Plugin Architecture and Feature Flags

Extensibility without redeploying core code.

Expert14 min read

Read these first

CQRS and Event Sourcing Intro

Why this matters

Plugin registry — detailed pointwise breakdown in the section below.
SPI — detailed pointwise breakdown in the section below.
Feature flags — detailed pointwise breakdown in the section below.
CampusOS rollout — detailed pointwise breakdown in the section below.
Games and architecture patterns signal staff+ depth.

Wrapped component

LoggingDecorator

RetryDecorator

CoreService

Wrap behaviour in layers without subclass explosion.

Overview

Extensibility without redeploying core code. Study each section below in order — every list is interview-ready reference material.

Plugin registry

Points to cover

Definition — what Plugin registry 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

SPI

Points to cover

Definition — what SPI 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

Feature flags

Points to cover

Definition — what Feature flags 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 rollout

Points to cover

Definition — what CampusOS rollout 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

Java

// CampusOS — apply "Plugin registry" on paper first, then in code
public final class PluginAndFeatureFlagsExample {
    // 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.

Plugin registry — review this slice before mock interviews.
SPI — review this slice before mock interviews.
Feature flags — review this slice before mock interviews.
CampusOS rollout — review this slice before mock interviews.

Test yourself

Answer these before moving on — recall is what makes it stick.