MVC mode and three-tier architecture

MVC Pattern

Layered development mode , among ：

• M：Model, business model , Deal with business
• V：View, View , Interface display
• C：Controller, controller , Processing requests , Call models and views
  
  controller （serlvlet） Used to receive requests sent by the browser , Controller call model （JavaBean） To get data , For example, query data from the database ; After the controller obtains the data, it is handed over to the view （JSP） Show the data .

Three layer architecture

Divide the project into three levels ： The presentation layer 、 Business logic layer 、 Data access layer

• Data access layer ： On the database CRUD Basic operation
• Business logic layer ： Encapsulate business logic , Basic functions in composite data access layer , Form complex business logic functions . for example Register business functions , We'll call it first Data access layer Of selectByName() Method to determine whether the user name exists , If it doesn't exist, call again Data access layer Of insert() Method to add data
• The presentation layer ： Receiving request , Encapsulated data , Call the business logic layer , The response data

And the whole process is , Browser send request , Expressional Servlet Receive the request and call the method of business logic layer for business logic processing , The business logic layer method calls the data access layer method to operate the data , Return to serlvet, then servlet Leave the data to JSP To display

• The presentation layer ： com.xxxx.controller perhaps com.xxxx.web
• Business logic layer ：com.xxxx.service
• Data access layer ：com.xxxx.dao perhaps com.xxxx.mapper