Spring Boot 입문

# Spring Boot 입문 가이드

## 학습 목표
Spring Boot로 Java 웹 애플리케이션을 개발합니다.

## 1. Spring Boot란?
Java 기반 웹 프레임워크입니다.
- 설정 자동화
- 내장 톰캣 서버
- 의존성 관리 간소화
- 프로덕션 레디

## 2. 프로젝트 생성
Spring Initializr:
https://start.spring.io
- Project: Maven 또는 Gradle
- Language: Java
- Dependencies: Spring Web, Spring Data JPA, MySQL Driver

IDE에서 생성:
IntelliJ: New Project > Spring Initializr
VS Code: Spring Boot Extension

## 3. 프로젝트 구조
src/main/java/
com/example/demo/
DemoApplication.java
controller/
service/
repository/
model/
src/main/resources/
application.properties
static/
templates/
pom.xml (Maven) / build.gradle (Gradle)

## 4. 기본 애플리케이션
@SpringBootApplication
public class DemoApplication {
public static void main(String[] args) {
SpringApplication.run(DemoApplication.class, args);
}
}

## 5. REST Controller
@RestController
@RequestMapping("/api")
public class UserController {

@GetMapping("/users")
public List<User> getUsers() {
return userService.findAll();
}

@GetMapping("/users/{id}")
public User getUser(@PathVariable Long id) {
return userService.findById(id);
}

@PostMapping("/users")
public User createUser(@RequestBody User user) {
return userService.save(user);
}

@PutMapping("/users/{id}")
public User updateUser(@PathVariable Long id, @RequestBody User user) {
return userService.update(id, user);
}

@DeleteMapping("/users/{id}")
public void deleteUser(@PathVariable Long id) {
userService.delete(id);
}
}

## 6. Entity
@Entity
@Table(name = "users")
public class User {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;

@Column(nullable = false)
private String name;

@Column(unique = true)
private String email;

@CreationTimestamp
private LocalDateTime createdAt;

// Getters and Setters
}

## 7. Repository
@Repository
public interface UserRepository extends JpaRepository<User, Long> {
List<User> findByName(String name);
Optional<User> findByEmail(String email);
List<User> findByNameContaining(String keyword);

@Query("SELECT u FROM User u WHERE u.createdAt > :date")
List<User> findRecentUsers(@Param("date") LocalDateTime date);
}

## 8. Service
@Service
public class UserService {

@Autowired
private UserRepository userRepository;

public List<User> findAll() {
return userRepository.findAll();
}

public User findById(Long id) {
return userRepository.findById(id)
.orElseThrow(() -> new RuntimeException("User not found"));
}

public User save(User user) {
return userRepository.save(user);
}

@Transactional
public User update(Long id, User userData) {
User user = findById(id);
user.setName(userData.getName());
user.setEmail(userData.getEmail());
return userRepository.save(user);
}

public void delete(Long id) {
userRepository.deleteById(id);
}
}

## 9. application.properties
서버 설정:
server.port=8080

데이터베이스:
spring.datasource.url=jdbc:mysql://localhost:3306/mydb
spring.datasource.username=root
spring.datasource.password=password
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver

JPA:
spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql=true
spring.jpa.properties.hibernate.format_sql=true

## 10. 의존성 주입
생성자 주입 (권장):
@Service
public class UserService {
private final UserRepository userRepository;

public UserService(UserRepository userRepository) {
this.userRepository = userRepository;
}
}

Lombok 사용:
@Service
@RequiredArgsConstructor
public class UserService {
private final UserRepository userRepository;
}

## 11. 예외 처리
@RestControllerAdvice
public class GlobalExceptionHandler {

@ExceptionHandler(RuntimeException.class)
public ResponseEntity<String> handleRuntimeException(RuntimeException e) {
return ResponseEntity.status(HttpStatus.NOT_FOUND).body(e.getMessage());
}

@ExceptionHandler(Exception.class)
public ResponseEntity<String> handleException(Exception e) {
return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).body("Server error");
}
}

## 12. 실행 및 빌드
실행:
./mvnw spring-boot:run
./gradlew bootRun

빌드:
./mvnw clean package
./gradlew build

JAR 실행:
java -jar target/demo-0.0.1-SNAPSHOT.jar
java -jar -Dspring.profiles.active=prod app.jar

## 추천 학습 순서
1. 기본 REST API 작성
2. JPA Entity와 Repository
3. Service 계층 구현
4. 예외 처리
5. 보안 및 배포