🍃 Spring Boot 완전 가이드

@RestController
@RequestMapping("/api/v1/users")
@RequiredArgsConstructor
public class UserController {
    private final UserService userService;

    @GetMapping
    public Page<UserResponse> list(@RequestParam(defaultValue="0") int page) {
        return userService.findAll(PageRequest.of(page, 20));
    }

    @PostMapping
    @ResponseStatus(HttpStatus.CREATED)
    public UserResponse create(@Valid @RequestBody CreateUserRequest req) {
        return userService.create(req);
    }
}

// 권장: 생성자 주입 — final로 불변성 보장, 테스트 시 mock 주입이 쉬움
@Service
@RequiredArgsConstructor   // Lombok이 final 필드를 받는 생성자를 자동 생성
public class OrderService {
    private final PaymentClient paymentClient;
    private final OrderRepository orderRepository;

    public Order placeOrder(OrderRequest req) {
        paymentClient.charge(req.amount());
        return orderRepository.save(Order.from(req));
    }
}

// 비권장: 필드 주입 — final 불가, 테스트 시 리플렉션 없이는 mock 주입 불가
@Service
public class LegacyOrderService {
    @Autowired
    private PaymentClient paymentClient;
}

@Entity @Table(name="users")
@Getter @Builder @NoArgsConstructor @AllArgsConstructor
public class User {
    @Id @GeneratedValue(strategy=IDENTITY) private Long id;
    @Column(nullable=false)               private String name;
    @Column(nullable=false, unique=true)  private String email;
    @CreationTimestamp private LocalDateTime createdAt;
}

public interface UserRepository extends JpaRepository<User, Long> {
    Optional<User> findByEmail(String email);
    boolean existsByEmail(String email);
}

@RestControllerAdvice
public class GlobalExceptionHandler {

    @ExceptionHandler(EntityNotFoundException.class)
    public ResponseEntity<ErrorResponse> handleNotFound(EntityNotFoundException ex) {
        return ResponseEntity.status(HttpStatus.NOT_FOUND)
            .body(new ErrorResponse("NOT_FOUND", ex.getMessage()));
    }

    @ExceptionHandler(MethodArgumentNotValidException.class)
    public ResponseEntity<ErrorResponse> handleValidation(MethodArgumentNotValidException ex) {
        String message = ex.getBindingResult().getFieldErrors().stream()
            .map(err -> err.getField() + ": " + err.getDefaultMessage())
            .collect(Collectors.joining(", "));
        return ResponseEntity.badRequest().body(new ErrorResponse("VALIDATION_ERROR", message));
    }

    @ExceptionHandler(Exception.class)
    public ResponseEntity<ErrorResponse> handleUnexpected(Exception ex) {
        log.error("Unhandled exception", ex);   // 원인 파악을 위해 반드시 로그에 스택트레이스 남기기
        return ResponseEntity.internalServerError()
            .body(new ErrorResponse("INTERNAL_ERROR", "일시적인 오류가 발생했습니다"));
    }
}

record ErrorResponse(String code, String message) {}

@Configuration
@EnableWebSecurity
@RequiredArgsConstructor
public class SecurityConfig {
    private final JwtAuthFilter jwtAuthFilter;

    @Bean
    public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
        return http
            .csrf(AbstractHttpConfigurer::disable)   // stateless API는 CSRF 토큰 불필요
            .sessionManagement(s -> s.sessionCreationPolicy(SessionCreationPolicy.STATELESS))
            .authorizeHttpRequests(auth -> auth
                .requestMatchers("/api/login", "/api/signup").permitAll()
                .anyRequest().authenticated())
            .addFilterBefore(jwtAuthFilter, UsernamePasswordAuthenticationFilter.class)
            .build();
    }

    @Bean
    public PasswordEncoder passwordEncoder() {
        return new BCryptPasswordEncoder();
    }
}

@WebMvcTest(OrderController.class)
class OrderControllerTest {
    @Autowired MockMvc mockMvc;
    @MockBean OrderService orderService;

    @Test
    void 주문_생성_성공() throws Exception {
        given(orderService.placeOrder(any())).willReturn(new Order(1L, 10000));

        mockMvc.perform(post("/api/v1/orders")
                .contentType(MediaType.APPLICATION_JSON)
                .content("""
                    {"productId": 1, "amount": 10000}
                """))
            .andExpect(status().isCreated())
            .andExpect(jsonPath("$.id").value(1));
    }

    @Test
    void 검증_실패시_400() throws Exception {
        mockMvc.perform(post("/api/v1/orders")
                .contentType(MediaType.APPLICATION_JSON)
                .content("{}"))
            .andExpect(status().isBadRequest());
    }
}

FROM eclipse-temurin:21-jdk-alpine AS builder
WORKDIR /app
COPY gradlew build.gradle.kts settings.gradle.kts ./
COPY gradle ./gradle
RUN ./gradlew dependencies --no-daemon
COPY src ./src
RUN ./gradlew bootJar --no-daemon

FROM eclipse-temurin:21-jre-alpine
WORKDIR /app
COPY --from=builder /app/build/libs/*.jar app.jar
USER nobody
EXPOSE 8080
ENTRYPOINT ["java","-jar","app.jar"]