One of Struts' most important selling points has been the large number of third-party extensions available for the framework. If there is a feature that Struts doesn't offer itself, it's likely that someone has developed an extension that supplies that feature and made it available for the community to use. Simply put, the third-party extensions have contributed greatly to the growth and popularity of Struts over the past several years because they have significantly expanded the richness of the Struts development environment.
As developers have adopted Struts and added functionality for their specific needs, they have contributed a significant amount of that code back to the Struts project itself (e.g., Tiles, Validator, Declarative Exception Handling, Nested Tag Library, etc.). Several third-party extension projects have been created as well. This appendix provides a brief introduction to some of the more popular third-party extensions available for Struts. In addition to the extensions highlighted in this appendix, there is a Struts project hosted at SourceForge (http://struts.sourceforge.net/) that serves as a general repository for Struts extensions.
For a comprehensive list of all of the extensions available for Struts, you can visit the Struts Central Web site at http://www.StrutsCentral.net/. Additionally, the Planet Struts website at http://www.PlanetStruts.org/ provides an archive of all of the latest news about Struts and extensions to the framework.