Java Class Refactoring Assistant

Java Class Refactoring Assistant

Overview

Intelligently refactor complex Java classes following Clean Architecture, DDD patterns, and Spring Boot best practices.

Provides intelligent refactoring for complex Java classes with architectural analysis and Spring Boot patterns. Use when refactoring large or complex Java classes.

Usage

/devkit.java.refactor-class $ARGUMENTS

Arguments

Current Context

• Current Git Branch: !git branch --show-current
• Git Status: !git status --porcelain
• Recent Commits: !git log --oneline -5
• Test Coverage: !find . -name "*Test.java" -type f | wc -l test files found

Execution Instructions

Agent Selection: To execute this task, use the following agent with fallback:

• Primary: developer-kit-java:java-refactor-expert
• If not available: Use developer-kit-java:java-refactor-expert or fallback to general-purpose agent with spring-boot-crud-patterns skill

Refactoring Configuration

Analyzing: $ARGUMENTS

Parameters:

• $1 - Class file path (required): Path to Java class to refactor
• $2 - Refactoring scope (optional):
  • cleanup - Code cleanup and style improvements (default)
  • architecture - Architectural pattern improvements
  • performance - Performance optimizations
  • security - Security enhancements
  • testing - Testability improvements
  • comprehensive - All improvements (full refactor)
• $3 - Options (optional): dry-run, backup, validate-only

Pre-Refactoring Analysis

1. Class Identification and Context

IF "$1" is empty OR not provided THEN Analyze the most complex class in the codebase automatically ELSE Analyze specific class: $1 ENDIF

2. Architecture Pattern Detection

Expected Clean Architecture Structure:
feature/
├── domain/
│   ├── model/           # Domain entities (Spring-free)
│   ├── repository/      # Domain ports (interfaces)
│   └── service/         # Domain services
├── application/
│   ├── service/         # Use cases (@Service beans)
│   └── dto/             # Immutable DTOs/records
├── presentation/
│   └── rest/            # Controllers and mappers
└── infrastructure/
    └── persistence/     # JPA adapters

Refactoring Strategy by Scope

Cleanup Refactoring ($2 = "cleanup")

• Code Style: Apply consistent formatting, naming conventions
• Dead Code: Remove unused imports, methods, variables
• Complexity: Simplify complex methods (< 10 cyclomatic complexity)
• Documentation: Add missing JavaDoc and inline comments
• Immutability: Convert to immutable structures where possible

Architecture Refactoring ($2 = "architecture")

• Layer Separation: Ensure proper dependency direction
• DDD Patterns: Apply aggregates, value objects, domain events
• Spring Patterns: Constructor injection, proper bean scoping
• Repository Pattern: Domain interfaces + infrastructure adapters
• DTO Pattern: Replace JPA entities with records in APIs

Performance Refactoring ($2 = "performance")

• Database Queries: Optimize JPA queries, eliminate N+1 problems
• Caching: Add @Cacheable, @CachePut, @CacheEvict where appropriate
• Async Processing: Convert blocking operations to @Async
• Memory Management: Identify and fix memory leaks
• Algorithm Optimization: Improve computational complexity

Security Refactoring ($2 = "security")

• Input Validation: Add Jakarta Bean Validation
• Authentication: Ensure proper @PreAuthorize usage
• Data Exposure: Prevent sensitive data leakage in DTOs
• SQL Injection: Verify safe JPA usage
• XSS Prevention: Input sanitization and output encoding

Testing Refactoring ($2 = "testing")

• Testability: Extract dependencies for better mocking
• Test Coverage: Add missing unit/integration tests
• Test Structure: Apply AAA pattern (Arrange, Act, Assert)
• Mocking: Proper Mockito usage without static mocks
• Testcontainers: Real database testing for persistence layer

Refactoring Process

Phase 1: Analysis and Planning

1. Read and analyze target class for current patterns and violations
2. Identify dependencies and usage patterns across codebase
3. Assess test coverage - if missing, create tests BEFORE refactoring
4. Create refactoring plan based on selected scope
5. Backup strategy - create branch if not dry-run

Phase 2: Safety Checks

# Run existing tests
./gradlew test || mvn test

# Create backup branch if not dry-run
if [ "$3" != "dry-run" ]; then
  git checkout -b refactor/$(basename "$1" .java)-$(date +%Y%m%d-%H%M%S)
fi

Phase 3: Incremental Refactoring

For each refactoring step:

1. Make small, focused change
2. Run tests to verify no regressions
3. Commit change with descriptive message
4. Document improvement and rationale

Phase 4: Validation

# Full test suite
./gradlew test || mvn test

# Static analysis
./gradlew spotbugsMain || ./gradlew checkstyleMain

# Performance validation
./gradlew bench || echo "No performance tests configured"

Common Refactoring Patterns

Extract Method/Service

// Before: Complex method doing too much
@Service
@RequiredArgsConstructor
public class OrderService {
    public OrderDto createOrder(CreateOrderRequest request) {
        // Validation logic (20+ lines)
        // Business logic (30+ lines)
        // Notification logic (15+ lines)
        // Audit logic (10+ lines)
    }
}

// After: Extracted responsibilities
@Service
@RequiredArgsConstructor
public class OrderService {
    private final OrderValidator validator;
    private final OrderProcessor processor;
    private final NotificationService notificationService;
    private final AuditService auditService;

    public OrderDto createOrder(CreateOrderRequest request) {
        validator.validate(request);
        var order = processor.process(request);
        notificationService.sendOrderCreated(order);
        auditService.logOrderCreation(order);
        return order;
    }
}

Replace with Record/Value Object

// Before: Mutable entity exposed
public class UserDto {
    private String name;
    private String email;
    // getters/setters
}

// After: Immutable record
public record UserDto(String id, String name, String email, Instant createdAt) {
}

Apply Repository Pattern

// Domain port (interface)
public interface UserRepository {
    User save(User user);

    Optional<User> findById(UserId id);

    List<User> findByEmail(String email);
}

// Infrastructure adapter
@Repository
@RequiredArgsConstructor
public class UserRepositoryAdapter implements UserRepository {
    private final UserJpaRepository jpaRepository;
    private final UserMapper mapper;

    @Override
    public User save(User user) {
        var entity = mapper.toEntity(user);
        var saved = jpaRepository.save(entity);
        return mapper.toDomain(saved);
    }
}

Add Spring Security

// Before: No authorization
@PreAuthorize("hasRole('ADMIN')")
@GetMapping("/api/admin/users")
public ResponseEntity<List<UserDto>> getAllUsers() {
    // Implementation
}

// After: Method-level security
@PreAuthorize("hasRole('ADMIN') or hasAuthority('USERS_READ')")
@GetMapping("/api/admin/users")
public ResponseEntity<List<UserDto>> getAllUsers() {
    // Implementation
}

Output and Reporting

Refactoring Summary

• Files Modified: List of changed files with line counts
• Patterns Applied: Specific patterns and improvements made
• Test Impact: New tests added, existing tests updated
• Performance Changes: Before/after metrics if available

Quality Metrics

• Cyclomatic Complexity: Reduced from X to Y
• Lines of Code: Reduced by X%
• Test Coverage: Increased from X% to Y%
• Dependencies: Reduced coupling between components

Next Steps

1. Review changes with team
2. Run integration tests in staging environment
3. Monitor performance after deployment
4. Update documentation for changed APIs

Integration with Skills

This command works best with these skills:

• spring-boot-crud-patterns: For CRUD refactoring
• spring-boot-test-patterns: For test improvements
• spring-boot-rest-api-standards: For API refactoring
• unit-test-service-layer: For service layer testing

Safety and Validation

• Always preserve external behavior while improving internal structure
• Maintain backward compatibility for public APIs
• Create comprehensive tests before refactoring critical paths
• Use feature flags for large, risky refactoring
• Monitor production metrics after deployment

Examples

# Cleanup and style improvements
/developer-kit-java:devkit.java.refactor-class src/main/java/com/example/service/UserService.java cleanup

# Full architectural refactoring with backup
/developer-kit-java:devkit.java.refactor-class src/main/java/com/example/service/OrderService.java comprehensive backup

# Performance optimization only
/developer-kit-java:devkit.java.refactor-class src/main/java/com/example/repository/ProductRepository.java performance

# Dry run to see what would change
/developer-kit-java:devkit.java.refactor-class src/main/java/com/example/controller/UserController.java architecture dry-run

# Automatic complex class detection
/developer-kit-java:devkit.java.refactor-class