Model: the model of things, such as Person.java, the definition of human behavior attributes. pojo, OR maping, persistence
Dao: operation code is written at a persistence, docking with the database, such as Person, CRUD.
Service: is the code that implements the business layer. Call the dao layer interface.
Controller: is the user page access control layer, such as a jump, call to the method specific business logic layer Service interface.
View: user view layer, i.e., the page code html, js like.
