⚡🧵 WEBFLUX/NETTY VS VIRTUAL THREADS/TOMCAT IN SPRING BOOT (REAL-WORLD CHOICE)
⚡🧵 WEBFLUX/NETTY VS VIRTUAL THREADS/TOMCAT IN SPRING BOOT (REAL-WORLD CHOICE)
🔸 TLDR
▪️ WebFlux + Netty = non-blocking I/O on a small event-loop thread set (great for streaming + massive concurrent I/O).
▪️ Spring MVC + Virtual Threads + Tomcat = blocking code stays simple, but concurrency scales better because threads are cheap (Java 21+).
▪️ For most CRUD apps with JPA/JDBC/legacy SDKs, MVC + virtual threads is often the pragmatic default today.
🔸 THE CORE “VERSUS” (MENTAL MODEL)
▪️ WebFlux/Netty: “Don’t block. Ever.” ➜ you win when everything is reactive end-to-end (client ↔ server ↔ DB).
▪️ Virtual threads/Tomcat: “Blocking is OK.” ➜ you win when your dependencies are blocking (JDBC, SDKs, filesystem) but you still need high concurrency.
🔸 WHAT SPRING BOOT ACTUALLY DOES
▪️ Virtual threads require Java 21+ and are enabled via: spring.threads.virtual.enabled=true (Boot docs also mention Java 24+ recommended for best experience).
▪️ WebFlux can run on Netty/Tomcat/Jetty/Undertow, but Netty is the common default for reactive apps.
▪️ Reactor Netty uses an Event Loop Group sized ~CPU cores (minimum 4) by default.
🔸 CODE SNIPPET: SPRING MVC + TOMCAT + VIRTUAL THREADS
# application.properties
spring.threads.virtual.enabled=true
🔸 CODE SNIPPET: WEBFLUX + NETTY (NON-BLOCKING ALL THE WAY)
@RestController
▪️ WebFlux + accidental blocking (JPA/JDBC, “just one” SDK call, block()) can silently push work to other schedulers and kill the “event-loop advantage”.
▪️ Virtual threads ≠ faster CPU: they shine when you wait on I/O, not when you’re CPU-bound.
▪️ Deployed on external Tomcat (WAR): your container may keep using its own thread pool, so don’t assume Boot’s virtual-thread setting applies the same way.
🔸 QUICK PICK GUIDE
▪️ Choose MVC + Virtual Threads + Tomcat when:
▪️ You use JPA/JDBC, blocking clients, or lots of “normal enterprise” libs
▪️ You want simple debugging + familiar stack
▪️ You need better concurrency without rewriting everything reactive
▪️ Choose WebFlux + Netty when:
▪️ You do streaming (SSE/WebSocket), fan-out calls, high concurrent connections
▪️ You can keep the chain reactive end-to-end (reactive DB, reactive clients)
▪️ You benefit from backpressure and non-blocking resource usage
🔸 TAKEAWAYS
▪️ Virtual threads reduce the main reason people used reactive: “threads are expensive.”
▪️ WebFlux still wins for true reactive pipelines + streaming/backpressure scenarios.
▪️ The best default for many teams in 2026: MVC + virtual threads, and reach for WebFlux when the use case demands it.
#SpringBoot #Spring #Java #VirtualThreads #ProjectLoom #SpringWebFlux #ReactorNetty #Tomcat #Netty #ReactiveProgramming #BackendEngineering #Microservices #PerformanceEngineering
Go further with Java certification:
Java👇
Spring👇
SpringBook👇
JavaBook👇