http://www.javaworld.com/javaworld/jw-09-2003/jw-0905-portlet2_p.html

In this second and final article in Stefan Hepper and Stephan Hesmer's portlet series, the authors move beyond the Portlet API basics outlined in Part 1 to detail the API's reference implementation (RI), known as Pluto. They also offer a series of example portlets to illustrate how you can extend the API's standard functions. (1,700 words; September 5, 2003)