<SpringMVC源码分析(1)标签解析>:介绍了解析过程中,初始化若干组件。
<SpringMVC源码分析(2)DispatcherServlet的初始化>:初始化DispatcherServlet的多个组件。
本文继续分析DispatcherServlet解析请求的过程。
概览
①:DispatcherServlet是springmvc中的前端控制器(front controller),负责接收request并将request转发给对应的处理组件.
②:HanlerMapping是springmvc中完成url到controller映射的组件.DispatcherServlet接收request,然后从HandlerMapping查找处理request的controller.
③:Cntroller处理request,并返回ModelAndView对象,Controller是springmvc中负责处理request的组件(类似于struts2中的Action),ModelAndView是封装结果视图的组件.
④ ⑤ ⑥:视图解析器解析ModelAndView对象并返回对应的视图给客户端.
要点
- 维护url和controller的映射
这部分工作由DefaultAnnotationHandlerMapping.setApplicationContext的父类
org.springframework.web.servlet.handler.AbstractDetectingUrlHandlerMapping.initApplicationContext实现。具体方法为detectHandlers
protected void detectHandlers() throws BeansException { if (logger.isDebugEnabled()) { logger.debug("Looking for URL mappings in application context: " + getApplicationContext()); } String[] beanNames = (this.detectHandlersInAncestorContexts ? BeanFactoryUtils.beanNamesForTypeIncludingAncestors(getApplicationContext(), Object.class) : getApplicationContext().getBeanNamesForType(Object.class)); // Take any bean name that we can determine URLs for. for (String beanName : beanNames) { String[] urls = determineUrlsForHandler(beanName); if (!ObjectUtils.isEmpty(urls)) { // URL paths found: Let‘s consider it a handler. registerHandler(urls, beanName); } else { if (logger.isDebugEnabled()) { logger.debug("Rejected bean name ‘" + beanName + "‘: no URL paths identified"); } } } }
2.准确定位处理请求的具体方法(在AnnotationMethodHandlerAdapter中实现)
protected ModelAndView invokeHandlerMethod(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { ServletHandlerMethodResolver methodResolver = getMethodResolver(handler); Method handlerMethod = methodResolver.resolveHandlerMethod(request);//具体实现方法的匹配 ServletHandlerMethodInvoker methodInvoker = new ServletHandlerMethodInvoker(methodResolver); ServletWebRequest webRequest = new ServletWebRequest(request, response); ExtendedModelMap implicitModel = new BindingAwareModelMap(); Object result = methodInvoker.invokeHandlerMethod(handlerMethod, handler, webRequest, implicitModel); ModelAndView mav = methodInvoker.getModelAndView(handlerMethod, handler.getClass(), result, implicitModel, webRequest); methodInvoker.updateModelAttributes(handler, (mav != null ? mav.getModel() : null), implicitModel, webRequest); return mav; }
1.请求入口
@Override protected final void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { processRequest(request, response); } /** * Delegate POST requests to {@link #processRequest}. * @see #doService */ @Override protected final void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { processRequest(request, response); } protected final void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { long startTime = System.currentTimeMillis(); Throwable failureCause = null; // Expose current LocaleResolver and request as LocaleContext. LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext(); LocaleContextHolder.setLocaleContext(buildLocaleContext(request), this.threadContextInheritable); // Expose current RequestAttributes to current thread. RequestAttributes previousRequestAttributes = RequestContextHolder.getRequestAttributes(); ServletRequestAttributes requestAttributes = null; if (previousRequestAttributes == null || previousRequestAttributes.getClass().equals(ServletRequestAttributes.class)) { requestAttributes = new ServletRequestAttributes(request); RequestContextHolder.setRequestAttributes(requestAttributes, this.threadContextInheritable); } if (logger.isTraceEnabled()) { logger.trace("Bound request context to thread: " + request); } try { doService(request, response); } catch (ServletException ex) { failureCause = ex; throw ex; } catch (IOException ex) { failureCause = ex; throw ex; } catch (Throwable ex) { failureCause = ex; throw new NestedServletException("Request processing failed", ex); } finally { // Clear request attributes and reset thread-bound context. LocaleContextHolder.setLocaleContext(previousLocaleContext, this.threadContextInheritable); if (requestAttributes != null) { RequestContextHolder.setRequestAttributes(previousRequestAttributes, this.threadContextInheritable); requestAttributes.requestCompleted(); } if (logger.isTraceEnabled()) { logger.trace("Cleared thread-bound request context: " + request); } if (failureCause != null) { this.logger.debug("Could not complete request", failureCause); } else { this.logger.debug("Successfully completed request"); } if (this.publishEvents) { // Whether or not we succeeded, publish an event. long processingTime = System.currentTimeMillis() - startTime; this.webApplicationContext.publishEvent( new ServletRequestHandledEvent(this, request.getRequestURI(), request.getRemoteAddr(), request.getMethod(), getServletConfig().getServletName(), WebUtils.getSessionId(request), getUsernameForRequest(request), processingTime, failureCause)); } } }
processRequest方法主要做4项工作。
- 得到当前线程的LocaleContext和RequestAttributes,创建新的LocaleContext和RequestAttributes并重新绑定到当前线程。
- 调用子类实现的doService()
- 重置当前线程的LocaleContext和RequestAttributes
- 执行成功后,发布ServletRequestHandledEvent事件。
2.DispatcherServlet自定义的doService方法
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception { if (logger.isDebugEnabled()) { String requestUri = urlPathHelper.getRequestUri(request); logger.debug("DispatcherServlet with name ‘" + getServletName() + "‘ processing " + request.getMethod() + " request for [" + requestUri + "]"); } // Keep a snapshot of the request attributes in case of an include, // to be able to restore the original attributes after the include. Map<String, Object> attributesSnapshot = null; if (WebUtils.isIncludeRequest(request)) { logger.debug("Taking snapshot of request attributes before include"); attributesSnapshot = new HashMap<String, Object>(); Enumeration attrNames = request.getAttributeNames(); while (attrNames.hasMoreElements()) { String attrName = (String) attrNames.nextElement(); if (this.cleanupAfterInclude || attrName.startsWith("org.springframework.web.servlet")) { attributesSnapshot.put(attrName, request.getAttribute(attrName)); } } } // Make framework objects available to handlers and view objects. request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, getWebApplicationContext()); request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver); request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver); request.setAttribute(THEME_SOURCE_ATTRIBUTE, getThemeSource()); try { doDispatch(request, response); } finally { // Restore the original attribute snapshot, in case of an include. if (attributesSnapshot != null) { restoreAttributesAfterInclude(request, attributesSnapshot); } } }
主要做两部分工作
- 如果是include请求,先保存一份request域数据的快照,doDispatch执行过后,将会用快照数据恢复。
- 调用doDispatch方法,完成请求转发。
3.doDispatch方法
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception { HttpServletRequest processedRequest = request; HandlerExecutionChain mappedHandler = null; int interceptorIndex = -1; try { ModelAndView mv; boolean errorView = false; try { // 1.检查是否是文件上传的请求 processedRequest = checkMultipart(request); // Determine handler for the current request. // 2.取得处理当前请求的controller,这里也称为hanlder,处理器,第一个步骤的意义就在这里体现了. //这里并不是直接返回controller,而是返回的HandlerExecutionChain请求处理器链对象,该对象封装了handler和interceptors. mappedHandler = getHandler(processedRequest, false); if (mappedHandler == null || mappedHandler.getHandler() == null) { noHandlerFound(processedRequest, response); return; } // Determine handler adapter for the current request. //3. 获取处理request的处理器适配器handler adapter HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler()); // Process last-modified header, if supported by the handler. String method = request.getMethod(); boolean isGet = "GET".equals(method); if (isGet || "HEAD".equals(method)) { long lastModified = ha.getLastModified(request, mappedHandler.getHandler()); if (logger.isDebugEnabled()) { String requestUri = urlPathHelper.getRequestUri(request); logger.debug("Last-Modified value for [" + requestUri + "] is: " + lastModified); } if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) { return; } } // Apply preHandle methods of registered interceptors. // 4.拦截器的预处理方法 HandlerInterceptor[] interceptors = mappedHandler.getInterceptors(); if (interceptors != null) { for (int i = 0; i < interceptors.length; i++) { HandlerInterceptor interceptor = interceptors[i]; if (!interceptor.preHandle(processedRequest, response, mappedHandler.getHandler())) { triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, null); return; } interceptorIndex = i; } } // Actually invoke the handler. // 5.实际的处理器处理请求,返回结果视图对象 mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); // Do we need view name translation? if (mv != null && !mv.hasView()) { mv.setViewName(getDefaultViewName(request)); } // Apply postHandle methods of registered interceptors. // 6.拦截器的后处理方法 if (interceptors != null) { for (int i = interceptors.length - 1; i >= 0; i--) { HandlerInterceptor interceptor = interceptors[i]; interceptor.postHandle(processedRequest, response, mappedHandler.getHandler(), mv); } } } catch (ModelAndViewDefiningException ex) { logger.debug("ModelAndViewDefiningException encountered", ex); mv = ex.getModelAndView(); } catch (Exception ex) { Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null); mv = processHandlerException(processedRequest, response, handler, ex); errorView = (mv != null); } // Did the handler return a view to render? if (mv != null && !mv.wasCleared()) { render(mv, processedRequest, response); if (errorView) { WebUtils.clearErrorRequestAttributes(request); } } else { if (logger.isDebugEnabled()) { logger.debug("Null ModelAndView returned to DispatcherServlet with name ‘" + getServletName() + "‘: assuming HandlerAdapter completed request handling"); } } // Trigger after-completion for successful outcome. triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, null); } catch (Exception ex) { // Trigger after-completion for thrown exception. triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, ex); throw ex; } catch (Error err) { ServletException ex = new NestedServletException("Handler processing failed", err); // Trigger after-completion for thrown exception. triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, ex); throw ex; } finally { // Clean up any resources used by a multipart request. if (processedRequest != request) { cleanupMultipart(processedRequest); } } }
很明显这儿是SpringMVC核心。
1.根据请求的路径找到HandlerMethod(带有Method反射属性,也就是对应Controller中的方法)(DispatcherServlet.getHandler完成)
2.匹配路径对应的拦截器(DispatcherServlet.getHandler完成)
3.获得HandlerExecutionChain对象(DispatcherServlet.getHandler完成)
4.通过HandlerAdapter对象进行处理得到ModelAndView对象(HandlerAdapter.handle)
5.调用HandlerInterceptor.preHandle
6.调用HandlerInterceptor.postHandle
7. 渲染
4.总结
简单粗暴的总结下
step1-6: 获取controller
step5-15 :调用controller方法
step17-20:渲染view
其他:aop方式处理拦截统一处理。