Our latest release of the Web Content & Experience Management Report emphasizes the open source Java world. In particular, we've done major updates to our evaluations of Hippo, Magnolia, and OpenCms.
The three platforms seem quite similar on the surface. They are all headquartered in continental Europe, follow a commercial open source model, and can boast longstanding (and comparatively loyal) customer and developer bases.
From there, though, the three projects diverge substantially, including in such areas a repository architecture, component model, user experience paradigm, admin capabilities, and ultimately even business and support models.
In the end, you shouldn't pick a Web CMS solely based on its underlying language. But the good news is that if Java support is important to your team, you have recourse to a broad range of choices, both open source and commercial.
If you're an RSG subscriber, you can download individual chapter updates or the full report immediately.
If you're not a subscriber, you can get your hands on a sample evaluation.