一个东西用久了，自然就会从仅使用的层面上升到探究其原理的层面，在javaweb中springmvc更是如此，越是优秀的框架，其底层实现代码更是复杂，而在我看来，一个优秀程序猿就相当于一名武林高手，不断进阶武功秘籍，越是高深莫测的功夫，越是要探究其原理，而springmvc就是一本十分深奥的武功秘籍。
说起拦截器，说不得不和过滤器进行对比，在此贴图一张不进行多加解释，简单的来说拦截器能作用于controller层方法实现的前后而过滤器不能。
在这里先列出一个简单的controller层的实现
正常访问之后我们看看控制台
我们都知道DispatcherServlet是所谓前端控制器，是整个Springmvc的入口，但是这个前端控制器里面又有许多门，我们都看过箱子里面装着又一个箱子，跟这种感觉差不多。
DispatcherServlet里面执行处理入口的方法是doService，先看源码
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
if(this.logger.isDebugEnabled()) {
String attributesSnapshot = WebAsyncUtils.getAsyncManager(request).hasConcurrentResult()?" resumed":"";
this.logger.debug("DispatcherServlet with name \'" + this.getServletName() + "\'" + attributesSnapshot + " processing " + request.getMethod() + " request for [" + getRequestUri(request) + "]");
}
HashMap attributesSnapshot1 = null;
if(WebUtils.isIncludeRequest(request)) {
attributesSnapshot1 = new HashMap();
Enumeration inputFlashMap = request.getAttributeNames();
label108:
while(true) {
String attrName;
do {
if(!inputFlashMap.hasMoreElements()) {
break label108;
}
attrName = (String)inputFlashMap.nextElement();
} while(!this.cleanupAfterInclude && !attrName.startsWith("org.springframework.web.servlet"));
attributesSnapshot1.put(attrName, request.getAttribute(attrName));
}
}
request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.getWebApplicationContext());
request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver);
request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver);
request.setAttribute(THEME_SOURCE_ATTRIBUTE, this.getThemeSource());
FlashMap inputFlashMap1 = this.flashMapManager.retrieveAndUpdate(request, response);
if(inputFlashMap1 != null) {
request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, Collections.unmodifiableMap(inputFlashMap1));
}
request.setAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE, new FlashMap());
request.setAttribute(FLASH_MAP_MANAGER_ATTRIBUTE, this.flashMapManager);
try {
this.doDispatch(request, response);
} finally {
if(!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted() && attributesSnapshot1 != null) {
this.restoreAttributesAfterInclude(request, attributesSnapshot1);
}
}
}
由于主要是先分析拦截器，doservice的其他部分就先不解释，先看一段代码
this.logger.debug("DispatcherServlet with name \'" + this.getServletName() + "\'" + attributesSnapshot + " processing " + request.getMethod() + " request for [" + getRequestUri(request) + "]");
这段跟我贴出的控制台信息截图的第一段信息是不是很相似，由此可以证明，doService的确是执行处理方法的入口。但是doService并没有直接进行处理，而是交给了doDispatch进行具体的处理。下面的doDispatch的源码
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception { HttpServletRequest processedRequest = request; HandlerExecutionChain mappedHandler = null; boolean multipartRequestParsed = false; WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request); try { try { ModelAndView err = null; Exception dispatchException = null; try { processedRequest = this.checkMultipart(request); multipartRequestParsed = processedRequest != request; mappedHandler = this.getHandler(processedRequest); if(mappedHandler == null || mappedHandler.getHandler() == null) { this.noHandlerFound(processedRequest, response); return; } HandlerAdapter ex = this.getHandlerAdapter(mappedHandler.getHandler()); String method = request.getMethod(); boolean isGet = "GET".equals(method); if(isGet || "HEAD".equals(method)) { long lastModified = ex.getLastModified(request, mappedHandler.getHandler()); if(this.logger.isDebugEnabled()) { this.logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified); } if((new ServletWebRequest(request, response)).checkNotModified(lastModified) && isGet) { return; } } if(!mappedHandler.applyPreHandle(processedRequest, response)) { return; } err = ex.handle(processedRequest, response, mappedHandler.getHandler()); if(asyncManager.isConcurrentHandlingStarted()) { return; } this.applyDefaultViewName(request, err); mappedHandler.applyPostHandle(processedRequest, response, err); } catch (Exception var19) { dispatchException = var19; } this.processDispatchResult(processedRequest, response, mappedHandler, err, dispatchException); } catch (Exception var20) { this.triggerAfterCompletion(processedRequest, response, mappedHandler, var20); } catch (Error var21) { this.triggerAfterCompletionWithError(processedRequest, response, mappedHandler, var21); } } finally { if(asyncManager.isConcurrentHandlingStarted()) { if(mappedHandler != null) { mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response); } } else if(multipartRequestParsed) { this.cleanupMultipart(processedRequest); } } }
那么问题来了，既然我发出的请求是转发到doDispatch进行具体请求，那么请求和Controller层之间是怎么联系上的，我们再来看看控制层的信息