Servlet containers

Servlet containers

Servlet Container	Blocking HTTP Requests	Non-Blocking HTTP Requests	WebSockets Support	Works Well with Kotlin Coroutines
Jetty	✅ Yes	✅ Yes (via async I/O)	✅ Yes	✅ Yes (with Coroutine-based APIs)
Tomcat	✅ Yes	✅ Yes (via async servlets)	✅ Yes	⚠️ Limited (needs adapters like ktor-server-tomcat)
Netty (is not a servlet container—it's an event-driven network application framework that can be used to build non-blocking servers and clients)	⚠️ Not its primary model	✅ Yes (fully event-driven)	✅ Yes	✅ Yes (integrates well with Ktor and coroutines)
Undertow	✅ Yes	✅ Yes (reactive streams)	✅ Yes	✅ Yes (used in ktor-server-undertow)

Clients

HTTP Client	Blocking Requests	Non-Blocking Requests	Coroutine Friendly	Additional Notes
RestTemplate	✅ Yes	❌ No	⚠️ Limited	Synchronous API, designed for Spring MVC.
WebClient	⚠️ Limited	✅ Yes	✅ Yes	Non-blocking, reactive web client from Spring WebFlux.
Ktor	✅ Yes	✅ Yes	✅ Yes	Designed for Kotlin; supports both blocking and non-blocking calls.
OkHttp	✅ Yes	✅ Yes	⚠️ Limited	Primarily synchronous but supports asynchronous requests; good for Kotlin coroutines.
Apache HttpClient	✅ Yes	⚠️ Limited	⚠️ Limited	Synchronous by default; can use Future for async.
Retrofit	✅ Yes	✅ Yes	✅ Yes	Works with OkHttp, designed for REST APIs; supports coroutines via extensions.
Vert.x Web Client	❌ No	✅ Yes	✅ Yes	Fully non-blocking and designed for asynchronous programming.