal>compile</goal> </goals>
        </execution>
        <execution>
            <id>test-compile</id>
            <goals> <goal>test-compile</goal> </goals>
        </execution>
    </executions>
    <dependencies>
        <dependency>
            <groupId>org.jetbrains.kotlin</groupId>
            <artifactId>kotlin-maven-noarg</artifactId>
            <version>${kotlin.version}</version>
        </dependency>
        <dependency>
            <groupId>org.jetbrains.kotlin</groupId>
            <artifactId>kotlin-maven-allopen</artifactId>
            <version>${kotlin.version}</version>
        </dependency>
    </dependencies>
</plugin>

至此，我们 Maven 的依赖环境大致配置完毕。完整的源码，可以参见文末 GitHub 仓库。

数据源

方案一使用 Spring Boot 默认配置

使用 Spring Boot 默认配置，不需要在创建 dataSource 和 jdbcTemplate 的 Bean。

在 src/main/resources/application.properties 中配置数据源信息。

spring.datasource.driver-class-name=com.mysql.jdbc.Driver
spring.datasource.url=jdbc:mysql://localhost:3307/springboot_db
spring.datasource.username=root
spring.datasource.password=root

方案二手动创建

在 src/main/resources/config/source.properties 中配置数据源信息。

# mysql
source.driverClassName = com.mysql.jdbc.Driver
source.url = jdbc:mysql://localhost:3306/springboot_db
source.username = root
source.password = root

这里，创建 dataSource 和jdbcTemplate。

@Configuration
@EnableTransactionManagement
@PropertySource(value = *arrayOf("classpath:config/source.properties"))
open class BeanConfig {

    @Autowired
    private lateinit var env: Environment

    @Bean
    open fun dataSource(): DataSource {
        val dataSource = DruidDataSource()
        dataSource.driverClassName = env!!.getProperty("source.driverClassName").trim()
        dataSource.url = env.getProperty("source.url").trim()
        dataSource.username = env.getProperty("source.username").trim()
        dataSource.password = env.getProperty("source.password").trim()
        return dataSource
    }

    @Bean
    open fun jdbcTemplate(): JdbcTemplate {
        val jdbcTemplate = JdbcTemplate()
        jdbcTemplate.dataSource = dataSource()
        return jdbcTemplate
    }
}

脚本初始化

先初始化需要用到的 SQL 脚本。

CREATE DATABASE /*!32312 IF NOT EXISTS*/`springboot_db` /*!40100 DEFAULT CHARACTER SET utf8 */;

USE `springboot_db`;

DROP TABLE IF EXISTS `t_author`;

CREATE TABLE `t_author` (
  `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT COMMENT '用户ID',
  `real_name` varchar(32) NOT NULL COMMENT '用户名称',
  `nick_name` varchar(32) NOT NULL COMMENT '用户匿名',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;

使用 JdbcTemplate 操作

实体对象

class Author {
    var id: Long? = null
    var realName: String? = null
    var nickName: String? = null
}

DAO相关

interface AuthorDao {
    fun add(author: Author): Int
    fun update(author: Author): Int
    fun delete(id: Long): Int
    fun findAuthor(id: Long): Author?
    fun findAuthorList(): List<Author>
}

我们来定义实现类，通过 JdbcTemplate 定义的数据访问操作。

@Repository
open class AuthorDaoImpl : AuthorDao {

    @Autowired
    private lateinit var jdbcTemplate: JdbcTemplate

    override fun add(author: Author): Int {
        return jdbcTemplate.update("insert into t_author(real_name, nick_name) values(?, ?)",
                author.realName, author.nickName)
    }

    override fun update(author: Author): Int {
        return jdbcTemplate.update("update t_author set real_name = ?, nick_name = ? where id = ?",
                *arrayOf(author.realName, author.nickName, author.id))
    }

    override fun delete(id: Long): Int {
        return jdbcTemplate.update("delete from t_author where id = ?", id)
    }

    override fun findAuthor(id: Long): Author? {
        val list = jdbcTemplate.query<Author>("select * from t_author where id = ?",
                arrayOf<Any>(id), BeanPropertyRowMapper(Author::class.java))
        return list?.get(0);
    }

    override fun findAuthorList(): List<Author> {
        return jdbcTemplate.query("select * from t_author", arrayOf(), BeanPropertyRowMapper(Author::class.java))
    }
}

Service相关

interface AuthorService {
    fun add(author: Author): Int
    fun update(author: Author): Int
    fun delete(id: Long): Int
    fun findAuthor(id: Long): Author?
    fun findAuthorList(): List<Author>
}

我们来定义实现类，Service 层调用 Dao 层的方法，这个是典型的套路。

@Service("authorService")
open class AuthorServiceImpl : AuthorService {

    @Autowired
    private lateinit var authorDao: AuthorDao

    override fun update(author: Author): Int {
        return this.authorDao.update(author)
    }

    override fun add(author: Author): Int {
        return this.authorDao.add(author)
    }

    override fun delete(id: Long): Int {
        return this.authorDao.delete(id)
    }

    override fun findAuthor(id: Long): Author? {
        return this.authorDao.findAuthor(id)
    }

    override fun findAuthorList(): List<Author> {
        return this.authorDao.findAuthorList()
    }
}

Controller相关

为了展现效果，我们先定义一组简单的 RESTful API 接口进行测试。

@RestController
@RequestMapping(value = "/authors")
class AuthorController {

    @Autowired
    private lateinit var authorService: AuthorService

    /**
     * 查询用户列表
     */
    @RequestMapping(method = [RequestMethod.GET])
    fun getAuthorList(request: HttpServletRequest): Map<String, Any> {
        val authorList = this.authorService.findAuthorList()
        val param = HashMap<String, Any>()
        param["total"] = authorList.size
        param["rows"] = authorList
        return param
    }

    /**
     * 查询用户信息
     */
    @RequestMapping(value = "/{userId://d+}", method = [RequestMethod.GET])
    fun getAuthor(@PathVariable userId: Long, request: HttpServletRequest): Author {
        return authorService.findAuthor(userId) ?: throw RuntimeException("查询错误")
    }

    /**
     * 新增方法
     */
    @RequestMapping(method = [RequestMethod.POST])
    fun add(@RequestBody jsonObject: JSONObject) {
        val userId = jsonObject.getString("user_id")
        val realName = jsonObject.getString("real_name")
        val nickName = jsonObject.getString("nick_name")

        val author = Author()
        author.id = java.lang.Long.valueOf(userId)
        author.realName = realName
        author.nickName = nickName
        try {
            this.authorService.add(author)
        } catch (e: Exception) {
            throw RuntimeException("新增错误")
        }
    }

    /**
     * 更新方法
     */
    @RequestMapping(value = "/{userId://d+}", method = [RequestMethod.PUT])
    fun update(@PathVariable userId: Long, @RequestBody jsonObject: JSONObject) {
        var author = this.authorService.findAuthor(userId)
        val realName = jsonObject.getString("real_name")
        val nickName = jsonObject.getString("nick_name")
        try {
            if (author != null) {
                author.realName = realName
                author.nickName = nickName
                this.authorService.update(author)
            }
        } catch (e: Exception) {
            throw RuntimeException("更新错误")
        }

    }

    /**
     * 删除方法
     */
    @RequestMapping(value = "/{userId://d+}", method = [RequestMethod.DELETE])
    fun delete(@PathVariable userId: Long) {
        try {
            this.authorService.delete(userId)
        } catch (e: Exception) {
            throw RuntimeException("删除错误")
        }
    }
}

最后，我们通过 SpringKotlinApplication 运行程序。

@SpringBootApplication(scanBasePackages = ["com.lianggzone.demo.kotlin"])
open class SpringKotlinApplication{
    fun main(args: Array<String>) {
        SpringApplication.run(SpringKotlinApplication::class.java, *args)
    }
}

关于测试

这里，笔者推荐 IDEA 的 Editor REST Client。IDEA 的 Editor REST Client 在 IntelliJ IDEA 2017.3 版本就开始支持，在 2018.1 版本添加了很多的特性。事实上，它是 IntelliJ IDEA 的 HTTP Client 插件。参见笔者之前的另一篇文章：快速测试 API 接口的新技能 | 梁桂钊的博客

### 查询用户列表
GET http://localhost:8080/authors
Accept : application/json
Content-Type : application/json;charset=UTF-8

### 查询用户信息
GET http://localhost:8080/authors/15
Accept : application/json
Content-Type : application/json;charset=UTF-8

### 新增方法
POST http://localhost:8080/authors
Content-Type: application/json

{
    "user_id": "21",
    "real_name": "梁桂钊",
    "nick_name": "梁桂钊"
}

### 更新方法
PUT http://localhost:8080/authors/21
Content-Type: application/json

{
    "real_name" : "lianggzone",
    "nick_name": "lianggzone"
}

### 删除方法
DELETE http://localhost:8080/authors/21
Accept : application/json
Content-Type : application/json;charset=UTF-8

原文 http://blog.720ui.com/2018/springboot2_kotlin_prime/

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