SpringMVC 的工作原理和机制

太过爱你忘了你带给我的痛 2022-05-30 00:51 174阅读 0赞

工作原理  
上面的是springMVC的工作原理图：

1、客户端发出一个http请求给web服务器，web服务器对http请求进行解析，如果匹配DispatcherServlet的请求映射路径（在web.xml中指定），web容器将请求转交给DispatcherServlet.

2、DipatcherServlet接收到这个请求之后将根据请求的信息（包括URL、Http方法、请求报文头和请求参数Cookie等）以及HandlerMapping的配置找到处理请求的处理器（Handler）。

3-4、DispatcherServlet根据HandlerMapping找到对应的Handler,将处理权交给Handler（Handler将具体的处理进行封装），再由具体的HandlerAdapter对Handler进行具体的调用。

5、Handler对数据处理完成以后将返回一个ModelAndView()对象给DispatcherServlet。

6、Handler返回的ModelAndView()只是一个逻辑视图并不是一个正式的视图，DispatcherSevlet通过ViewResolver将逻辑视图转化为真正的视图View。

7、Dispatcher通过model解析出ModelAndView()中的参数进行解析最终展现出完整的view并返回给客户端。

工作机制是什么

### Control的调用（续） ###

接着对于（二）的补充：主要是小结下Control的处理逻辑的关键操作；

对于control的处理关键就是：DispatcherServlet的handlerMappings集合中根据请求的URL匹配每一个handlerMapping对象中的某个handler,匹配成功之后将会返回这个handler的处理连接handlerExecutionChain对象。而这个handlerExecutionChain对象中将会包含用户自定义的多个handlerInterceptor对象。

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      <code style="white-space:pre-wrap; background:none; border:0px; float:none; line-height:1.8em; margin:0px; padding:0px; vertical-align:baseline; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace; min-height:auto">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
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      <code style="white-space:pre-wrap; background:none; border:0px; float:none; line-height:1.8em; margin:0px; padding:0px; vertical-align:baseline; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace; min-height:auto; color:rgb(0,0,0)">}</code> 
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     <div style="background:rgb(244,244,244) none; border:0px; float:none; line-height:1.8em; margin:0px; padding:0px 1em; vertical-align:baseline; min-height:auto"> 
      <code style="white-space:pre-wrap; background:none; border:0px; float:none; line-height:1.8em; margin:0px; padding:0px; vertical-align:baseline; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace; min-height:auto">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="white-space:pre-wrap; background:none; border:0px; float:none; line-height:1.8em; margin:0px; padding:0px; vertical-align:baseline; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace; min-height:auto; color:rgb(0,0,0)">HandlerExecutionChain handler = hm.getHandler(request);</code> 
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      <code style="white-space:pre-wrap; background:none; border:0px; float:none; line-height:1.8em; margin:0px; padding:0px; vertical-align:baseline; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace; min-height:auto">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="white-space:pre-wrap; background:none; border:0px; float:none; line-height:1.8em; margin:0px; padding:0px; vertical-align:baseline; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace; min-height:auto; color:rgb(0,0,255)">return</code>&nbsp; 
      <code style="white-space:pre-wrap; background:none; border:0px; float:none; line-height:1.8em; margin:0px; padding:0px; vertical-align:baseline; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace; min-height:auto; color:rgb(0,0,0)">handler;</code> 
     </div> 
     <div style="border:0px; float:none; line-height:1.8em; margin:0px; padding:0px 1em; vertical-align:baseline; min-height:auto"> 
      <code style="white-space:pre-wrap; background:none; border:0px; float:none; line-height:1.8em; margin:0px; padding:0px; vertical-align:baseline; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace; min-height:auto">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="white-space:pre-wrap; background:none; border:0px; float:none; line-height:1.8em; margin:0px; padding:0px; vertical-align:baseline; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace; min-height:auto; color:rgb(0,0,0)">}</code> 
     </div> 
     <div style="background:rgb(244,244,244) none; border:0px; float:none; line-height:1.8em; margin:0px; padding:0px 1em; vertical-align:baseline; min-height:auto"> 
      <code style="white-space:pre-wrap; background:none; border:0px; float:none; line-height:1.8em; margin:0px; padding:0px; vertical-align:baseline; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace; min-height:auto">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="white-space:pre-wrap; background:none; border:0px; float:none; line-height:1.8em; margin:0px; padding:0px; vertical-align:baseline; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace; min-height:auto; color:rgb(0,0,0)">}</code> 
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     <div style="border:0px; float:none; line-height:1.8em; margin:0px; padding:0px 1em; vertical-align:baseline; min-height:auto"> 
      <code style="white-space:pre-wrap; background:none; border:0px; float:none; line-height:1.8em; margin:0px; padding:0px; vertical-align:baseline; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace; min-height:auto">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="white-space:pre-wrap; background:none; border:0px; float:none; line-height:1.8em; margin:0px; padding:0px; vertical-align:baseline; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace; min-height:auto; color:rgb(0,0,255)">return</code>&nbsp; 
      <code style="white-space:pre-wrap; background:none; border:0px; float:none; line-height:1.8em; margin:0px; padding:0px; vertical-align:baseline; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace; min-height:auto; color:rgb(0,0,255)">null</code> 
      <code style="white-space:pre-wrap; background:none; border:0px; float:none; line-height:1.8em; margin:0px; padding:0px; vertical-align:baseline; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace; min-height:auto; color:rgb(0,0,0)">;</code> 
     </div> 
     <div style="background:rgb(244,244,244) none; border:0px; float:none; line-height:1.8em; margin:0px; padding:0px 1em; vertical-align:baseline; min-height:auto"> 
      <code style="white-space:pre-wrap; background:none; border:0px; float:none; line-height:1.8em; margin:0px; padding:0px; vertical-align:baseline; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace; min-height:auto">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="white-space:pre-wrap; background:none; border:0px; float:none; line-height:1.8em; margin:0px; padding:0px; vertical-align:baseline; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace; min-height:auto; color:rgb(0,0,0)">}</code> 
     </div> 
    </div> </td> 
  </tr> 
 </tbody> 
</table>

而对于handlerInterceptor接口中定义的三个方法中，preHandler和postHandler分别在handler的执行前和执行后执行，afterCompletion在view渲染完成、在DispatcherServlet返回之前执行。

PS:这么我们需要注意的是：当preHandler返回false时，当前的请求将在执行完afterCompletion后直接返回,handler也将不会执行。

在类HandlerExecutionChain中的getHandler()方法是返回object对象的；

这里的handler是没有类型的，handler的类型是由handlerAdapter决定的。dispatcherServlet会根据handler对象在其handlerAdapters集合中匹配哪个HandlerAdapter实例支持该对象。接下来去执行handler对象的相应方法了，如果该handler对象的相应方法返回一个ModelAndView对象接下来就是去执行View渲染了。

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## Model设计 ##

如果handler兑现返回了ModelAndView对象，那么说明Handler需要传一个Model实例给view去渲染模版。除了渲染页面需要model实例，在业务逻辑层通常也有Model实例。

ModelAndView对象是连接业务逻辑层与view展示层的桥梁，对spring MVC来说它也是连接Handler与view的桥梁。ModelAndView对象顾名思义会持有一个ModelMap对象和一个View对象或者View的名称。ModelMap对象就是执行模版渲染时候所需要的变量对应的实例，如jsp的通过request.getAttribute(String)获取的JSTL标签名对应的对象。velocity中context.get(String)获取$foo对应的变量实例。

ModelMap其实也是一个Map,Handler中将模版中需要的对象存在这个Map中，然后传递到view对应的ViewResolver中。

不同的ViewResolver会对这个Map中的对象有不同的处理方式；

*  velocity中将这个Map保存到VelocityContext中。
 *  JSP中将每一个ModelMap中的元素分别设置到request.setAttribute(modelName,modelValue);

\-----------------------邪恶的分割线-----------------------------------------------

## view设计 ##

在spring MVC中，view模块需要两个组件来支持：RequestToViewNameTranslator和ViewResolver

对于 ViewResolver，前面有写到了，就不写了；

\-----------------------邪恶的分割线-------------------------------------------------

RequestToViewNameTranslator：主要支持用户自定义对viewName的解析，如将请求的ViewName加上前缀或者后缀，或者替换成特定的字符串等。

ViewResolver：主要是根据用户请求的viewName创建适合的模版引擎来渲染最终的页面，ViewResolver会根据viewName创建一个view对象，调用view对象的Void render方法渲染出页面；

下面来总结下 Spring MVC解析View的逻辑：

*  dispatcherServlet方法调用getDefaultViewName（）方法；