MVC mode three-tier architecture

MVC Pattern

        MVC yes Model-View-Controller（ Model - View - controller ） For short , Its main function is to View presentation is separated from business control code

Model（ Model ）:

         Refers to data perhaps Source of data
         It's a data model , It refers to the data obtained , And it is encapsulated . It is usually an entity class object . But the data source of entity class objects , Through the three-tier architecture Business layer and persistence layer （ We call it business model ）

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View （ View ）:

         Refers to Visual interface
         It is used to display data . It's what we learned before jsp and html. It can be either jsp, It can also be html. In our later study , It can also be a mobile display

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Controller（ controller ）:

         controller Act on models and views , Responsible for the scheduling of requests , it Separate the view from the model
         He is used to handle requests , He separates the data model from the view , Dispatch from . Let logic control , The presentation data and the encapsulated data model are independent of each other .
         He is what we learned before Servlet, We will learn later Filter Of , It can also be used as a controller . But now it is Servlet. 

Three layer architecture

         In order to achieve a clear level of code , A clear division of responsibilities , Usually, an application is divided into three layers ： The presentation layer 、 Business logic layer 、 Data access layer .

 The presentation layer (web layer )： Data interaction with browser  
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 The business layer (service layer ):  Dedicated to processing business logic  
                com.itheima.service

 Persistence layer (mapper layer ):  Data exchange with database 
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