Reactive Programming using Spring Boot and Project Reactor with MongoDB

✅ Your Goals:

Requirement	What It Means	✔ Status
🎯 Interview-Focused	Understand concepts clearly and be able to explain/react during interviews	✔ Valid
👨‍💻 Hands-On & Practical	Build real-world Spring Boot apps using reactive MongoDB	✔ Excellent idea
🧠 Beginner-Friendly	Start from scratch — no assumptions about prior reactive knowledge	✔ Clear goal
🚀 Progressive Mastery	Learn basics, then build toward advanced concepts (Flux, Mono, backpressure, WebFlux)	✔ Smart
💡 Real-World Scenario	Connect concepts to relatable use cases (e.g., booking system, chat app, IoT monitor)	✔ Highly effective

🔹 PHASE 1: Reactive Programming Essentials (Java + Project Reactor)

Get familiar with Mono, Flux, operators, backpressure, and the reactive mindset.

• What is Reactive Programming?

• Push vs Pull / Imperative vs Declarative

• Project Reactor Basics: Mono<T>, Flux<T>

• Key Operators: map(), flatMap(), filter(), zip(), combineLatest(), timeout(), etc.

• Error Handling in Reactive (e.g., onErrorResume, retry)

• Writing small examples like reactive data pipelines.

🔹 PHASE 2: Spring WebFlux Basics

Learn to build REST APIs reactively using Spring Boot and WebFlux.

• Spring Boot Reactive Starter

• @RestController with Mono and Flux

• WebClient (reactive replacement for RestTemplate)

• Creating simple services like:

  • Reactive "Todo API"

  • Reactive "User Service"

🔹 PHASE 3: Reactive MongoDB Integration

Connect your reactive services to a real database — MongoDB.

• Introduction to ReactiveMongoRepository

• Configuring Spring Data MongoDB (Reactive)

• Creating document classes with @Document

• Building real-world example:

  🎯 Real-World App: Reactive Patient Health Tracker

  • Add patients, retrieve vitals, stream live health data updates

  • Use tailable cursors for live data like heart rate/steps

🔹 PHASE 4: Real-Time Streaming and Advanced Concepts

Learn how to stream data to clients in real time using reactive streams.

• Streaming endpoints (SSE, Flux<T> over HTTP)

• WebSocket + Reactive messaging (optional)

• Schedulers, subscribeOn, publishOn

• Backpressure strategies

🔹 PHASE 5: Interview-Focused Deep Dives

Prepare for common technical questions, with confident, hands-on answers.

• Difference between Mono and Flux

• When not to use reactive?

• How does backpressure work?

• How does flatMap() differ from map()?

• Blocking vs non-blocking in Spring WebFlux

• How reactive Mongo driver works

• Integration with WebClient (reactive HTTP)