🌱 Spring Boot Notes

🎯 Purpose

Core Spring Boot patterns for enterprise-style backend projects.

🧠 IoC and DI Essentials

Annotation	Meaning
`@Component`	Generic bean
`@Service`	Service-layer bean
`@Repository`	Persistence-layer bean
`@Controller`	MVC controller
`@RestController`	JSON API controller
`@Configuration`	Bean configuration class
`@Bean`	Registers method return as bean

@Service
public class UserServiceImpl implements UserService {
    private final UserMapper userMapper;

    public UserServiceImpl(UserMapper userMapper) {
        this.userMapper = userMapper;
    }
}

🌐 Web MVC Annotations

Annotation	Usage
`@RequestMapping`	Base path mapping
`@GetMapping`	HTTP GET
`@PostMapping`	HTTP POST
`@PutMapping`	HTTP PUT
`@DeleteMapping`	HTTP DELETE
`@PathVariable`	Value from URL path
`@RequestParam`	Query parameter
`@RequestBody`	JSON request body

@RestController
@RequestMapping("/users")
public class UserController {

    @GetMapping
    public ApiResponse<List<UserResponse>> getAll() { ... }

    @GetMapping("/{id}")
    public ApiResponse<UserResponse> getById(@PathVariable Long id) { ... }

    @PostMapping
    public ApiResponse<Void> create(@RequestBody UserRequest req) { ... }
}

🔄 Transactions

@Service
public class UserServiceImpl {

    @Transactional
    public void createUser(UserRequest req) {
        userMapper.insert(req);
        auditMapper.log(req);
    }

    @Transactional(readOnly = true)
    public List<UserResponse> getAll() {
        return userMapper.selectAll();
    }
}

🏗️ Recommended Layer Structure

Controller -> Service -> Mapper -> Database

Layer	Role
`controller/`	Handles HTTP request/response
`service/`	Business logic and transaction boundary
`mapper/`	SQL mapping via MyBatis
`dto/`	Request/response schema
`model/`	Table-aligned domain object
`config/`	Spring config classes
`common/`	Shared response/error utilities

⚙️ `application.properties` baseline

server.port=8080

spring.datasource.url=jdbc:postgresql://localhost:5432/postgres
spring.datasource.username=postgres
spring.datasource.password=your_password
spring.datasource.driver-class-name=org.postgresql.Driver

mybatis.mapper-locations=classpath:mapper/**/*.xml
mybatis.type-aliases-package=com.yourpackage.model
mybatis.configuration.map-underscore-to-camel-case=true

logging.level.com.yourpackage.mapper=DEBUG

📦 Unified API Response Pattern

public class ApiResponse<T> {
    private String resultCd;
    private String resultMsg;
    private T data;

    public static <T> ApiResponse<T> success(T data) {
        return new ApiResponse<>("M0000", "Success", data);
    }

    public static <T> ApiResponse<T> error(String msg) {
        return new ApiResponse<>("E9999", msg, null);
    }
}

🔐 CORS Example

@Configuration
public class CorsConfig implements WebMvcConfigurer {
    @Override
    public void addCorsMappings(CorsRegistry registry) {
        registry.addMapping("/**")
                .allowedOrigins("http://localhost:3000")
                .allowedMethods("GET", "POST", "PUT", "DELETE");
    }
}

✅ Quick Practice Rules

Prefer constructor injection.
Keep controller thin; place logic in service.
Keep mapper SQL focused and explicit.
Return a consistent API response shape.