Javalin is a lightweight web framework for Java and Kotlin, built on top of the Jetty HTTP server. It provides a fluent, consumer-based configuration API for defining HTTP routes, WebSocket endpoints, Server-Sent Events (SSE), static file serving, and more. The framework emphasizes simplicity and developer experience by avoiding annotations and reflection, instead using lambda handlers and a plugin system for extensibility. Core features include request/response handling with before/after lifecycle hooks, path parameter parsing, validation, JSON serialization (Jackson 2/3, Gson), compression (gzip, brotli, zstd), CORS, rate limiting, and SSL/TLS support. The architecture is modular, with separate packages for routing, configuration, plugins, and utilities, and optional satellite modules for metrics (Micrometer), template rendering (multiple engines), and testing tools. Javalin is designed as a library to be embedded in applications, not as a standalone server, and is distributed via Maven Central.
Utopia HTTP is a PHP MVC-based framework for building web applications. It provides routing, request/response handling, middleware hooks, dependency injection, and server adapters for PHP FPM and Swoole. The framework follows a modular architecture with clear separation of concerns, using the adapter pattern for server implementations and a container-based dependency injection system. Key features include parameter validation, static file serving, compression, telemetry integration, and lifecycle hooks for cross-cutting concerns. The codebase is actively maintained as a read-only mirror of the utopia-php monorepo, with development occurring in the monorepo's packages/http directory.