SpringMVC工作原理

参考文章http://www.roseindia.net/spring/how-spring-mvc-works.shtml

SpringMVC基于MVC设计模式。它所包含的主要的类如下：


● DispatcherServlet
The DispatcherServlet is  configured in the web.xml file and required URL patterns are mapped to this Servlet. It works as the front controller and handle all the request from the user.
我们必须在web.xml文件中配置DispatcherServlet，使用相应的URL地址映射该Servlet。
该类作为前端控制器，负责处理所有用户请求。

● ModelAndView
This class works as the holder for both Model and View in Spring MVC.
该类用于保存模型以及视图。


Simplified Spring MVC architecture diagram
SpringMVC构架缩略图



Let's understand the sequences of the events happens when a request is received by the Spring MVC. Following events happens when DispatcherServlet receives are request:

1.The DispatcherServlet configured in web.xml file receives the request.
在web.xml中配置的DispatcherServlet会接受所有请求。

2.The DispatcherServlet finds the appropriate Controller with the help of HandlerMapping and then invokes associated Controller.
DispatcherServlet通过HandlerMapping类的帮助，找到合适的控制器，并进行调用。

3. Then the Controller executes the logic business logic (if written by the programmer) and then returns ModeAndView object to the DispatcherServlet.
然后控制器执行业务逻辑运算，并返回一个ModelAndView对象给DispatcherServlet.


4.The DispatcherServlet determines the view from the ModelAndView object.
Then the DispatcherServlet passes the model object to the View.
DispatcherServlet通过ModelAndView对象来决定视图。 然后后将模型对象传给视图。

5. The View is rendered and the Dispatcher Servlet sends the output to the Servlet container. Finally Servlet Container sends the result back to the user.
视图被补全，DispatcherServlet将输出结果发送给Servlet容器。
最终Servlet容器将结果返回给用户。

(The View is rendered实在不知道怎么翻译，感觉意思就是创建好了视图部分的意思吧。）



Request flow in Spring MVC
请求流程

SpringMVC是请求驱动(request driven)的，通过DispatcherServlet来处理所有用户发来的请求并给Controller进行处理。
SpringMVC与Spring IOC容器紧密整合在一起，这样用户koi可以使用所有的Spring框架的功能。


下图显示了SpringMVC的请求流程：



过程如下：
1. Client access some URL on the server.

2. The Spring Front Controller(DispatcherServlet) interceptes the Request. After receiving the request it finds the appropriate Handler Mappings.
Spring前端控制器(DispatcherServlet)截取到该请求，并查询对应的处理映射(Handler Mappings)

3. The Handle Mappings maps the client request to appropriate Controller. In this process framework reads the configuration information from the configuration file or from the annotated controller list.
Handle Mappings将用户的请求映射到对应的控制器。（框架通过配置文件信息或者注释信息来完成这一过程)

4. Then the Controller processes the Client Request, it executes the logic defined in the Controller method and finally returns the ModelAndView object
back to the Front Controller.
之后控制器处理用户请求，并执行业务逻辑代码，最终将ModelAndView对象返回给前端控制器。

5. Based on the values in the ModelAndView Controller resolves the actual view, which can be JSP, Velocity, FreeMarker, Jasper or any other configured view resolver.
最终通过ModelAndView控制器中的值形成具体的视图，视图可以是JSP,FreeMarker等等一些配置了的视图解析器。

6. Then the selected view is rendered and output is generated in the form of HttpServletResponse. Finally Controller sends the response to the Servlet container, which sends the output to the user.
视图被做好了， 而输出也被存放入HttpServletResponse。
最终控制器将response返回给Servlet容器，Servlet容器再返回给用户。