Screaming Penguin

Thus far OpenSymphony is flat out fantastic. OpenSymphony is a host of well organized, fairly well documented reusable J2EE components (great for web applications).

I stumbled onto "OsCache" on another project, OsCache is the cache component of OpenSymphony. It allows dynamic J2EE webapps to cache pages for greatly improved performance AND CATCH THIS it will serve the cached page if an error occurs and NOT THE error page. Now thats just damn cool.

They components for data access and persistence, style and presentation and total web components through "WebWork".

WebWork is a web application framework for J2EE. It is based on a concept called "Pull HMVC" (Pull Hierarchical Model View Controller). It supports an arrange of view technologies - XSLT, JSP, Velocity, Applet, Jasper Reports, and more. [requires Servlet 2.3 / JSP 1.1]

For more check em out: OpenSymphony.