Java web application framework

Wicket (component-based approach)
http://wicket.sourceforge.net/

RIFE (mix of Request-based/Component-based)
http://rifers.org/about

Stripes
http://stripes.mc4j.org/confluence/display/stripes/Home

Tapestry
WebWork
Echo2
Click
Maverick
Millstone
JBlooming
SOFIA
Shale
Chrysalis
StrutsTi