The popularity of some of the technologies/farmeworks can vary demographically. The best way to identify what the prospective employers are looking for or what the industry is passionate about is through some research, which is a vital skill to have.
1. Check your online job advertisements to see what the prospective employers are looking for.
2. Go to
http://www.google.com/trends (Google Trends) and type in the search terms like EJB3, Ajax, Spring,
Struts 2, etc to look at the trend.
3. Regularly visit some of the
Java sites to keep yourself aware of emerging technologies/frameworks and trnda by visiting
--
http://java.dzone.com/
--
http://www.theserverside.com/
--
http://www.infoq.com/
--
http://www.javaworld.com/
--
http://java.sys-con.com/, etc
where you can learn from industry experts.
In general, you can't go wrong with learning Web Services, EJB3, Spring, Ajax, JMS, and Hiberante. Spring is vast and pick the ones like IoC (aka DI), Spring AOP, popular templates for
JDBC, JMS, Hibernate, etc.