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:HandlerExecutionChainHandlerMethodHandlerInterceptorHandlerMappingRequestMappingHandlerMapping(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:RequestMappingHandlerAdapter6. 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。