Relationship among controller, service and Dao

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Preface

Tips ： Here you can add the general content to be recorded in this article ：

I mentioned the code writing process in the last article
1、 Draw page , To write A.jsp
2、 Write the customer request address , Initiate customer request , To write B.jsp
3、 Write control layer code (xxxController.java)
4、 Write business layer code （xxxService.java)
5、 Write data persistence layer code （xxxDao.java and xxxDao.xml)
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Today, let's talk about their relationship

Tips ： The following is the main body of this article , The following cases can be used for reference

One 、model

model Layer is the database entity layer , Also known as entity layer ,pojo layer
Generally, a table in a database corresponds to an entity class , Class attributes are the same as table fields One A corresponding .

Generally, the entity layer will automatically generate Getter、Setter、to String Methods and construction methods

Eclipse Quickly add Getter、Setter Method

Eclipse Quickly add to String Method

Eclipse Quickly add construction methods in

idea Quickly add Getter、Setter Method

Here we borrow the classic dynamic pictures on the Internet ：

idea Quickly add to String Method

idea Quickly add construction methods in

Here we borrow the classic dynamic pictures on the Internet ：

Two 、Controller Business control layer

controller The function of the layer is request and response control .
controller The layer does not allow direct operation of the database ！controller The layer is responsible for the interaction between the front end and the back end , He is a bridge , Set up the communication between the outside world and the business layer , Accept front-end requests , call Serice Layer to control the business process , receive service The data returned by the layer , Finally, return the specific page and data to the client .
It's like a company's front-line staff wants to see the feedback from the company's boss , So the front-line staff will communicate their purpose through the manager and the boss , The manager then asked the boss for instructions , Finally, the feedback from the boss is transferred to the front-line staff .

in addition ,Service It will play a great role in future distributed deployment , It's like a waiter , Which table of guests need to order , Just call the waiter ！ Corresponding , What kind of business does the outside world need to complete , Just through Controller To call different Service, Here's the thing to remember ,Controller Just a middleman or forwarder , Should not be in Controller Exposed in Service Business logic of , Instead, it should be forwarded directly Service Business processing results ！

3、 ... and 、Dao Database persistence layer ;

dao Layers are also called mapper layer .
dao Layer is to deal with the database , Some of the tasks responsible for contacting the database are encapsulated here ,dao The layer sends data to the database SQL sentence , Complete the task of data addition, deletion, modification and query .

dao The design of the layer is first of all design dao The interface of , And then in Spring The implementation class of this interface is defined in the configuration file of , Then you can call this interface in the module for data service processing. , You don't need to worry about which implementation class of this interface is , Very clear structure ,DAO Data source configuration for layer , And the database connection parameters are Spring Configuration in the configuration file .

DAO The master plan of design needs and the table of design , And implementation classes One A corresponding .
DAO The methods in the interface defined by layer are similar , It's up to us to DAO Layer to the database access operation to determine , Operation on Database , What we basically need to use is to add , Delete , to update , Query methods .
thus DAO The layer should basically cover the operations corresponding to these methods . besides , You can define some custom special database access methods .

Four 、Service The business layer / Service layer ;

service Layers are built on dao Above the layers , Established dao You can set up after layer Service layer , and service Layer is again controller Below that layer ,service Layer calling dao Layer interface , But also provide an interface to controller Layer to call , It's just in the middle of a layer .

All internal business logic will be handled here ,
For example, user's addition, deletion, modification and query , Or send a verification code or email , Or do a lottery and so on , Will be in service In the middle of ,service Layer calls dao Layer interface , receive dao The data returned by the layer , Complete the basic function design of the project , therefore Dao Layers are essential ;

Every model has one service Interface , Each interface encapsulates its own business processing method .

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summary

DBUtil.java
General , One Controller Corresponding to one Service, One Service Corresponding to one Dao, One Dao Corresponding to a database table ,
Of course, depending on the complexity of the project or business , One Controller You can call multiple Service, And one Service You can also call multiple Dao, however Controller Layer does not allow intermodulation ,Service Layers also do not allow intermodulation ,
Namely AController Can't call directly BController
AService You can't call directly BService, Follow the principle of high cohesion and low coupling

Part of the content of this article draws on the articles of other bloggers , But I forgot which article , I would like to thank the blogger of the original article