Open Source CMS Solutions Based on Java?

namityadav asks: "I've been looking for an open source Content Management System (CMS) which is widely used / supported, and has features like web-logging, online communities, RSS feeds, forums, polls, calendars, website searching, and so on. The most obvious choices are Drupal (I've played with it in the past) and Joomla, however both of them are PHP based. Since I am a Java developer, I wanted to find something based on Java. To my surprise, I could find some very weak Java based alternatives to Drupal, like MMBase, OpenCMS and Magnolia. Why is it that there are so many PHP based open source CMS which are hugely successful (Drupal is used by The Onion, Spread Firefox, and more), but there is not even one comparable solution based on Java?"