Cross-cutting concerns

Common functionality that appears repeatedly "across" multiple modules and layers of a program. Not directly related to business logic, but needed almost everywhere

Solutions

AOP (Aspect-Oriented Programming)

A common solution for cross-cutting concerns

Concept: Extract common functionality into "Aspects" and automatically inject them

Example:


@Before("allServices()")
log();

@Around("allServices()")
auth();

→ Applied automatically without writing code directly

Commonly used in Spring, AspectJ, etc.

Middleware / Interceptor

Most common in web development

Examples: Express / FastAPI / Spring


Request
 → Auth Middleware
 → Logging Middleware
 → Service
 → Response

Example (FastAPI):


@app.middleware("http")
async def log_request(request, call_next):
    ...

Decorator / Wrapper

Commonly used in Python


@log
@auth
def my_func():
    ...

Framework-Level Handling

Most modern frameworks provide built-in solutions:

Spring Security

Django Middleware

NestJS Guard

FastAPI Dependency