Java Spring Boot | REST API 서버 만들기

· 24분 읽기 · 수정 고급 튜토리얼
Java Spring Boot | REST API 서버 만들기

이 글의 핵심

Java Spring Boot에 대한 실전 가이드입니다. REST API 서버 만들기 등을 예제와 함께 상세히 설명합니다.

들어가며

Spring Boot는 설정을 줄이고 관례에 맞춘 뼈대를 빠르게 올리는 데 유리합니다. 컨트롤러·서비스·리포지토리를 설계도(클래스)에 나누어 두고, 의존성 주입으로 조립하는 방식이 일반적입니다.

1. Spring Boot 프로젝트 설정

프로젝트 생성

Spring Initializr에서:

  • Project: Maven
  • Language: Java
  • Spring Boot: 3.x
  • Dependencies: Spring Web, Spring Data JPA, H2 Database

Application.java

package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}

application.properties

server.port=8080
spring.datasource.url=jdbc:h2:mem:testdb
spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql=true

2. REST Controller

UserController

package com.example.demo.controller;

import com.example.demo.model.User;
import com.example.demo.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;

import java.util.List;

@RestController
@RequestMapping("/api/users")
public class UserController {
    
    @Autowired
    private UserService userService;
    
    @GetMapping
    public List<User> getUsers() {
        return userService.findAll();
    }
    
    @GetMapping("/{id}")
    public ResponseEntity<User> getUser(@PathVariable Long id) {
        User user = userService.findById(id);
        if (user != null) {
            return ResponseEntity.ok(user);
        } else {
            return ResponseEntity.notFound().build();
        }
    }
    
    @PostMapping
    public ResponseEntity<User> createUser(@RequestBody User user) {
        User saved = userService.save(user);
        return ResponseEntity.status(HttpStatus.CREATED).body(saved);
    }
    
    @PutMapping("/{id}")
    public ResponseEntity<User> updateUser(
            @PathVariable Long id,
            @RequestBody User user) {
        User updated = userService.update(id, user);
        if (updated != null) {
            return ResponseEntity.ok(updated);
        } else {
            return ResponseEntity.notFound().build();
        }
    }
    
    @DeleteMapping("/{id}")
    public ResponseEntity<Void> deleteUser(@PathVariable Long id) {
        boolean deleted = userService.delete(id);
        if (deleted) {
            return ResponseEntity.noContent().build();
        } else {
            return ResponseEntity.notFound().build();
        }
    }
}

3. JPA Entity

User 엔티티

package com.example.demo.model;

import jakarta.persistence.*;

@Entity
@Table(name = "users")
public class User {
    
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    
    @Column(nullable = false)
    private String name;
    
    @Column(nullable = false, unique = true)
    private String email;
    
    private Integer age;
    
    public User() {}
    
    public User(String name, String email, Integer age) {
        this.name = name;
        this.email = email;
        this.age = age;
    }
    
    // Getters
    public Long getId() { return id; }
    public String getName() { return name; }
    public String getEmail() { return email; }
    public Integer getAge() { return age; }
    
    // Setters
    public void setId(Long id) { this.id = id; }
    public void setName(String name) { this.name = name; }
    public void setEmail(String email) { this.email = email; }
    public void setAge(Integer age) { this.age = age; }
}

4. Repository

UserRepository

package com.example.demo.repository;

import com.example.demo.model.User;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

import java.util.List;

@Repository
public interface UserRepository extends JpaRepository<User, Long> {
    
    List<User> findByName(String name);
    
    User findByEmail(String email);
    
    List<User> findByAgeGreaterThan(Integer age);
}

5. Service

UserService

package com.example.demo.service;

import com.example.demo.model.User;
import com.example.demo.repository.UserRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.List;

@Service
public class UserService {
    
    @Autowired
    private UserRepository userRepository;
    
    public List<User> findAll() {
        return userRepository.findAll();
    }
    
    public User findById(Long id) {
        return userRepository.findById(id).orElse(null);
    }
    
    public User save(User user) {
        return userRepository.save(user);
    }
    
    public User update(Long id, User user) {
        User existing = findById(id);
        if (existing != null) {
            existing.setName(user.getName());
            existing.setEmail(user.getEmail());
            existing.setAge(user.getAge());
            return userRepository.save(existing);
        }
        return null;
    }
    
    public boolean delete(Long id) {
        if (userRepository.existsById(id)) {
            userRepository.deleteById(id);
            return true;
        }
        return false;
    }
}

6. 의존성 주입 (DI)

생성자 주입 (권장)

@Service
public class UserService {
    
    private final UserRepository userRepository;
    
    public UserService(UserRepository userRepository) {
        this.userRepository = userRepository;
    }
}

필드 주입

@Service
public class UserService {
    
    @Autowired
    private UserRepository userRepository;
}

7. 실전 예제

예제: Todo API

// TodoController.java
@RestController
@RequestMapping("/api/todos")
public class TodoController {
    
    private final TodoService todoService;
    
    public TodoController(TodoService todoService) {
        this.todoService = todoService;
    }
    
    @GetMapping
    public List<Todo> getTodos() {
        return todoService.findAll();
    }
    
    @PostMapping
    public ResponseEntity<Todo> createTodo(@RequestBody Todo todo) {
        Todo saved = todoService.save(todo);
        return ResponseEntity.status(HttpStatus.CREATED).body(saved);
    }
    
    @PutMapping("/{id}/toggle")
    public ResponseEntity<Todo> toggleTodo(@PathVariable Long id) {
        Todo updated = todoService.toggle(id);
        if (updated != null) {
            return ResponseEntity.ok(updated);
        } else {
            return ResponseEntity.notFound().build();
        }
    }
}

// Todo.java
@Entity
public class Todo {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    
    private String title;
    private boolean completed;
    
    // Constructors, Getters, Setters
}

// TodoService.java
@Service
public class TodoService {
    
    private final TodoRepository todoRepository;
    
    public TodoService(TodoRepository todoRepository) {
        this.todoRepository = todoRepository;
    }
    
    public List<Todo> findAll() {
        return todoRepository.findAll();
    }
    
    public Todo save(Todo todo) {
        return todoRepository.save(todo);
    }
    
    public Todo toggle(Long id) {
        Todo todo = todoRepository.findById(id).orElse(null);
        if (todo != null) {
            todo.setCompleted(!todo.isCompleted());
            return todoRepository.save(todo);
        }
        return null;
    }
}

// TodoRepository.java
@Repository
public interface TodoRepository extends JpaRepository<Todo, Long> {
    List<Todo> findByCompleted(boolean completed);
}

정리

핵심 요약

  1. Spring Boot: 자동 설정, 빠른 개발
  2. @RestController: REST API 엔드포인트
  3. JPA: 객체 관계 매핑 (ORM)
  4. 의존성 주입: @Autowired, 생성자 주입
  5. Repository: 데이터 접근 계층

다음 단계

  • Java 멀티스레딩
  • Kotlin Spring Boot
  • Java 예외 처리

관련 글

  • Kotlin Spring Boot | REST API 서버 만들기
  • C++ HTTP 클라이언트 완벽 가이드 | REST API 호출·연결 풀·타임아웃·프로덕션 패턴
  • C++ JSON 파싱 완벽 가이드 | nlohmann·RapidJSON·커스텀 타입·에러 처리·프로덕션 패턴
  • C++ REST API 클라이언트 완벽 가이드 | CRUD·인증·에러 처리·프로덕션 패턴 [#21-3]
  • [Go 2주 완성 #08] Day 14: 실전 미니 프로젝트 - REST API 서버 구축