@edd has an article out at O'Reilly Radar entitled - Seven Java projects that changed the world Hist list - jUnit, Eclipse, Spring, Solr, Hudson/Jenkins, Hadoop, and Android is a worthy list. Of course, as with any list, one immediately jumps to champion items that have been left off the list and I'm certainly going to seize that opportunity. But first some general impressions about the list.
It struck me that no Java Web Frameworks made the list. No portals/portlets. No OpenSocial widgets. No Struts/JSF/GWT/Flex/etc. I don't disagree with this at all as I don't think any of the options has differentiated itself from the pack. Just an interesting observation.
Second, no SOA/Web Service/XML frameworks like JAX-B, JAX-RS, JAX-WS, etc. No Enterprise Integration frameworks like Apache Camel. Perhaps 5 years ago, this would not have been the case as we SOA was at the top of the Buzz cycle. But the impact for system interoperability and the influence that Java had in driving the equivalent Web Service and XML standards was significant.
The Jilted Frameworks
Entity Beans 2.x anyone? Thank goodness that Hibernate came along and saved us from DAO and JDBC plumbing code madness. Java Persistence Architecture exists because of Hibernate and has done, in my opinion, as much for multi-tier database applications as Spring has for Java EE development. I personally think Hibernate should supplant SOLR and Lucene from the list.
Yes, everyone's favorite build tool to hate. Certainly we had software build frameworks like Ant and Make before Maven came along. And the whole "Convention over Configuration" approach certainly feels restrictive. But the real game changer that Maven brought us was dependency management. Thanks to Maven, we don't have to check-in our Jars into our SCM tool of choice. The introduction of frameworks like Buildr and Apache Ivy certainly help strengthen the case.
So here are my off-the-cuff candidates. It is by no means complete and certain to evolve as Java continues to chart its way in a post-Sun, Oracle-enslaved world.