2nd/10_Wiki/Topics/Architecture/Aspect-Oriented Programming (AOP).md

---
id: wiki-2026-0508-aspect-oriented-programming-aop
title: Aspect Oriented Programming (AOP)
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [AOP, Aspect Programming, Cross-cutting Concerns]
duplicate_of: none
source_trust_level: A
confidence_score: 0.9
verification_status: applied
tags: [architecture, paradigm, spring, decorator]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: Java / TypeScript / Python
  framework: Spring AOP / AspectJ / NestJS
---

# Aspect-Oriented Programming (AOP)

## 매 한 줄
> **"매 cross-cutting concern을 separate aspect로 modularize."**. 1997년 Gregor Kiczales (Xerox PARC) 의 AspectJ 가 시초. 2026 현재 Spring AOP 6.x, NestJS interceptor, Python decorator 가 주류 — logging/transaction/security 같이 매 객체 가로지르는 logic을 매 한 곳에 모음.

## 매 핵심

### 매 용어
- **Aspect**: 매 cross-cutting concern 의 modular 단위 (e.g. `LoggingAspect`).
- **Join Point**: 매 program execution 의 한 지점 (method call, field access).
- **Pointcut**: 매 join point 의 selection expression.
- **Advice**: 매 pointcut 매칭 시 실행할 code (`@Before`, `@After`, `@Around`).
- **Weaving**: 매 aspect 와 base code 결합 — compile-time / load-time / runtime.

### 매 cross-cutting concerns
- Logging / tracing
- Transaction management
- Security / authorization
- Caching
- Performance monitoring
- Error handling / retry
- Audit trail

### 매 응용
1. Spring `@Transactional` — DB transaction 자동 commit/rollback.
2. NestJS `@UseInterceptors` — request/response transform.
3. Python `@functools.lru_cache` — pure caching aspect.
4. OpenTelemetry auto-instrumentation — runtime byte-code weaving.

## 💻 패턴

### Spring AOP — @Around aspect
```java
@Aspect
@Component
public class LoggingAspect {

    @Around("execution(* com.example.service.*.*(..))")
    public Object logExecutionTime(ProceedingJoinPoint pjp) throws Throwable {
        long start = System.currentTimeMillis();
        try {
            Object result = pjp.proceed();
            long elapsed = System.currentTimeMillis() - start;
            log.info("{} took {} ms", pjp.getSignature(), elapsed);
            return result;
        } catch (Throwable t) {
            log.error("{} threw {}", pjp.getSignature(), t.getMessage());
            throw t;
        }
    }
}
```

### Spring — @Transactional declarative TX
```java
@Service
public class OrderService {

    @Transactional(rollbackFor = Exception.class, isolation = Isolation.READ_COMMITTED)
    public Order placeOrder(OrderRequest req) {
        Order order = orderRepo.save(new Order(req));
        inventoryRepo.decrement(req.getItems());
        // Any RuntimeException → automatic rollback via AOP proxy
        return order;
    }
}
```

### NestJS — Interceptor (AOP-style)
```typescript
import { CallHandler, ExecutionContext, Injectable, NestInterceptor } from '@nestjs/common';
import { Observable, tap } from 'rxjs';

@Injectable()
export class TimingInterceptor implements NestInterceptor {
  intercept(ctx: ExecutionContext, next: CallHandler): Observable<unknown> {
    const start = Date.now();
    return next.handle().pipe(
      tap(() => console.log(`${ctx.getHandler().name} took ${Date.now() - start}ms`)),
    );
  }
}

@Controller('orders')
@UseInterceptors(TimingInterceptor)
export class OrdersController { /* ... */ }
```

### Python — Decorator as aspect
```python
import functools, time, logging

def timed(func):
    @functools.wraps(func)
    def wrapper(*args, **kwargs):
        start = time.perf_counter()
        try:
            return func(*args, **kwargs)
        finally:
            elapsed = time.perf_counter() - start
            logging.info(f"{func.__name__} took {elapsed*1000:.1f}ms")
    return wrapper

@timed
def expensive_calc(n: int) -> int:
    return sum(i * i for i in range(n))
```

### Python — Class-based retry aspect
```python
def retry(times: int = 3, on: tuple = (Exception,)):
    def decorator(func):
        @functools.wraps(func)
        def wrapper(*args, **kwargs):
            last = None
            for attempt in range(times):
                try:
                    return func(*args, **kwargs)
                except on as e:
                    last = e
                    time.sleep(2 ** attempt)
            raise last
        return wrapper
    return decorator

@retry(times=5, on=(httpx.HTTPError,))
def fetch_remote(url: str) -> dict:
    return httpx.get(url).json()
```

### AspectJ pointcut DSL
```java
@Pointcut("execution(public * com.example.repo.*.find*(..))")
public void anyFinder() {}

@Pointcut("@annotation(com.example.Audited)")
public void auditedMethod() {}

@Before("anyFinder() && auditedMethod()")
public void audit(JoinPoint jp) {
    auditService.log(jp.getSignature().toShortString(), Instant.now());
}
```

### TypeScript — method decorator
```typescript
function Cached(ttlMs: number): MethodDecorator {
  const cache = new Map<string, { value: unknown; exp: number }>();
  return (_t, _k, desc: PropertyDescriptor) => {
    const original = desc.value;
    desc.value = function (...args: unknown[]) {
      const key = JSON.stringify(args);
      const entry = cache.get(key);
      if (entry && entry.exp > Date.now()) return entry.value;
      const value = original.apply(this, args);
      cache.set(key, { value, exp: Date.now() + ttlMs });
      return value;
    };
  };
}

class Pricing {
  @Cached(60_000)
  fetchRate(currency: string) { /* ... */ }
}
```

## 매 결정 기준
| 상황 | Approach |
|---|---|
| Java enterprise, declarative TX | Spring AOP (proxy-based) |
| 매 method 매칭 + field access weaving | AspectJ (compile/load-time) |
| Node.js HTTP layer | NestJS Interceptor / Guard |
| Python script / function-level | Decorator |
| Cross-language tracing | OpenTelemetry auto-instrumentation |

**기본값**: framework-native (Spring AOP / NestJS interceptor / decorator). 매 raw AspectJ 는 매 매우 specific 한 경우만.

## 🔗 Graph
- 부모: [[Object-Oriented-Programming]] · [[Software-Architecture]]
- 변형: [[Middleware]]
- 응용: [[Spring Framework]] · [[NestJS]] · [[OpenTelemetry]]
- Adjacent: [[Dependency_Injection_(DI)|Dependency-Injection]] · [[Cross-Cutting Concerns]]

## 🤖 LLM 활용
**언제**: cross-cutting concern (logging/TX/security/caching) 이 매 여러 service 에 반복, declarative style 선호, framework 가 AOP 지원.
**언제 X**: 매 한두 곳만 쓰는 logic (직접 호출이 명확), 매 magic 회피 culture, 매 debug 어려움 감수 못할 때.

## ❌ 안티패턴
- **Aspect 안 business logic**: 매 aspect 는 매 cross-cutting 만 — 매 domain rule 넣지 X.
- **너무 broad pointcut**: `execution(* *.*(..))` — 매 unintended weaving.
- **Self-invocation 의 proxy bypass**: 매 같은 class 안 method call 은 매 proxy 통과 안 함 (Spring).
- **Order 의존**: 매 multiple aspect 매 ordering 명시 X 면 매 비결정적.
- **Aspect explosion**: 매 100+ aspect → 매 control flow 추적 불가.

## 🧪 검증 / 중복
- Verified (Spring Framework 6.x docs, AspectJ programming guide, NestJS docs).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — AOP full content with Spring/NestJS/Python patterns |