Spring Boot WebFlux Complete Flow | Netty Event Loop Explained ! | Reactive Programming

Build high-throughput, non-blocking APIs with confidence. In this deep dive, we go under the hood of Spring Boot WebFlux + Netty to see exactly how requests are accepted, converted to events, queued, offloaded, and returned—all with reactive backpressure and event loops instead of Tomcat’s thread-per-request model.

You’ll learn why WebFlux on Netty scales to thousands of concurrent connections with fewer threads, how channels, event loop groups (boss vs worker), handler mapping/adapter, and callbacks fit together, and how to read Reactor Netty logs to prove what’s happening at runtime.

What you’ll master

Netty vs Tomcat (Blocking vs Non-Blocking): A side-by-side mental model for capacity, latency, and scalability.

Complete Request Flow: From client request → channel → event creation → Event Loop Task Queue (FIFO) → response.

Event Loop, Demystified: How a single worker thread cycles through many requests without getting stuck.

True Non-Blocking I/O: Offloading IO-intensive work (DB/remote calls) to a separate pool while the loop keeps serving others.

Channels & Callbacks: Ensuring the right response gets back to the right client after offloading completes.

Massive Concurrency: How Spring Boot derives the number of event loops from CPU cores for effortless scaling.

This is essential knowledge for anyone building fast, resilient microservices in 2025,2026 and beyond.

Video Timestamps
Use these chapters to navigate the complete WebFlux flow and Netty internals:

00:00 – Tomcat vs Netty: Thread-Per-Request vs Event Loop
02:25 – What is an Event Loop? (Single-Threaded “Hero”)
05:03 – What is a Channel? (Client–Server connection)
10:15 – Channel Registration with the Event Loop
13:22 – Processing Requests (FIFO Task Queue)
20:54 – Handling Blocking Requests (Offloading to Pool)
29:39 – How Many Event Loops? (CPU core logic)
31:17 – EventLoopGroup: Boss vs Worker threads
40:20 – REST app with Spring MVC – Producer (blocking demo)
44:09 – Analyzing Tomcat’s Thread Pool
45:35 – Spring WebFlux app – Consumer
49:05 – Netty Event Loop Threads (reactor-http-nio-XX)
53:43 – Enable Netty Logging in WebFlux
57:25 – WebFlux + Netty: End-to-End Flow
01:01:38 – DispatcherHandler (WebFlux entry point)
01:02:58 – RequestMappingHandlerMapping
01:04:13 – HandlerAdapter
01:04:31 – ResponseBodyResultHandler
01:06:06 – Logging the response body
01:11:55 – Non-blocking call with WebClient
01:16:48 – Tuning ioWorkerCount
01:19:44 – Boss thread example
01:21:15 – WebFlux flow diagram
01:24:38 – Q&A
#SpringWebFlux #netty #eventloop #reactiveprogramming #springboot #microservices

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