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Javalin

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description Javalin Overview

Javalin is a lightweight web framework for Java and Kotlin that focuses on simplicity and ease of use. It uses Jetty as its default embedded server and employs a straightforward routing syntax with minimal configuration requirements. The framework supports both synchronous and asynchronous request handling and is designed to work well for creating REST APIs and microservices. Javalin's design philosophy emphasizes minimal boilerplate code and intuitive API design for developers familiar with modern web frameworks.

help Javalin FAQ

Can Javalin applications be written in both Java and Kotlin?

Yes. Javalin exposes a compact API designed for both Java and Kotlin, with routes commonly registered through calls such as get, post, and ws.

Which web server does Javalin use by default?

Javalin runs on an embedded Eclipse Jetty server. Javalin 7 moved to Jetty 12 and uses the jakarta.servlet package namespace rather than the older javax.servlet namespace.

Does Javalin support WebSockets and server-sent events?

Yes. Javalin includes APIs for WebSocket endpoints and server-sent events in addition to ordinary HTTP routes, making it suitable for small real-time services.

When would someone choose Javalin instead of Spring Boot?

Javalin suits applications that need direct routing and relatively little framework structure, such as a small JSON API or Kotlin service. Spring Boot provides a much broader dependency-injection and application ecosystem, while Javalin stays closer to Jetty and explicit handler code.

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