position fixed
add PostTag class
post tag relation
PostTag class ready, but may need other kind of POJO
based on relation scheme
DAOCommand interface
MySQLManager execute
DBManager interface
add a service class to test dao
LoginCheck service
DBManager can execute this kind of cmd
add transaction, but not better exception handler
DAOCommand, service layer can call the class that impls this interface
mv to service package
refresh package
add QueryHelper to POJO
QueryHelper should get a connection from out
move logic to service layer
rm the close connection method
add batch operate
newpost and posttag execute complete, next is post tag relation