AJAX is an approach to writing web pages that improves a web sites appeal and usability. It enhances user interaction by targeting updates from the server to specific areas of the web page, known as n-page replacement. It allows information to be changed without long delays or frustrating page refreshes.
DWR (Direct Web Remoting) is easy AJAX for Java. It reduces development time and the likelihood of errors by providing commonly used functions and removing almost all of the repetitive code normally associated with highly interactive web sites