clock:  	allow users to set preferred timezone
bookjps:	use jpa to persist data
booklowlevel:	use lowlevel api to persist data
types:		put entities of different types
entities:	basic operations on entities
queries:	perform queries
javabook:	interactively put, get, delete and query, it uses JSP in the view layer
guestbookmemcache:	javabook with memcache
transaction:	testing transaction and commit