leejunkim

Spring's Core Modules

4 min read

The Dependency Structure

Spring Framework Structure

  • Not one library, but a modular platform of many hierarchical components
  • Each module serves a distinct purpose (e.g., IoC, AOP, Web, Data)
  • Knowing the module structure clarifies how Spring works and where specific features reside

Checking the Gradle Dependency Tree

  • Using features in Spring Boot pulls in multiple Spring modules via a dependency tree
  • To view all dependencies across configurations (compile, runtime, test):
./gradlew dependencies
# 특정 Configuration에서 compileClasspath라는 이름의 의존성만 출력
./gradlew dependencies --configuration compileClasspath

Hierarchical Position of Key Modules

  • spring-core
    • Most fundamental Spring module (Foundation for nearly all other Spring modules)
    • Provides utilities: reflection, type conversion, collections, exception handling
    • Reminds me of Java’s Object
    • Key classes: ObjectUtils, Assert, ClassUtils, PropertyEditor
  • spring-beans
    • Core module for DI (Dependency Injection)
    • Handles Bean creation, registration, and injection
    • Powers annotations like @Component, @Bean, and use of ApplicationContext
    • Built on top of spring-core.
  • spring-context
    • Provides full container environment:
      • Bean registration, event publishing, message resolution
    • Core of ApplicationContext implementations
    • Enables: @Configuration, @Autowired, @Value, ApplicationContextAware
    • Backbone for runtime environment in Spring Boot & MVC
    • Depends on: spring-core, spring-beans
  • spring-web
    • The foundational layer for web functionalities, including HTTP request processing, Servlet API, RestTemplate, WebClient, etc.
      • spring-web supports both API server roles (receiving) and API client roles (sending), making it essential for building distributed systems in Spring.
    • Contains core web functionalities that precede the MVC stage.
      • servlet
    • Depends on spring-beans, spring-core.
  • spring-aop
    • Provides AOP-related functionalities (@Aspect, @Before, @After, Proxy-based Interceptors, etc.).
    • Proxy based AOP
    • Essential for implementing Spring’s own transaction and security logic.
  • SpEL
    • Spring사용에 필요한 문법이 담김

Others

  • spring-tx, spring-jdbc
    • 데이터 액세스와 트랜잭션 처리 기능 분리
    • spring-jdbc: JDBC 연동, JdbcTemplate, SQL 예외 처리
      • allows to interact with database
    • spring-tx: 선언적/프로그래밍 방식 트랜잭션 처리, @Transactional 지원
    • ORM 연동(Hibernate, JPA) 시에도 spring-tx가 중간 조정자 역할
      • allows us to interact with a db
Java JDBC API
	↑
Spring JDBC
	↑
Spring Data JPA
ModuleDescription
spring-messagingWebSocket, STOMP 등 메시징 추상화
- 실시간 통신
spring-aspectsAspectJ와 통합할 때 사용하는 보조 모듈
spring-test테스트 지원 (@SpringBootTest, @WebMvcTest 등)
- Mockito 같은 것도 활용을 함

Spring modules have unidirectional dependencies

  • functionalities at a higher level implicitly include more lower-level modules
  • The Arrows (↑) mean “depends on” or “is built on top of”
spring-core
   ↑
spring-beans
   ↑
spring-context
   ↑
spring-web
   ↑
spring-webmvc
  • For instance, while @RestController is defined within spring-webmvc, its functionality requires the combined operation of features from spring-context, spring-beans, and spring-core.
  • There are many many more modules, but these modules form the absolutely essential core and the most common web stack

Core Module Hierarchy

spring-core
   ↑
spring-beans
   ↑
spring-context

Web Module Hierarchy

spring-core
   ↑
spring-web
   ↑
spring-webmvc
  • Like a toolbox, you can pick what you only want to use
  • Spring is like a big toolbox that contains other toolboxes (instead of having all the tools together)

Summary

  • Spring Framework는 단일 라이브러리가 아니라, 기능별 책임을 분리한 다수의 모듈로 구성된 계층형 프레임워크다.
  • Gradle의 의존성 트리를 통해 spring-core부터 spring-webmvc까지의 계층 구조와 의존 흐름을 시각적으로 이해할 수 있으며, 이는 실무에서 문제를 디버깅하거나 설정을 이해하는 데 매우 중요한 기반이 된다.
  • Spring의 기반은 spring-core로부터 시작되며, spring-beans와 spring-context를 거쳐 ApplicationContext 기반의 런타임 환경이 완성된다.
  • 웹 계층에서는 spring-web이 HTTP 기반 기능을 담당하고, spring-webmvc가 MVC 구조를 완성하여 웹 애플리케이션 프레임워크로서의 Spring을 형성한다.
  • spring-aop, spring-jdbc, spring-tx 등의 모듈은 횡단 관심사나 데이터 접근 등의 기능을 선택적으로 확장 가능하게 제공하며, 필요에 따라 Spring 애플리케이션에 유연하게 통합된다.

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