Why this matters
- Handler interface — detailed pointwise breakdown in the section below.
- Auth then rate-limit — detailed pointwise breakdown in the section below.
- Ordering — detailed pointwise breakdown in the section below.
- CampusOS API gateway — detailed pointwise breakdown in the section below.
- Production Java structure interviewers expect in backend LLD.
Request
Auth
Validate
Handler
Overview
Compose cross-cutting concerns as a pipeline. Study each section below in order — every list is interview-ready reference material.
Handler interface
Points to cover
- Definition — what Handler interface means in one clear sentence
- When to use — the force or smell that triggers this concept
- CampusOS example — where this appears in parking, booking, or library modules
- How to explain — pointwise bullets you can say aloud in an interview
- Common mistake — what weak candidates do instead
- Refactor move — one concrete change that improves the design
Auth then rate-limit
Points to cover
- Definition — what Auth then rate-limit means in one clear sentence
- When to use — the force or smell that triggers this concept
- CampusOS example — where this appears in parking, booking, or library modules
- How to explain — pointwise bullets you can say aloud in an interview
- Common mistake — what weak candidates do instead
- Refactor move — one concrete change that improves the design
Ordering
Points to cover
- Definition — what Ordering means in one clear sentence
- When to use — the force or smell that triggers this concept
- CampusOS example — where this appears in parking, booking, or library modules
- How to explain — pointwise bullets you can say aloud in an interview
- Common mistake — what weak candidates do instead
- Refactor move — one concrete change that improves the design
CampusOS API gateway
Points to cover
- Definition — what CampusOS API gateway means in one clear sentence
- When to use — the force or smell that triggers this concept
- CampusOS example — where this appears in parking, booking, or library modules
- How to explain — pointwise bullets you can say aloud in an interview
- Common mistake — what weak candidates do instead
- Refactor move — one concrete change that improves the design
// CampusOS — apply "Handler interface" on paper first, then in code
public final class MiddlewareChainExample {
// 1. Name entities from the problem statement
// 2. Draw relationships before writing methods
// 3. Introduce patterns only when a force appears
}
Quick recall
Everything you need if you only revisit this box.
- Handler interface — review this slice before mock interviews.
- Auth then rate-limit — review this slice before mock interviews.
- Ordering — review this slice before mock interviews.
- CampusOS API gateway — review this slice before mock interviews.
Test yourself
Answer these before moving on — recall is what makes it stick.