springmvcHandlerMapping解析_晏无心_新浪博客

蔚落 2022-12-20 12:56 191阅读 0赞

Spingmvc中的HandlerMapping负责解析请求URL，对应到Handler进行处理（这里的Handler一般为Controller里的一个方法method，也可以为servlet或者Controller等）

先来看一个http请求的入口DispatcherServlet：

[![springmvcHandlerMapping解析][springmvcHandlerMapping]][springmvcHandlerMapping_springmvcHandlerMapping]  
  
[![springmvcHandlerMapping解析][springmvcHandlerMapping 1]][springmvcHandlerMapping_springmvcHandlerMapping 1]  
  
[![springmvcHandlerMapping解析][springmvcHandlerMapping 2]][springmvcHandlerMapping_springmvcHandlerMapping 2]  
DispatcherServlet继承FrameworkServlet，FrameworkServlet继承HttpServletBean，HttpServletBean继承HttpServlet。

可以看出，springmvc的DispatcherServlet是在Servelt的基础上做了扩展处理。

[![springmvcHandlerMapping解析][springmvcHandlerMapping 3]][springmvcHandlerMapping_springmvcHandlerMapping 3]  
  
[![springmvcHandlerMapping解析][springmvcHandlerMapping 4]][springmvcHandlerMapping_springmvcHandlerMapping 4]  
doService方法为servlet处理请求的入口，DispatcherServlet中做了方法覆盖，doService方法中的doDispatch(request, response)方法，是springmvc处理整个请求流程的关键。

[![springmvcHandlerMapping解析][springmvcHandlerMapping 5]][springmvcHandlerMapping_springmvcHandlerMapping 5]  
mappedHandler = getHandler(processedRequest);

这行代码实现了为请求寻找处理handler，返回的是HandlerExecutionChain；

HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

找到处理handler后，再去找匹配的HandlerAdapter，HandlerAdapter将完成后续处理。

继续看是如何找到请求对应的处理handler的：

[![springmvcHandlerMapping解析][springmvcHandlerMapping 6]][springmvcHandlerMapping_springmvcHandlerMapping 6]  
可以看出是从类变量this.handlerMappings中循环获取，当找到与之匹配的HandlerMapping时，返回类型为HandlerExecutionChain的handler。

这里this.handlerMappings中的值是从哪获取的呢？DispatcherServlet初始化的时候会给this.handlerMappings赋值：

[![springmvcHandlerMapping解析][springmvcHandlerMapping 7]][springmvcHandlerMapping_springmvcHandlerMapping 7]  
  
[![springmvcHandlerMapping解析][springmvcHandlerMapping 8]][springmvcHandlerMapping_springmvcHandlerMapping 8]  
从这里可以看出，在servlet初始化的时候，会对springmvc的HandlerMappings、HandlerAdapters等做初始化。

[![springmvcHandlerMapping解析][springmvcHandlerMapping 9]][springmvcHandlerMapping_springmvcHandlerMapping 9]  
这里三个步骤，先对springmvc.xml里配置的HandlerMapping进行初始化、实例化，再对this.handlerMappings赋值，最后对this.handlerMappings进行排序。

这里的排序就是对HandlerMapping的order属性进行排序，这样，order属性值小的，就可以先对请求进行匹配。

从tomcat启动日志里可以看到HandlerMapping的初始化：

[![springmvcHandlerMapping解析][springmvcHandlerMapping 10]][springmvcHandlerMapping_springmvcHandlerMapping 10]  
这里涉及到两个HandlerMapping：

第一个是BeanNameUrlHandlerMapping，初始化时会将url path做映射存储；

第二个是RequestMappingHandlerMapping，初始化时会将Controller中配置@RequestMapping注解的方法做映射存储。

[![springmvcHandlerMapping解析][springmvcHandlerMapping 11]][springmvcHandlerMapping_springmvcHandlerMapping 11]  
  
[![springmvcHandlerMapping解析][springmvcHandlerMapping 12]][springmvcHandlerMapping_springmvcHandlerMapping 12]  
可以看出，HandlerMapping初始化时，会将映射与handler存储到map里；处理请求时，从map里取出对应的处理handler。

这就是HandlerMapping在springmvc里的大致处理流程，还有很多代码细节需要进一步研究。

接下来将会对HandlerAdapter进行分析

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[springmvcHandlerMapping_springmvcHandlerMapping 11]: /images/20221120/4479b482696f4a588c76ca2bb86c43b6.png
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[springmvcHandlerMapping_springmvcHandlerMapping 12]: http://album.sina.com.cn/pic/004dzziXzy7l1d1yH8Ee4