SpringMVC源码流程分析

旧城等待， 2021-11-22 09:40 441阅读 0赞

**DispatcherServlet源码分析**

> SpringMVC核心的就是DispatcherServlet，所有的请求都会转发到DispatcherServlet，让后在通过DispatcherServlet执行具体的控制层（Handler） 返回modelAndView给客户端视图展示。

**DispatcherServlet与Servlet关系**

> 关系：DispatcherServlet继承FrameworkServlet继承HttpServlet
> 
> 流程执行关系：
> 
> HttpServlet service方法 判断请求方法的类型
> 
> FrameworkServlet doService
> 
> DispatcherServlet doService

**DispatcherServlet源码流程分析**

*  1.执行doDispatch
 *  2.调用getHandler方法获取请求目标的方法  也就是  请求url映射路径对应的控制层具体的方法
 *  handlerMappings的作用查找控制器位置，比如xml和注解方式。
 *  3.调用getHandlerAdapter获取控制层适配器 RequestMappingHandlerAdapter
 *  4.执行拦截器前置方法 preHandle() 如果返回为true的话
 *  5.执行实际请求目标方法 返回modeAndView对象
 *  6.执行拦截器PostHandle()方法
 *  7.设置渲染视图层内容
 *  8.执行拦截器afterCompletion方法

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70][]

现在先从最开始的web.xml文件进行分析，我们首先配置了contextConfigLocation如下所示：  
![20190725103522813.png][]

![2019072510401179.png][]

继承关系如下图所示:

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 1][]

> 上图中的ServletContextListener该类位于servlet-api.jar包中（再tomcat的自带lib中可以找到）   
> ContextLoaderListener实现了ServletContextListener接口，该接口保证了在能够为客户端提供服务之前向ServletContext中添加任何对象。每个Web应用都有一个ServletContext与之相关联，启动时被创建，关闭时被销毁，并且ServletContext在全局范围内有效。ServletContextListener的核心逻辑就是初始化WebApplicationContext实例并放入ServletContext中。   
> 我们之所以使用了ContextLoaderListener是为了避免下面这种硬编码配置:  
> ApplicationContext ac = new ClassPathXmlApplecation("applicationContext.xml")

再来说说ContextLoaderListener的实际步骤是：

1.  webApplication存在性验证（配置中只能有一个ServletContextListener接口，验证的方法就是检查该属性是否存在） 
2.  创建webApplication实例 
3.  将属性注入（例如contextConfigLocation）webApplication 
4.  将实例记录到servletContext中 
5.  映射当前的类加载器与创建的实例到全局变量currentContextPerThread中

讲完了ContextLoaderListener再来讲讲web.xml中另一个重要配置DispatcherServlet，对于DispatcherServlet的配置如下所示：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 2][]

接下来我们先给出DispatcherServlet的类层次结构，如下图所示：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 3][]

### 注册url与HandlerMethod映射关系链 ###

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 4][]

Spring容器启动时, 在org.springframework.web.servlet.handler.AbstractHandlerMethodMapping类

![20190725150307129.png][]

遍历IOC容器中所有bean

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 5][]

判断是否有@Controller和@RequestMapping注解

![20190725150640602.png][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 6][]

![20190725150947905.png][] ![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 7][]

![20190725152051990.png][]

### DispatcherServlet的初始化过程 ###

调用链关系如下图:

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 8][]

1.  HttpServletBean  init ()方法
2.  FrameworkServlet initServletBean方法→  initWebApplicationContext();
3.  DispatcherServlet onRefresh方法→  initStrategies()方法

容器启动时, 在HttpServletBean类里面的init方法里面进行初始化

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 9][]

最终执行DispatcherServlet的initStrategies方法进行组件的初始化

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 10][]

初始化上传文件解析器(或者是多部分请求解析器)

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 11][]

初始化本地化解析器

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 12][]

初始化主题解析器

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 13][] 初始化处理器映射器

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 14][]

初始化处理器适配器

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 15][]

初始化处理器异常解析器![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 16][]

初始化请求到视图名翻译器

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 17][]

初始化视图解析器![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 18][]

初始化重定向数据管理器

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 19][]

### DispatcherServlet的处理逻辑 ###

虽然HTTP1.1报文头一共有八种，常用的：GET、POST、PUT、DELETE，不太常用的：HEAD、TRACE、CONNECT、OPTIONS，但是实际上FrameworkServlet并没有实现CONNECT和HEAD。他们分别对应着doXXX（）方法。   
对于不同的方法，Spring统一的将他们引入到processRequest方法中，该方法完成了以下操作：

1.  提取当前线程的LocaleContext和RequestAttribute以便在当前请求后还能够恢复 
2.  根据当前request创建LocaleContext和RequestAttribute，并绑定到当前线程 
3.  委托doService方法执行doDispatch(request, response)方法

仍然是准备工作，将webApplicationContext，localeResolver等属性注入request中，然后继续由doDispatch方法进行处理，

**doDispatch方法的处理逻辑为： **  
第一步：将MultipartContent类的request转化为MultipartHttpServletRequest类型的request   
第二步：首先获取到HandlerExecutionChain，HandlerExecutionChain结构很简单，包括一个我们具体处理请求的Controller层方法的对象handler，以及拦截器interceptors、interceptorList。如果没有获取到相应的HandlerExecutionChain，则会返回404。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 20][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 21][]  
![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 22][]

第三步：若如果没有找到对应的Handler则通过response向用户报错

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 23][]  
第四步：根据当前的Handler寻找对应的HandlerAdapter（遍历寻找）

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 24][]  
第五步：缓存处理，根据Last-Modified缓存机制（第一次成功请求后如果在第二次请求之间内容没有改变，那么返回304状态码），Controller需要实现LastModified接口

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 25][]  
第六步：顺序调用拦截器的preHandle()方法，如果不符合拦截器的拦截规则则会同时调用afterCompletion()方法

![20190725142521102.png][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 26][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 27][]  
第七步：逻辑处理，通过适配器中转调用Handler（处理用户定义的逻辑）并返回视图

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 28][]  
第八步：调用拦截器的postHandle()

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 29][]   
第九步：调用processDispatchResult()对请求结果进行处理。如果业务处理过程中有异常抛出，调用processHandlerException()对异常进行处理，这里会调用我们自定义的HandlerExceptionResolvers进行处理，然后返回一个异常处理结果的ModelAndView对象。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 30][]

第十步:执行拦截器afterCompletion方法

![20190725145351971.png][]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70]: /images/20211122/df6c62bb04504617bbe56483d7f97609.png
[20190725103522813.png]: /images/20211122/751759cf0bc94672a2be20b397c6806a.png
[2019072510401179.png]: /images/20211122/8b4aa6e322a343a2aadac027d9a45167.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 1]: /images/20211122/3153e2c39bae4b279e27131cad08a0aa.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 2]: /images/20211122/2a09d1c976b645879a72de681e6b31d7.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 3]: /images/20211122/4a808bc8bdc944deb3b90fe2e6ffdc61.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 4]: /images/20211122/1a22ac4a778c4529b9f378a088f8686a.png
[20190725150307129.png]: /images/20211122/0f5cf180e0c642fc94fa15dfbe79aa7d.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 5]: /images/20211122/6f195bc274be492186e4b92116655caa.png
[20190725150640602.png]: /images/20211122/a5adf1ec57b342a9b967777509c55c67.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 6]: /images/20211122/1c964a211cac43f08085a80013854239.png
[20190725150947905.png]: https://img-blog.csdnimg.cn/20190725150947905.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 7]: /images/20211122/ed66395ef6fc4e56a0a1f43ecb3d628e.png
[20190725152051990.png]: /images/20211122/e8830c863110466e86a772241c978a85.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 8]: /images/20211122/6ad5b1cb57d9401099cc964428d4cd15.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 9]: /images/20211122/5d73f254b76b487ea0da5bb45154f3f9.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 10]: /images/20211122/ff39907952df42379948b195461f5a91.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 11]: /images/20211122/16e89b1f15504b188d6b4864ad6ad609.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 12]: /images/20211122/6f0ede95ce2b408fa8be23eea4500138.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 13]: /images/20211122/7256af0396e1474fbf59d8917203c0f7.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 14]: /images/20211122/4e36489c70a241c6b35342bf5e01d9c4.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 15]: /images/20211122/a9b325d1540a42ac8dab4c7a4a738090.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 16]: /images/20211122/e27be0299cd849d3959541184ca99409.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 17]: /images/20211122/4eb04ce1b39e4d4ab60771f5c7108f50.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 18]: /images/20211122/a97ff5c281714b7da38f5b0f0f0bda0c.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 19]: /images/20211122/8ffab30bd394454f82cdd554e07ca853.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 20]: /images/20211122/6330a3bde22c40ee925b4d26e7da19e7.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 21]: /images/20211122/2f79906595234195933d185097d297f8.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 22]: /images/20211122/df70894342b84c4e88ae95f5fc767bb5.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 23]: /images/20211122/7e9c8ccdaee34eadb576bde9a651789c.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 24]: /images/20211122/781c1dfefe8746c09aa052189e443ac1.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 25]: /images/20211122/afef94d36e4f47d7a247074f93804862.png
[20190725142521102.png]: /images/20211122/33898912a7ba4e3780d54df24dd91412.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 26]: /images/20211122/110b8ff0d97848f299b8266f9c8d9073.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 27]: /images/20211122/02af29c104704c21ade5e51ba292de97.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 28]: /images/20211122/cab0ca04c9684907beb2620abb84bcd7.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 29]: /images/20211122/b4c0d6694963418fbd3a51efe0fac024.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MjcwMTA2_size_16_color_FFFFFF_t_70 30]: /images/20211122/0941b17c5956467e9a3b02c5b661126e.png
[20190725145351971.png]: /images/20211122/108d2ff0048843e9bf476a9fc0a5e64d.png