Crossbar is an application and framework for web-based reporting applications (see http://www.crossbar.info/\).
The 0.5.4 release implements a rudimentary Report Writer. With this release, you can use an HTML form to specify a JDBC datasource, name a report, specify an SQL select statement, and specify where you want the link to appear in the navigation menu. There's a lot of functionality here: If you are building a web app that displays tables of data from a database, you can use Crossbar immediately without writing any Java code. Of course, if you want to write Java code, you can take a look at the Crossbar Model classes and derive any sophisticated reporting mechanism that you need.