Kotlin + SpringBoot로 최소 WebAPI 구축

개요

Kotlin + SpringBoot를 다루어 보았으므로 환경 구축 메모입니다.

Spring Data JPA로 테이블 액세스 해, JSON 형식으로 브라우저에 반환하는 곳까지를 쓰고 있습니다.

Spring 프로젝트 만들기

Spring Initializr 을 사용합니다.

설정은 아래와 같이 했습니다.

IntelliJ IDEA 다운로드

IntelliJ IDEA를 다운로드합니다.

Community판(무료)으로 괜찮습니다.

만든 프로젝트 가져오기

IntelliJ IDEA에서 [File] -> [Open...]을 선택하여 만든 프로젝트를 가져옵니다.

JPA 코멘트 아웃

build.gradle.kts

dependencies {
//  implementation("org.springframework.boot:spring-boot-starter-data-jpa")
    implementation("org.springframework.boot:spring-boot-starter-web")
    implementation("com.fasterxml.jackson.module:jackson-module-kotlin")
    implementation("org.jetbrains.kotlin:kotlin-reflect")
    implementation("org.jetbrains.kotlin:kotlin-stdlib-jdk8")
    compileOnly("org.projectlombok:lombok")
    annotationProcessor("org.projectlombok:lombok")
    testImplementation("org.springframework.boot:spring-boot-starter-test")
}

컨트롤러 작성

Controller 클래스를 작성합니다.

미리 controller 패키지를 작성하십시오.

DemoController.kt

package com.example.demo.controller

import org.springframework.http.MediaType
import org.springframework.http.ResponseEntity
import org.springframework.web.bind.annotation.GetMapping
import org.springframework.web.bind.annotation.RequestMapping
import org.springframework.web.bind.annotation.RestController

@RestController
@RequestMapping("/demo")
class DemoController {

    @GetMapping("/getAll")
    fun getAll(): ResponseEntity<String> {
        return ResponseEntity.ok("Demo")
    }

}

프로젝트 시작

[View] -> [Tool Windows] -> [Gradle] -> [Tasks] -> [application] -> [bootRun]을 선택하여 프로젝트를 실행합니다.

아래와 같은 로그가 나오면 OK입니다.

18:32:18: Executing task 'bootRun'...

> Task :compileKotlin
> Task :compileJava NO-SOURCE
> Task :processResources UP-TO-DATE
> Task :classes UP-TO-DATE
> Task :bootRunMainClassName

> Task :bootRun

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::                (v2.4.3)

2021-03-13 18:32:21.905  INFO 8184 --- [           main] com.example.demo.DemoApplicationKt       : Starting DemoApplicationKt using Java 1.8.0_241 on DESKTOP-I88K5MF with PID 8184 
2021-03-13 18:32:21.905  INFO 8184 --- [           main] com.example.demo.DemoApplicationKt       : No active profile set, falling back to default profiles: default
2021-03-13 18:32:23.034  INFO 8184 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2021-03-13 18:32:23.050  INFO 8184 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2021-03-13 18:32:23.050  INFO 8184 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.43]
2021-03-13 18:32:23.128  INFO 8184 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2021-03-13 18:32:23.128  INFO 8184 --- [           main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 1155 ms
2021-03-13 18:32:23.425  INFO 8184 --- [           main] o.s.s.concurrent.ThreadPoolTaskExecutor  : Initializing ExecutorService 'applicationTaskExecutor'
2021-03-13 18:32:23.662  INFO 8184 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2021-03-13 18:32:23.677  INFO 8184 --- [           main] com.example.demo.DemoApplicationKt       : Started DemoApplicationKt in 2.308 seconds (JVM running for 2.822)
2021-03-13 18:32:26.108  INFO 8184 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring DispatcherServlet 'dispatcherServlet'
2021-03-13 18:32:26.108  INFO 8184 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : Initializing Servlet 'dispatcherServlet'
2021-03-13 18:32:26.116  INFO 8184 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : Completed initialization in 8 ms

브라우저에서 http://localhost:8080/demo/getAll 표시 → Demo가 표시됩니다.

JPA로 데이터 액세스를 위해 Mysql 준비

테이블을 만들어 둡니다.

create database demo;
use demo;
create table demo (
    id int auto_increment,
    name varchar(256),
    PRIMARY KEY (id)
);
insert into demo (name) values ("test");

application.properties에 설정 추가

application.properties

spring.datasource.url=jdbc:mysql://localhost:3306/demo?useUnicode=true&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC
spring.datasource.username=root
spring.datasource.password=root
spring.datasource.driverClassName=com.mysql.jdbc.Driver
spring.jpa.database=MYSQL
spring.jpa.hibernate.ddl-auto=update

참고:
Java에서 DB (MySQL) 연결을 시도하면 오류가 발생하는 솔루션
SpringBoot + Spring JPA로 데이터베이스에 연결

JPA를 주석 처리하고 드라이버 추가

build.gradle.kts

dependencies {
+   implementation("org.springframework.boot:spring-boot-starter-data-jpa")
    implementation("org.springframework.boot:spring-boot-starter-web")
    implementation("com.fasterxml.jackson.module:jackson-module-kotlin")
    implementation("org.jetbrains.kotlin:kotlin-reflect")
    implementation("org.jetbrains.kotlin:kotlin-stdlib-jdk8")
+   implementation("mysql:mysql-connector-java:8.0.20")
    compileOnly("org.projectlombok:lombok")
    annotationProcessor("org.projectlombok:lombok")
    testImplementation("org.springframework.boot:spring-boot-starter-test")
}

엔티티 만들기

미리 entity 패키지를 작성하십시오.

Demo.kt를 작성합니다.

Demo.kt

package com.example.demo.entity

import javax.persistence.Entity
import javax.persistence.GeneratedValue
import javax.persistence.Id

@Entity
class Demo (
        var name: String? = null,
        @Id
        @GeneratedValue
        var id: Long? = null)

리포지토리 생성

미리 repository 패키지를 작성하십시오.

DemoRepository.kt를 만듭니다.

DemoRepository.kt

package com.example.demo.repository

import com.example.demo.entity.Demo
import org.springframework.data.repository.CrudRepository

interface DemoRepository : CrudRepository<Demo, Long> {
    fun findAllByOrderById(): Iterable<Demo>
}

컨트롤러 수정

DemoController.kt

package com.example.demo.controller

import com.example.demo.entity.Demo
import com.example.demo.repository.DemoRepository
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.http.MediaType
import org.springframework.http.ResponseEntity
import org.springframework.web.bind.annotation.GetMapping
import org.springframework.web.bind.annotation.RequestMapping
import org.springframework.web.bind.annotation.RestController

@RestController
@RequestMapping("/demo")
class DemoController @Autowired constructor(  //修正
        val demoRepository: DemoRepository)   //修正
{                                             //修正   

    @GetMapping("/getAll")
    fun getAll(): ResponseEntity<Iterable<Demo>> {             //修正
        val demos = demoRepository.findAllByOrderById()        //修正  
        return ResponseEntity.ok(demos)                        //修正 
    }

}

브라우저에서 표시

브라우저에서 http://localhost:8080/demo/getAll을 표시합니다

아래와 같이 DB에 등록된 데이터가 반환되었는지 확인합니다.

요약

kotlin + Spring Boot에서 JSON을 Get하는 곳까지했습니다. 뭔가 도움이되면 다행입니다.

참고:
Getting started with Spring Data JPA
Kotlin with Spring Boot 2.0에서 간단한 Rest API 구현