Xiaobo Yang and Robert Allan wrote an interesting article tutorial for integrating portlets and AJAX in your applications. Many web portals are based on Java portlet technology. Progress bars for file upload have been described using Ajax, but so far there are none that are portlet based. This article shows how to develop an Ajax-based file upload portlet that displays a progress bar. The portlet is useful for those who need to share large audio, video, and scientific files.
To follow this article, you should be familiar with Web development using Java Servlets and JavaServer Pages (JSPs). Also, it is essential that you understand portal and portlet technology development. However, if you are not proficient with portlet technology, don't abandon the article now because you'll find a brief introduction to portlet technology as well as useful resources you can use to help you get up to speed. The cornerstone of your file upload portlet is the Apache Commons FileUpload package (also referred to as FileUpload in this article). In addition to file upload support in a servlet, the Apache Commons FileUpload Version 1.1 package supports file upload in a portlet as well. This article uses Apache Commons FileUpload Version 1.2.
The authors used Direct Web Remoting for AJAX support in the portlet because of its ease in allowing Javascript to interact with server-side Java objects.