introduction:
You will find that when using the Eclipse development tool to write Java Web project, a medium-sized or large-scale projects with the increase in code, you will find: The code can be written in the src directory, you can also write in the WebContent directory. Src can be built under a lot of packages, a lot can be built under the WebContent folder.
So the question arises: in the end to write a new class which file in which directory to the folder?
At this solution is: the need to regulate a pattern, which in the end the class where to write.
MVC design pattern:
View View
Responsible for page display; interaction with the user. It contains a variety of forms. Techniques are used to achieve view html / css / jsp / js other front-end technology.
User interaction: the user click on a page; page in a variety of forms to fill in and so on ........
Model Model
Model responsible for implementing each function (such as login, add, delete function). JavaBean model implemented.
| JavaBeans : ① Java is in a special class (in other words: JavaBean is a Java class). A Java class that meets the following requirements, can be called a JavaBean a. public class modified, that provides a public constructor with no arguments b. All properties are private c. Provide getter and setter methods
② from the use of perspective, JavaBean divided into two categories: a business logic package the JavaBean. (EG: LoginDao.java encapsulates the login logic) b JavaBean encapsulated data. (entity classes: eg:. Student.java Vedio.java often corresponds to a table in the database, i.e. the database table has a Student, there projects a Student.java class)
③JavaBean is a reusable component to achieve some common functions by writing a component, "write once, execute anywhere, anywhere reuse." |
Controller Controller
控制器负责将视图与模型一一对应起来。相当于一个模型分发器。所谓分发就是：①接收请求，并将该请求跳转（转发，重定向）到模型进行处理。②模型处理完毕后，再通过控制器，返回给视图中的请求处。建议使用Servlet实现控制器。
三层架构：
首先来说，三层架构与MVC的目标一致：都是为了解耦和、提高代码复用。MVC是一种设计模式，而三层架构是一种软件架构。
三层架构分为：表现层（UI）、业务逻辑层（BLL）、数据访问层（DAL）再加上实体类库（Model）
1.实体类库（Model），在Java中，往往将其称为Entity实体类。数据库中用于存放数据，而我们通常选择会用一个专门的类来抽象出数据表的结构，类的属性就一对一的对应这表的属性。
·一般来说，Model实体类库层需要被DAL层，BIL层和UI层引用。
2.数据访问层（DAL），主要是存放对数据类的访问，即对数据库的添加、删除、修改、更新等基本操作
·DAL就是根据业务需求，构造SQL语句，构造参数，调用帮助类，获取结果，DAL层被BIL层调用
3.业务逻辑层（BLL）
·BLL层好比是桥梁，将UI表示层与DAL数据访问层之间联系起来。所要负责的，就是处理涉及业务逻辑相关的问题，比如在调用访问数据库之前，先处理数据、判断数据。
BLL层只被UIL层引用
- 用户表现层（UIL）,就是用户看到的主界面。
各层引用关系如下图所示：
MVC与三层架构的对应关系，图示如下：
