本篇将涉及,通过本篇可以对整个springmvc模块有一个清晰的视角,在日常开发中可以快速定位问题和源码
主要完成以下工作:
主要完成以下工作:
在这一步中,分为两个阶段:
先来看一下其类关系图
SourceFilteringListener作为EventListener的实现类,在servlet的ApplicationContext初始化后,将收到事件回调完成剩余的初始化工作
protected void initStrategies(ApplicationContext context) { initMultipartResolver(context); initLocaleResolver(context); initThemeResolver(context); initHandlerMappings(context); initHandlerAdapters(context); initHandlerExceptionResolvers(context); initRequestToViewNameTranslator(context); initViewResolvers(context); initFlashMapManager(context); }
在这些初始化方法中,注册到spring容器中的bean由注解@EnableWebMVC导入。
导入工作委托给了DelegatingWebMvcConfiguration类
以上就是springMVC的初始化过程的整体脉络
整个过程相对比较复杂,整个逻辑在DispatcherServlet#doDispatcher方法中实现,该方法内部将具体工作委托给了RequestMappingHandlerMapping、HandlerExcutionChain、RequestMappingHandlerAdapter、ViewResolver、View等几个核心类来完成任务。
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception { HttpServletRequest processedRequest = request; HandlerExecutionChain mappedHandler = null; boolean multipartRequestParsed = false; WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request); try { ModelAndView mv = null; Exception dispatchException = null; try { processedRequest = checkMultipart(request); multipartRequestParsed = (processedRequest != request); // Determine handler for the current request. // 获取HandlerExcutionChain mappedHandler = getHandler(processedRequest); if (mappedHandler == null || mappedHandler.getHandler() == null) { noHandlerFound(processedRequest, response); return; } // 获取HandlerAdapter // Determine handler adapter for the current request. 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()) { logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified); } if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) { return; } } // 调用拦截器前置处理 if (!mappedHandler.applyPreHandle(processedRequest, response)) { return; } // 真正调用HandlerMethod(即Controller方法),内部涉及了参数解析(处理@RequestParams、@PathVariables注解原理)、参数类型转换、HandlerMethod执行结果处理(@ResponseBody注解原理)这几个步骤。后面内容我们详细剖析这个函数的内部机制 // Actually invoke the handler. mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); if (asyncManager.isConcurrentHandlingStarted()) { return; } applyDefaultViewName(processedRequest, mv); // 调用拦截器后置处理 mappedHandler.applyPostHandle(processedRequest, response, mv); } catch (Exception ex) { dispatchException = ex; } catch (Throwable err) { // As of 4.3, we're processing Errors thrown from handler methods as well, // making them available for @ExceptionHandler methods and other scenarios. dispatchException = new NestedServletException("Handler dispatch failed", err); } // 处理结果,涉及到视图渲染 processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException); } catch (Exception ex) { triggerAfterCompletion(processedRequest, response, mappedHandler, ex); } catch (Throwable err) { triggerAfterCompletion(processedRequest, response, mappedHandler, new NestedServletException("Handler processing failed", err)); } finally { if (asyncManager.isConcurrentHandlingStarted()) { // Instead of postHandle and afterCompletion if (mappedHandler != null) { mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response); } } else { // Clean up any resources used by a multipart request. if (multipartRequestParsed) { cleanupMultipart(processedRequest); } } } }
具体寻找过程的代码细节如下:
protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception { List<Match> matches = new ArrayList<Match>(); List<T> directPathMatches = this.mappingRegistry.getMappingsByUrl(lookupPath); if (directPathMatches != null) { addMatchingMappings(directPathMatches, matches, request); } if (matches.isEmpty()) { // No choice but to go through all mappings... // 如果没有找到,则遍历所有Controller方法。这里会涉及到Ant风格解析。O(n)的时间复杂度。效率极低 // 在使用路径参数@PathVariables的时候,会进入到这段逻辑 addMatchingMappings(this.mappingRegistry.getMappings().keySet(), matches, request); } if (!matches.isEmpty()) { Comparator<Match> comparator = new MatchComparator(getMappingComparator(request)); Collections.sort(matches, comparator); if (logger.isTraceEnabled()) { logger.trace("Found " + matches.size() + " matching mapping(s) for [" + lookupPath + "] : " + matches); } Match bestMatch = matches.get(0); if (matches.size() > 1) { if (CorsUtils.isPreFlightRequest(request)) { return PREFLIGHT_AMBIGUOUS_MATCH; } Match secondBestMatch = matches.get(1); if (comparator.compare(bestMatch, secondBestMatch) == 0) { Method m1 = bestMatch.handlerMethod.getMethod(); Method m2 = secondBestMatch.handlerMethod.getMethod(); throw new IllegalStateException("Ambiguous handler methods mapped for HTTP path '" + request.getRequestURL() + "': {" + m1 + ", " + m2 + "}"); } } // 设置属性到ServletHttpRequest实例中,在解析@PathVariables时使用 handleMatch(bestMatch.mapping, lookupPath, request); return bestMatch.handlerMethod; } else { return handleNoMatch(this.mappingRegistry.getMappings().keySet(), lookupPath, request); } }
protected void handleMatch(RequestMappingInfo info, String lookupPath, HttpServletRequest request) { super.handleMatch(info, lookupPath, request); String bestPattern; Map<String, String> uriVariables; Map<String, String> decodedUriVariables; Set<String> patterns = info.getPatternsCondition().getPatterns(); if (patterns.isEmpty()) { bestPattern = lookupPath; uriVariables = Collections.emptyMap(); decodedUriVariables = Collections.emptyMap(); } else { bestPattern = patterns.iterator().next(); // 使用Ant风格解析路径参数 uriVariables = getPathMatcher().extractUriTemplateVariables(bestPattern, lookupPath); decodedUriVariables = getUrlPathHelper().decodePathVariables(request, uriVariables); } request.setAttribute(BEST_MATCHING_PATTERN_ATTRIBUTE, bestPattern); request.setAttribute(HandlerMapping.URI_TEMPLATE_VARIABLES_ATTRIBUTE, decodedUriVariables); if (isMatrixVariableContentAvailable()) { Map<String, MultiValueMap<String, String>> matrixVars = extractMatrixVariables(request, uriVariables); request.setAttribute(HandlerMapping.MATRIX_VARIABLES_ATTRIBUTE, matrixVars); } if (!info.getProducesCondition().getProducibleMediaTypes().isEmpty()) { Set<MediaType> mediaTypes = info.getProducesCondition().getProducibleMediaTypes(); request.setAttribute(PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE, mediaTypes); } }
主要是通过HandlerMethodArgumentResolverComposite这个特殊的HandlerMethodArgumentResolver聚合了多个HandlerMethodArgumentResolver来解析参数、其内部将调用RequestParamMethodArgumentResolver、PathVariableMapMethodArgumentResolver等来处理参数解析逻辑
主要是通过HandlerMethodReturnValueHandlerComposite这个特殊的HandlerMethodReturnValueHandler聚合了多个HandlerMethodReturnValueHandler来处理返回结果,其内部将调用RequestResponseBodyMethodProcessor处理@ResponseBody、@RestController标记的方法和类来完成RESTful接口的结果返回
以上就是整个springmvc的工作流程,包括了初始化、请求处理两个步骤。在请求处理的过程中又涉及到了参数解析、参数类型转换、返回结果处理这些流程。由于整个代码比较繁多,这里就不列举所有的流程(视图渲染、异常处理这些细节)通过本篇的主体流程图可以快速定位到具体的代码。后续有需要查看更多细节可参考本篇快速定位