DWR, or Direct Web Remoting is a Java open source library which helps developers wanting to write web sites that include Ajax technology. It allows code in a web browser to use Java functions running on a web server as if those functions were within the browser. It consists of 2 main parts:
Echo2 is the next-generation of the Echo Web Framework, a platform for developing web-based applications that approach the capabilities of rich clients. The 2.0 version holds true to the core concepts of Echo while providing dramatic performance, capability, and user-experience enhancements made possible by its new Ajax-based rendering engine.
OpenFaces is a JSF library that provides an extended set of AJAX-powered JSF components, an Ajax framework and validation framework that shifts the traditional JSF validation to the client side. The component suite of OpenFaces includes both visual and auxiliary non-visual components that give you more control over your Web application usability.
WebGalileo Faces is a set of highly customizable reusable Open Source user interface Java Web Components for Rich Internet Applications. With full support for the Sun Java Server Faces specification, AJAX, WebGalileo Faces provides developers with the tools needed to easily capture and respond to UI events in the browser. Using the components developers can concentrate their efforts on the business logic of an application and not the details of client side user interface elements.