Top Five Java Technologies to Learn in 2008

From: http://www.theserverside.com/news/thread.tss?thread_id=48270

Carlos Perez has posted his list of the top five Java-based technologies to learn in 2008. They are:
• OSGi (a specification for dynamic modules for Java)
• The Java Content Repository spec, first appearing in the JCP in February 2002
• Google Web Toolkit (first released in May, 2006)
• Groovy (first released in May, 2004)
• Cloud computing (a concept designed around the use of virtual servers, or distributed computing without the use of EJB)
It's interesting that these are older technologies that are, perhaps, "coming of age" and have now matured to the point where they're recommended. Certainly, all of these technologies are useful:
OSGi is the module system behind Eclipse,
Groovy is gaining acceptance with its formal specification and continually improved releases,
GWT is also fairly mature and stable, and
Cloud computing is becoming more accepted in the wider marketplace.

JCR and cloud computing are probably the least-accepted of these technologies, and vendors in both spaces are trying to address that, with competitions to spur awareness or active community involvement (see GridGain, Gigaspaces, or Terracotta), or plans for them (watch TSS for an announcement around JCR at TSSJS 2008.)

It's an interesting list. What would you put on your own list of the top five Java technologies to learn for 2008? What technologies are emerging right now that you think will appear on a future version of this list?