It is common knowledge that PHP does well in the open-source Web applications space. PHP has numerous representatives for most application categories, and for some it provides a clear leader, like WordPress. On the other hand, most Java counterparts have apparently failed to reach the same popularity.
Below is an overview of the existing open-source PHP and Java implementations for the following categories of applications: forum, blog, wiki and content management systems (CMS). These are among the most commonly used types of on-line software.
There are lots of PHP forum engines in the open-source software arena, including:
phpBB which has 700+ mods and is the winner of the SourceForge.net 2007 Community Choice Awards for the Best Project for Communications category,
vBulletin with 1000+ mods,
punBB having 300+ projects and 150+ styles.
Notice the large amount of plugins for each of these projects. This denotes a large and healthy user base, devoted to both using and extending the core application.
In the area of blogging, the PHP based WordPress is extremely well spread. Chances are that virtually any blog you read is powered by WordPress. The project has 2000+ plugins and at least 5 dedicated printed books. No other PHP blog engine comes close to the popularity of WordPress.
For Java, there are two relevant open-source blog applications: Apache Roller and Pebble. Roller is more feature-rich, but that comes at a considerable price: large footprint and difficult configuration. It is an enterprise application focused on very large blogging sites (e.g. the Sun blogs), but it seemingly fails to satisfy small-scale needs. I have yet to find a plugin developer community around it.
Pebble on the other hand is focused on the other end of the spectrum, providing a much simpler configuration and lower footprint. But I still couldn't find plugins.
In this category, PHP seems to have an overwhelming advantage. The MediaWiki project powers Wikipedia, the largest wiki by far. The project has lots of available extensions, of which 300+ are stable. There are lots of other PHP wiki engines one can choose from, but I just wanted to point out the most prominent one.
Java does not have too many production-ready wiki projects. In my opinion, JspWiki (with 50+ plugins) and XWiki are the most relevant. I wanted to mention SnipSnap as well, however it's development is officially stopped.
Content Management Systems
Content management systems are a handy way of building dynamic sites instead of starting from scratch. PHP seems to provide everything one needs, including a healthy competition among its foremost projects. These are Joomla (2900+ extensions, 14+ books published) and Drupal (3600+ modules, 9+ books). There are also other CMS projects e.g. Mambo and the ancient PHP-Nuke.
Because in most cases CMSs are deployed on a dedicated server, Java should not be at a disadvantage in this category. There are several open-source Java CMSs to choose from: Apache Jackrabbit, Apache Lenya, Alfresco, Liferay, OpenCms, Nuxeo, Magnolia, Jahia etc. Among these, Alfresco (2 printed books and 20+ stable extensions) and Liferay (portlets based, 1 printed book, 25+ portlet plugins) seem the more popular.
A special note for the Java Content Repository API defined by JSR-170. Both Jackrabbit and Magnolia implement it. This means that third-party tools can access their repositories in a standardized way. It is a very good step towards ensuring that information stored inside a JCR compliant repository can outlive a particular JCR implementation.
For now, the JCR API does not seem enough however. The PHP CMS projects are continuously gaining ground, probably because PHP hosting is cheap and easy to set up, and because the projects themselves are highly usable. Take into account that DZone and implicitly JavaZone (the former JavaLobby) are running on Drupal. And I'm sure that Rick and Matt tried to choose the best option while not easily dismissing the Java CMSs.
In the second part of this article, I will try to explore the reasons for the current state and to figure out a way to change it. Meanwhile feel free to add your input to the above, the list of projects is far from exhaustive.