spring mvc主流程原始碼閱讀（剖析）
阿新 • • 發佈：2019-06-26
第一步，通過web.xml的配置可以知道，使用者訪問url第一次先走到DispatchServlet，（預設你學過基本的java的Servlet開發）
<servlet> <servlet-name>springServlet</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> <init-param> <param-name>contextConfigLocation</param-name> <param-value>/WEB-INF/spring-mvc.xml</param-value> </init-param> <load-on-startup>1</load-on-startup> </servlet>
DispatchServlet類重點閱讀
//初始化HandlerMap
private void initHandlerMappings(ApplicationContext context) {
this.handlerMappings = null;
if (this.detectAllHandlerMappings) {
Map<String, HandlerMapping> matchingBeans = BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
if (!matchingBeans.isEmpty()) {
//解析xml的 對映關係後，存放到 handlerMapping 後面會用到
this.handlerMappings = new ArrayList(matchingBeans.values());
OrderComparator.sort(this.handlerMappings);
}
} else {
try {
HandlerMapping hm = (HandlerMapping)context.getBean("handlerMapping", HandlerMapping.class);
this.handlerMappings = Collections.singletonList(hm);
} catch (NoSuchBeanDefinitionException var3) {
;
}
}
if (this.handlerMappings == null) {
this.handlerMappings = this.getDefaultStrategies(context, HandlerMapping.class);
if (this.logger.isDebugEnabled()) {
this.logger.debug("No HandlerMappings found in servlet '" + this.getServletName() + "': using default");
}
}
}下圖為斷點觀察效果
從上圖看到，其實這個map就是從spring-mvc.xml檔案中讀取的不同型別的對映，標準對映、靜態資源、攔截器對映等
//初始化Adapters
private void initHandlerAdapters(ApplicationContext context) {
this.handlerAdapters = null;
if (this.detectAllHandlerAdapters) {
Map<String, HandlerAdapter> matchingBeans = BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerAdapter.class, true, false);
if (!matchingBeans.isEmpty()) {
this.handlerAdapters = new ArrayList(matchingBeans.values());
OrderComparator.sort(this.handlerAdapters);
}
} else {
try {
HandlerAdapter ha = (HandlerAdapter)context.getBean("handlerAdapter", HandlerAdapter.class);
this.handlerAdapters = Collections.singletonList(ha);
} catch (NoSuchBeanDefinitionException var3) {
;
}
}
if (this.handlerAdapters == null) {
this.handlerAdapters = this.getDefaultStrategies(context, HandlerAdapter.class);
if (this.logger.isDebugEnabled()) {
this.logger.debug("No HandlerAdapters found in servlet '" + this.getServletName() + "': using default");
}
}
}
然後，通過斷點+原始碼玩起來了，我這裡是通過一個介面測試的，
首先執行 doService方法
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
if (this.logger.isDebugEnabled()) {
String requestUri = urlPathHelper.getRequestUri(request);
String resumed = WebAsyncUtils.getAsyncManager(request).hasConcurrentResult() ? " resumed" : "";
this.logger.debug("DispatcherServlet with name '" + this.getServletName() + "'" + resumed + " processing " + request.getMethod() + " request for [" + requestUri + "]");
}
Map<String, Object> attributesSnapshot = null;
if (WebUtils.isIncludeRequest(request)) {
this.logger.debug("Taking snapshot of request attributes before include");
attributesSnapshot = new HashMap();
Enumeration attrNames = request.getAttributeNames();
label113:
while(true) {
String attrName;
do {
if (!attrNames.hasMoreElements()) {
break label113;
}
attrName = (String)attrNames.nextElement();
} while(!this.cleanupAfterInclude && !attrName.startsWith("org.springframework.web.servlet"));
attributesSnapshot.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 inputFlashMap = this.flashMapManager.retrieveAndUpdate(request, response);
if (inputFlashMap != null) {
request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, Collections.unmodifiableMap(inputFlashMap));
}
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()) {
return;
}
if (attributesSnapshot != null) {
this.restoreAttributesAfterInclude(request, attributesSnapshot);
}
}
}
做了一些判斷和資料的初始化工作，這裡不是核心邏輯就暫時跳過了，看
doDispatch方法
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;//關鍵變數，注意觀察
boolean multipartRequestParsed = false;
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
try {
try {
ModelAndView mv = null;
Exception dispatchException = null;
try {
processedRequest = this.checkMultipart(request);
multipartRequestParsed = processedRequest != request;
mappedHandler = this.getHandler(processedRequest, false);//額這裡無語了點了好幾層才找到最終獲取的Handler
if (mappedHandler == null || mappedHandler.getHandler() == null) {
this.noHandlerFound(processedRequest, response);
return;
}
HandlerAdapter ha = this.getHandlerAdapter(mappedHandler.getHandler());//獲取對應的adaptor
String method = request.getMethod();
boolean isGet = "GET".equals(method);
if (isGet || "HEAD".equals(method)) {
long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
if (this.logger.isDebugEnabled()) {
String requestUri = urlPathHelper.getRequestUri(request);
this.logger.debug("Last-Modified value for [" + requestUri + "] is: " + lastModified);
}
if ((new ServletWebRequest(request, response)).checkNotModified(lastModified) && isGet) {
return;
}
}
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
try {
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());//執行方法
} finally {
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
}
this.applyDefaultViewName(request, mv);
mappedHandler.applyPostHandle(processedRequest, response, mv);
} catch (Exception var28) {
dispatchException = var28;
}
this.processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
} catch (Exception var29) {
this.triggerAfterCompletion(processedRequest, response, mappedHandler, var29);
} catch (Error var30) {
this.triggerAfterCompletionWithError(processedRequest, response, mappedHandler, var30);
}
} finally {
if (asyncManager.isConcurrentHandlingStarted()) {
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
return;
} else {
if (multipartRequestParsed) {
this.cleanupMultipart(processedRequest);
}
}
}
}
獲取handler
handler封裝HandlerExecutionChain，從程式碼來看就是把攔截器相關資訊補充進去
protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {
HandlerExecutionChain chain = handler instanceof HandlerExecutionChain ? (HandlerExecutionChain)handler : new HandlerExecutionChain(handler);
chain.addInterceptors(this.getAdaptedInterceptors());
String lookupPath = this.urlPathHelper.getLookupPathForRequest(request);
Iterator i$ = this.mappedInterceptors.iterator();
while(i$.hasNext()) {
MappedInterceptor mappedInterceptor = (MappedInterceptor)i$.next();
if (mappedInterceptor.matches(lookupPath, this.pathMatcher)) {
chain.addInterceptor(mappedInterceptor.getInterceptor());
}
}
return chain;
}
從handlerMap中獲取Adaptors，
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
Iterator i$ = this.handlerMappings.iterator();
HandlerExecutionChain handler;
do {
if (!i$.hasNext()) {
return null;
}
HandlerMapping hm = (HandlerMapping)i$.next();
if (this.logger.isTraceEnabled()) {
this.logger.trace("Testing handler map [" + hm + "] in DispatcherServlet with name '" + this.getServletName() + "'");
}
handler = hm.getHandler(request);
} while(handler == null);
return handler;
}
執行adaptor，最後利用了反射執行代理類的方法
執行後的返回檢視邏輯
private ModelAndView getModelAndView(ModelAndViewContainer mavContainer, ModelFactory modelFactory, NativeWebRequest webRequest) throws Exception {
modelFactory.updateModel(webRequest, mavContainer);
if (mavContainer.isRequestHandled()) {
return null;
} else {
ModelMap model = mavContainer.getModel();
ModelAndView mav = new ModelAndView(mavContainer.getViewName(), model);
if (!mavContainer.isViewReference()) {
mav.setView((View)mavContainer.getView());
}
if (model instanceof RedirectAttributes) {
Map<String, ?> flashAttributes = ((RedirectAttributes)model).getFlashAttributes();
HttpServletRequest request = (HttpServletRequest)webRequest.getNativeRequest(HttpServletRequest.class);
RequestContextUtils.getOutputFlashMap(request).putAll(flashAttributes);
}
return mav;
}
}
總結：url->dispatchServlet->doService->doDispatch->根據url，從handlerMap獲取handler，然後根據handler獲取adaptor，通過adaptor執行要執行的方法，然後返回頁面或者介面資料（返回的邏輯沒來得及細看）
在這裡即使用到了工廠模式、代理模式