Briefly understand MVC and three-tier architecture

MVC

Speaking of mvc We are going to talk about java web Development history of ：

First , At the start of the java Is used in the servlet Terminal , and servlet It is a logic program running on the server , however web Applications definitely need pages , So at this time java web Formed servlet > java + HTML +CSS + javascipt.

But later I found that it would be very inconvenient to write like this , If you modify the code, you need to restart the server frequently .

therefore , There are new technologies JSP.

JSP take HTML+CSS These front-end codes are separated , Therefore, there is no need to restart the server after modifying the page , Just refresh the browser , At the same time, it supports jsp Write in the page java Code , Because it is so convenient , As a result, there is no need to use it later servlet, Direct logic ,jdbc Both ends are written in jsp page .

But it was later found that this was not possible , Because a lot of java、HTML、CSS,JS Code coupled together , It's very troublesome to strip part of the code later .

until MVC The emergence of patterns , It compulsorily divides our code into ：model + view +controller

controller（ Control layer ）

Control the flow of our data , stay web In the application, it can be said that it is the interface end

View（ View layer ）

Provide user view interface , That is, to be responsible for HTML + CSS

Model（ The model layer ）

The models here fall into two categories ： Data model and UI Model

Data model is entity class

UI Model is logic

Three layer architecture

Many people will MVC Think it's a three-tier architecture , It's not .

The three-tier architecture model is a pure java Architecture mode of , There is no such thing as page view .

Three layer architecture ：controller + service + dao

controller（ Control layer ）

Control the flow of data , For example, print data from the console or store data in another place , Therefore, it plays a scheduling role .

service（ Service layer ）

Responsible for the logic of the code .

dao（ Persistence layer ）

Dealing with data , Scale database , file .