From the Struts user mailing list:
Since its release in June 2001, Apache Struts has become the most popular web framework for
Java. Six years later, by any objective measure, Struts is still Java's most popular web framework.
In February and March 2007, the group released both Struts 1.3.8 and Struts 2.0.6 to the general public, and Struts downloads zoomed to over 340,000 a month from the Apache site alone. And this is just the tip of the iceberg. Most copies of Struts are downloaded from an network of mirrors or obtained from Maven repositories.
So how popular is Struts compared to the other heavy hitters like Spring and Hibernate? Spring has about 1/2 as many (80K) downloads in the same period and so does Hibernate. How do MyFaces, Wicket and Tapestry stack up? Here's their best download numbers in the past few months:
Sorry JSF, you appear to be losing. Badly. This is an incorrect statement as pointed out by commentors. Thanks for keeping me honest guys.
Disclaimer: Yes, I realize that these statistics are not very accurate, especially considering Maven. Unfortunately, until Maven has repository download stats, this information is the best we've got.