Useful links:

http://www.manageability.org/blog/stuff/open_source_portal_servers_in_java/view
http://www.ociweb.com/javasig/knowledgebase/2004-09/

Portal Candidates

We want something which is JSR-168 compliant, and preferably is just a web portal, not a content management system with a portal build-in.

• Liferay - Liferay is designed to deploy portlets that adhere to the Portlet API (JSR 168). Many useful portlets are bundled with the portal (Mail, Document Library, Calendar, Message Boards, to name a few) and can be used as examples for adding your own custom portlets.
• UPortal
• Pluto

Portlet Development

• http://java.sun.com/developer/technicalArticles/J2EE/sdk_nbportletplugin/