My Kotlin/Java REST Library Javalin Reaches v0.4.0 (CORS, Uploads, ++)

In plain words

Javalin is a REST API library for Kotlin and Java that simplifies web development. Version 0.4.0 introduces built-in CORS support through the enableCorsForOrigin() method, file upload handling, and improved parameter mapping with destructuring capabilities in Kotlin. The update also refactors Jackson configuration to use JavalinJacksonPlugin.configure(). It is designed for developers building REST services with Kotlin or Java.

written from the facts on this page · September 2026

From the sources

Javalin 0.4.0 adds built-in CORS support with app.enableCorsForOrigin("origin") . There were also some breaking changes made to Jackson and the template-engines. If you want to configure Jackson now, you’ll have to call JavalinJacksonPlugin.configure() instead of just Jackson.configure() . There were also other minor adjustments and bugfixes, see the news overview for a completefrom javalin.io

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