SpringMVC 源码剖析
0 从源码角度分析SpringMVC执行流程
public class DispatcherServlet extends FrameworkServlet { protected void doDispatch ( HttpServletRequest request, HttpServletResponse response) throws Exception { HandlerExecutionChain mappedHandler = getHandler ( request) ; HandlerAdapter ha = getHandlerAdapter ( mappedHandler. getHandler ( ) ) ; if ( ! mappedHandler. applyPreHandle ( processedRequest, response) ) { return ; } mv = ha. handle ( processedRequest, response, mappedHandler. getHandler ( ) ) ; mappedHandler. applyPostHandle ( processedRequest, response, mv) ; processDispatchResult ( processedRequest, response, mappedHandler, mv, dispatchException) ; } private void processDispatchResult ( HttpServletRequest request, HttpServletResponse response, @Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv, @Nullable Exception exception) throws Exception { render ( mv, request, response) ; mappedHandler. triggerAfterCompletion ( request, response, null ) ; } protected void render ( ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception { View view = resolveViewName ( viewName, mv. getModelInternal ( ) , locale, request) ; view. render ( mv. getModelInternal ( ) , request, response) ; } protected View resolveViewName ( String viewName, @Nullable Map < String , Object > model, Locale locale, HttpServletRequest request) throws Exception { ViewResolver viewResolver; View view = viewResolver. resolveViewName ( viewName, locale) ; }
}
public interface ViewResolver { View resolveViewName ( String viewName, Locale locale) throws Exception ;
}
public interface View { void render ( @Nullable Map < String , ? > model, HttpServletRequest request, HttpServletResponse response) throws Exception ;
}
1 关于根据请求获取处理器执行链
分析这一行代码:
HandlerExecutionChain mappedHandler = getHandler ( request) ; 1. HandlerExecutionChain :处理器执行链对象2. HandlerExecutionChain 中的属性:public class HandlerExecutionChain { Object handler = new HandlerMethod ( . . . . . ) ; List < HandlerInterceptor > interceptorList; } 3. HandlerMethod 是什么?HandlerMethod 是最核心的要执行的目标,翻译为:处理器方法。注意:HandlerMethod 是在web服务器启动时初始化spring容器的时候,就创建好了。这个类当中比较重要的属性包括:beanName和Method 例如,以下代码:@Controller ( "userController" ) public class UserController { @RequestMapping ( "/login" ) public String login ( User user) { return . . . . } } 那么以上代码对应了一个HandlerMethod 对象:public class HandlerMethod { private String beanName = "userController" ; private Method loginMethod; } 4. getHandler ( request) ; 这个方法还是在DispatcherServlet 类中。protected HandlerExecutionChain getHandler ( HttpServletRequest request) throws Exception { if ( this . handlerMappings != null ) { for ( HandlerMapping mapping : this . handlerMappings) { HandlerExecutionChain handler = mapping. getHandler ( request) ; if ( handler != null ) { return handler; } } } return null ; } 重点:我们处理请求的第一步代码是:HandlerExecutionChain mappedHandler = getHandler ( request) ; 其本质上是调用了:HandlerExecutionChain handler = mapping. getHandler ( request) ; mapping变量就是 HandlerMapping 。HandlerMapping 是一个接口:翻译为处理器映射器,专门负责映射的。就是本质上根据请求路径去映射处理器方法的。HandlerMapping 接口下有很多实现类:例如其中一个比较有名的,常用的:RequestMappingHandlerMapping 这个 RequestMappingHandlerMapping 叫做:@RequestMapping 注解专用的处理器映射器对象。当然,如果你没有使用 @RequestMapping 注解,也可以写xml配置文件来进行映射,那个时候对应的就是其他的HandlerMapping 接口的实现类了。HandlerMapping 对象也是在服务器启动阶段创建的,所有的HandlerMapping 对象都是在服务器启动阶段创建,并且存放到集合中。public class DispatcherServlet { List < HandlerMapping > handlerMappings; } 5. RequestMappingHandlerMapping 中的 getHandler ( request) ; HandlerExecutionChain handler = mapping. getHandler ( request) ; mapping. getHandler ( request) ; 这个方法底层一定是获取了 HandlerMethod 对象,将其赋值给 HandlerExecutionChain 的handler属性public class RequestMappingHandlerMapping extends AbstractHandlerMethodMapping { protected void registerHandlerMethod ( Object handler, Method method, RequestMappingInfo mapping) { super . registerHandlerMethod ( handler, method, mapping) ; updateConsumesCondition ( mapping, method) ; } } public class AbstractHandlerMethodMapping { protected void registerHandlerMethod ( Object handler, Method method, T mapping) { this . mappingRegistry. register ( mapping, handler, method) ; } public void register ( T mapping, Object handler, Method method) { HandlerMethod handlerMethod = createHandlerMethod ( handler, method) ; } protected HandlerMethod createHandlerMethod ( Object handler, Method method) { if ( handler instanceof String beanName) { return new HandlerMethod ( beanName, obtainApplicationContext ( ) . getAutowireCapableBeanFactory ( ) , obtainApplicationContext ( ) , method) ; } return new HandlerMethod ( handler, method) ; } } 这一步牵连到的类有哪些:HandlerExecutionChain HandlerMethod HandlerInterceptor HandlerMapping RequestMappingHandlerMapping (是HandlerMaping 接口的实现)
2 关于根据处理器来获取处理器适配器
分析:
HandlerAdapter ha = getHandlerAdapter ( mappedHandler. getHandler ( ) ) ; 1. 底层使用了适配器模式。2. 每一个处理器( 我们自己写的Controller ) ,都有自己适合的处理器适配器。3. 在SpringMVC 当中处理器适配器也有很多种,其中一个比较有名的,常用的处理器适配器是:RequestMappingHandlerAdapter
这个处理器适配器是专门处理 “处理器方法”上有 @RequestMapping 注解的。4. mappedHandler. getHandler ( ) 获取的是 HandlerMethod 对象5. HandlerAdapter 也是一个接口:其中有一个常用的实现类:RequestMappingHandlerAdapter 6. 在服务器启动阶段,所有的 HandlerAdapter 接口的实现类都会创建出来。在服务器启动阶段!!!!!!List < HandlerAdapter > handlerAdapters; 7. HandlerAdapter 接口非常重要,通过这个接口来调用最终的 HandlerMethod 。8. HandlerAdapter 是适配器,是对 HandlerMethod 进行的适配。9. 在DispatcherServlet 类中,如下代码:protected HandlerAdapter getHandlerAdapter ( Object handler) throws ServletException { if ( this . handlerAdapters != null ) { for ( HandlerAdapter adapter : this . handlerAdapters) { if ( adapter. supports ( handler) ) { return adapter; } } } }
3 关于执行请求对应的拦截器preHandle
关于执行请求对应的拦截器的preHandle方法DispatcherServlet :
if ( ! mappedHandler. applyPreHandle ( processedRequest, response) ) { return ;
} HandlerExecutionChain :
boolean applyPreHandle ( HttpServletRequest request, HttpServletResponse response) throws Exception { for ( int i = 0 ; i < this . interceptorList. size ( ) ; i++ ) { HandlerInterceptor interceptor = this . interceptorList. get ( i) ; if ( ! interceptor. preHandle ( request, response, this . handler) ) { triggerAfterCompletion ( request, response, null ) ; return false ; } this . interceptorIndex = i; } return true ;
} 遍历List 集合,从List 集合中取出每一个 HandlerInterceptor 对象,调用 preHandle,i++ ,可见是顺序调用。
4 关于调用处理器方法
关于调用处理器方法:mv = ha. handle ( processedRequest, response, mappedHandler. getHandler ( ) ) ; ha 是处理器适配器mv 是ModelAndView 对象这个方法是最核心的,调用请求路径对应的HandlerMethod 。(调用处理器方法。)ha是HandlerAdapter ,如果是 @RequestMapping 注解对应的,那么就是 RequestMappingHandlerAdapter :RequestMappingHandlerAdapter :protected ModelAndView handleInternal ( HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod) throws Exception { mav = invokeHandlerMethod ( request, response, handlerMethod) ; } protected ModelAndView invokeHandlerMethod ( HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod) throws Exception { WebDataBinderFactory binderFactory = getDataBinderFactory ( handlerMethod) ; ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod ( handlerMethod) ; invocableMethod. setDataBinderFactory ( binderFactory) ; invocableMethod. setParameterNameDiscoverer ( this . parameterNameDiscoverer) ; invocableMethod. invokeAndHandle ( webRequest, mavContainer) ; } 在HandlerAdapter 中做的核心事情:将前端提交的form数据通过 HttpMessageConverter 将其转换成 POJO 对象。(数据转换)并将数据绑定到 HandlerMethod 对象上。调用HandlerMethod 。返回 ModelAndView
5 关于执行请求对应的拦截器的postHandle
DispatcherServlet : mappedHandler. applyPostHandle ( processedRequest, response, mv) ; HandlerExecutionChain : void applyPostHandle ( HttpServletRequest request, HttpServletResponse response, @Nullable ModelAndView mv) throws Exception { for ( int i = this . interceptorList. size ( ) - 1 ; i >= 0 ; i-- ) { HandlerInterceptor interceptor = this . interceptorList. get ( i) ; interceptor. postHandle ( request, response, this . handler, mv) ; } } 通过源码解决,可以很轻松的看到,从List 集合中逆序( i-- ) 逐一取出拦截器对象,并且调用拦截器的 postHandle方法。
6 关于处理分发结果
public class DispatcherServlet { processDispatchResult ( processedRequest, response, mappedHandler, mv, dispatchException) ; private void processDispatchResult ( HttpServletRequest request, HttpServletResponse response, @Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv, @Nullable Exception exception) throws Exception { render ( mv, request, response) ; } protected void render ( ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception { View view = resolveViewName ( viewName, mv. getModelInternal ( ) , locale, request) ; view. render ( mv. getModelInternal ( ) , request, response) ; } protected View resolveViewName ( String viewName, @Nullable Map < String , Object > model, Locale locale, HttpServletRequest request) throws Exception { ViewResolver viewResolver; View view = viewResolver. resolveViewName ( viewName, locale) ; }
}
public interface ViewResolver { View resolveViewName ( String viewName, Locale locale) throws Exception ;
}
public interface View { void render ( @Nullable Map < String , ? > model, HttpServletRequest request, HttpServletResponse response) throws Exception ;
}
7 关于执行拦截器的afterCompletion方法
DispatcherServlet : private void processDispatchResult ( HttpServletRequest request, HttpServletResponse response, @Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv, @Nullable Exception exception) throws Exception { render ( mv, request, response) ; mappedHandler. triggerAfterCompletion ( request, response, null ) ; } HandlerExecutionChain : void triggerAfterCompletion ( HttpServletRequest request, HttpServletResponse response, @Nullable Exception ex) { for ( int i = this . interceptorIndex; i >= 0 ; i-- ) { HandlerInterceptor interceptor = this . interceptorList. get ( i) ; try { interceptor. afterCompletion ( request, response, this . handler, ex) ; } catch ( Throwable ex2) { logger. error ( "HandlerInterceptor.afterCompletion threw exception" , ex2) ; } } } 通过源码可以看出,也是通过逆序( i-- ) 的方式进行拦截器的调用,调用拦截器的afterCompletion方法。