I have been programming in Java since Sun released V1.0.  Here are some of the open source projects I have been involved  with.

Apache Torque (db.apache.org/torque)

In designing a Web applications component system for work, I decided to use Torque as the database interface.  It had many nice features that helped get the project up and going quickly.  Unfortunately, the MS SQL server "adaptor" was a bit old and neede refreshing... and then my project needed a few extra features... so one thing led to another and now I am currently a Project Management Committee member for the Apache Software Foundation DB / Torque project.  

Torque Add-ins (torque-addons.sourceforge.net)

I created this SourceForge project to offer some add in functionality to the Torque package. The intent was for other developers to add to this.  Currently it included two Add-In packages that I wrote, the Torque Betwixt Templates and the XML Import / Export Add-in.  

These add-in were designed to allow data to be easily transported between sites via XML without having to write much code.  The Torque generator would create the required support for this.  It was used internally at my work as part of a REST API used to sync info across a firewall.

jForum (jforum.net)

jForum is a java base phpBB clone that became much more.  It is quite scaleable.  In fact, EA Games uses it as the basis for it's online forums.  

I got involved in jForum when we selected it to be the "forum" component in our web applications.  It was Java based and had a robust "Single Sign on" api.  To learn it, I ended up hanging out on the (now defunct) support forum.  In the spirit of giving back to the community, I became one of the major "experts" answering questions posted.

Unfortunately, the developer decided to drop the support forum after his server crashed.