java-spring-arch

name	java-spring-arch
description	Architecture reference for Java + Spring Boot 4.0 projects — Controller/Service/Repository layer responsibilities, @Transactional strategy (readOnly optimization, N+1 prevention), ExpectedException usage, and Entity↔DTO conversion patterns.

Java + Spring Boot Architecture Guide

Layer Structure

Controller

• Role: Request validation, DTO conversion, HTTP response
• Annotations: @RestController, @RequestMapping
• Validation: @Valid, @Validated
• Response: Use CommonApiResponse wrapper

Service

• Role: Business logic, transaction management
• Pattern: interface + implementation
• Transaction:
  • Read: @Transactional(readOnly = true)
  • Write: @Transactional
• Dependencies: Inject Repository via constructor injection

Repository

• Role: Data access
• JPA: Extend JpaRepository
• Avoid N+1: Fetch Join, @EntityGraph

Transaction Strategy

Read-only Optimization

@Transactional(readOnly = true)
public List<StudentResDto> findStudents() {
    return repository.findAll().stream()
        .map(StudentResDto::from)
        .toList();
}

N+1 Problem Resolution

// ❌ N+1 occurs
repository.findAll(); // 1 query
entity.getRelatedEntities(); // N queries

// ✅ Fetch Join
@Query("SELECT e FROM Entity e JOIN FETCH e.relatedEntities")
List<Entity> findAllWithRelated();

Exception Handling

throw new ExpectedException("학생을 찾을 수 없습니다.", HttpStatus.NOT_FOUND);

DTO Conversion Pattern

// Entity → ResDto (static factory)
public static StudentResDto from(Student student) {
    return new StudentResDto(student.getId(), student.getName());
}