* The GWT SDK provides a set of core Java APIs and Widgets. These allow you to write AJAX applications in Java and then compile the source to highly optimized JavaScript that runs across all browsers, including mobile browsers for Android and the iPhone. * Constructing AJAX applications in this manner is more productive thanks to a higher level of abstraction on top of common concepts like DOM manipulation and XHR communication. * You can debug AJAX applications in your favorite IDE just like you would a desktop application, and in your favorite browser just like you would if you were coding JavaScript. The GWT developer plugin spans the gap between Java bytecode in the debugger and the browser’s JavaScript. * GWT contains two powerful tools for creating optimized web applications. The GWT compiler performs comprehensive optimizations across your codebase — in-lining methods, removing dead code, optimizing strings, and more. By setting split-points in the code, it can also segment your download into multiple JavaScript fragments, splitting up large applications for faster startup time. * When you’re ready to deploy, GWT compiles your Java source code into optimized, stand-alone JavaScript files that automatically run on all major browsers, as well as mobile browsers for Android and the iPhone.

* Sparks intention is to provide a pure Java alternative for developers that want to (or are required to), develop their web application in Java. Spark is built around Java 8's lambda philosophy, which makes a typical Spark application a lot less verbose than most application written in other Java web frameworks. * Spark focuses on being as simple and straight-forward as possible, without the need for cumbersome (XML) configuration, to enable very fast web application development in pure Java with minimal effort. It’s a totally different paradigm when compared to the overuse of annotations for accomplishing pretty trivial stuff seen in other web frameworks. * Spark is a simple, lightweight and not opinionated pure Java web framework that doesn't get in your way, unlike in other Java web frameworks, you can structure your application as you want.