之前也已經總述過：AOP執行原理、SpringMvc執行流程，但總覺的有些點說的含糊不清，後續就把含糊不清的點，細緻的講解一下。現在先說請求核心處理doDispatch()方法。
上圖是默認容器啓動後IOC裝載的：HandlerAdapters和HandlerMapping（有印象，後續用）。
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);
//1. 獲取handler執行器鏈HandlerExecutionChain.
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null) {
noHandlerFound(processedRequest, response);
return;
}
//2. 獲取目標handler適配器HandlerAdapter執行目標Handler
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
String method = request.getMethod();
boolean isGet = "GET".equals(method);
if (isGet || "HEAD".equals(method)) {
long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
return;
}
}
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
//3. 執行目標Handler,返回ModelAndView.
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
applyDefaultViewName(processedRequest, mv);
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
catch (Exception ex) {
dispatchException = ex;
}
catch (Throwable err) {
dispatchException = new NestedServletException("Handler dispatch failed", err);
}
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()) {
if (mappedHandler != null) {
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
}
}
else {
if (multipartRequestParsed) {
cleanupMultipart(processedRequest);
}
}
}
}
圖中標的1-3，就是我們常說的主要執行流程。根據mvc執行圖，腦海中會有簡單清晰的執行流程。但現在主要闡述這三步具體的執行流程：
1. mappingHandler = getHandler(processedRequest);
DispatcherServlet.java中: 遍歷已經裝載的默認的HandlerMaping
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;
}
AbstractHandlerMapping.java中: 查找目標Handler，並添加攔截器。(給HandlerExecuterChain中 [private List<HandlerInterceptor> interceptorList;] 屬性賦值)
public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
Object handler = getHandlerInternal(request); <-----
if (handler == null) {
handler = getDefaultHandler();
}
if (handler == null) {
return null;
}
if (handler instanceof String) {
String handlerName = (String) handler;
handler = obtainApplicationContext().getBean(handlerName);
}
HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
if (logger.isTraceEnabled()) {
logger.trace("Mapped to " + handler);
}
else if (logger.isDebugEnabled() && !request.getDispatcherType().equals(DispatcherType.ASYNC)) {
logger.debug("Mapped to " + executionChain.getHandler());
}
if (CorsUtils.isCorsRequest(request)) {
CorsConfiguration globalConfig = this.corsConfigurationSource.getCorsConfiguration(request);
CorsConfiguration handlerConfig = getCorsConfiguration(handler, request);
CorsConfiguration config = (globalConfig != null ? globalConfig.combine(handlerConfig) : handlerConfig);
executionChain = getCorsHandlerExecutionChain(request, executionChain, config);
}
return executionChain;
}
AbstractHandlerMethodMapping.java中: 根據uri查找目標Handler方法。（給HandlerExecuterChain中 [private final Object handler;] 屬性賦值）
@Override
protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception {
String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);
this.mappingRegistry.acquireReadLock();
try {
HandlerMethod handlerMethod = lookupHandlerMethod(lookupPath, request);
return (handlerMethod != null ? handlerMethod.createWithResolvedBean() : null);
}
finally {
this.mappingRegistry.releaseReadLock();
}
}
2. HandlerAdapter ha = getHandlerAdapter(mappingHandler.getHandler());
DispatcherServlet.java中： 遍歷裝載的HandlerAdapter（開頭debug容器裝載圖），獲取支持當前handler的HandlerAdapter.
protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
if (this.handlerAdapters != null) {
for (HandlerAdapter adapter : this.handlerAdapters) {
if (adapter.supports(handler)) {
return adapter;
}
}
}
throw new ServletException("No adapter for handler [" + handler +
"]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");
}
3. mv = ha.handler(processedRequest,response,mappingHandler.getHandler());
1. AbstactHandlerMappingAdapter.java中: (HandlerAdapter類圖： xxxHandlerAdapter extends AbstactHandlerMappingAdapter implements HandlerAdapter)
public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {
return handleInternal(request, response, (HandlerMethod) handler); <---------
}
2. RequestMappingHandlerAdapter.java中：
protected ModelAndView handleInternal(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ModelAndView mav;
checkRequest(request);
//檢測是否需要加鎖執行synchronize
if (this.synchronizeOnSession) {
HttpSession session = request.getSession(false);
if (session != null) {
//Spring自帶的WebUtils工具類
Object mutex = WebUtils.getSessionMutex(session);
synchronized (mutex) {
mav = invokeHandlerMethod(request, response, handlerMethod);
}
}else {
mav = invokeHandlerMethod(request, response, handlerMethod);
}
}else {
mav = invokeHandlerMethod(request, response, handlerMethod); <----------
}
if (!response.containsHeader(HEADER_CACHE_CONTROL)) {
if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);
}
else {
prepareResponse(response);
}
}
return mav;
}
3. RequestMappingHandlerAdapter.java中：（doDispatch()上面挑選的HandlerMappingAdapter） 對於mv這步，暫時不講述
protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ServletWebRequest webRequest = new ServletWebRequest(request, response);
try {
WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);
//主要看這個類的動作
ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
if (this.argumentResolvers != null) {
invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
}
if (this.returnValueHandlers != null) {
invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
}
invocableMethod.setDataBinderFactory(binderFactory);
invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);
ModelAndViewContainer mavContainer = new ModelAndViewContainer();
mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
modelFactory.initModel(webRequest, mavContainer, invocableMethod);
mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);
AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response);
asyncWebRequest.setTimeout(this.asyncRequestTimeout);
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
asyncManager.setTaskExecutor(this.taskExecutor);
asyncManager.setAsyncWebRequest(asyncWebRequest);
asyncManager.registerCallableInterceptors(this.callableInterceptors);
asyncManager.registerDeferredResultInterceptors(this.deferredResultInterceptors);
if (asyncManager.hasConcurrentResult()) {
Object result = asyncManager.getConcurrentResult();
mavContainer = (ModelAndViewContainer) asyncManager.getConcurrentResultContext()[0];
asyncManager.clearConcurrentResult();
LogFormatUtils.traceDebug(logger, traceOn -> {
String formatted = LogFormatUtils.formatValue(result, !traceOn);
return "Resume with async result [" + formatted + "]";
});
invocableMethod = invocableMethod.wrapConcurrentResult(result);
}
invocableMethod.invokeAndHandle(webRequest, mavContainer); <------------
if (asyncManager.isConcurrentHandlingStarted()) {
return null;
}
return getModelAndView(mavContainer, modelFactory, webRequest);
}
finally {
webRequest.requestCompleted();
}
}
4. ServletInvocableHandlerMethod.java : 調用該方法並通過已配置的方法之一處理返回值(ServletInvocableHandlerMethod extends InvocableHandlerMethod)
public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
//執行方法，返回結果，或許再根據已註冊的HandlerMethodReturnValueHandler解析
Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs); <------------
setResponseStatus(webRequest);
if (returnValue == null) {
if (isRequestNotModified(webRequest) || getResponseStatus() != null || mavContainer.isRequestHandled()) {
mavContainer.setRequestHandled(true);
return;
}
}else if (StringUtils.hasText(getResponseStatusReason())) {
mavContainer.setRequestHandled(true);
return;
}
mavContainer.setRequestHandled(false);
Assert.state(this.returnValueHandlers != null, "No return value handlers");
try {
this.returnValueHandlers.handleReturnValue(
returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
}
catch (Exception ex) {
if (logger.isTraceEnabled()) {
logger.trace(formatErrorForReturnValue(returnValue), ex);
}
throw ex;
}
}
5. InvocableHandlerMethod.java :
public Object invokeForRequest(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
//參數解析,將url中的參數值解析
Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);
if (logger.isTraceEnabled()) {
logger.trace("Arguments: " + Arrays.toString(args));
}
//利用JavaReflect完成方法調用
return doInvoke(args);
}
6. InvocableHandlerMethod.java :
protected Object[] getMethodArgumentValues(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
MethodParameter[] parameters = getMethodParameters();
Object[] args = new Object[parameters.length];
for (int i = 0; i < parameters.length; i++) {
MethodParameter parameter = parameters[i];
parameter.initParameterNameDiscovery(this.parameterNameDiscoverer);
args[i] = resolveProvidedArgument(parameter, providedArgs);
if (args[i] != null) {
continue;
}
//檢測、使用參數解析器HandlerMethodArgumentResolver解析參數
if (this.argumentResolvers.supportsParameter(parameter)) {
try {
args[i] = this.argumentResolvers.resolveArgument(
parameter, mavContainer, request, this.dataBinderFactory);
continue;
}catch (Exception ex) {
// Leave stack trace for later, e.g. AbstractHandlerExceptionResolver
if (logger.isDebugEnabled()) {
String message = ex.getMessage();
if (message != null && !message.contains(parameter.getExecutable().toGenericString())) {
logger.debug(formatArgumentError(parameter, message));
}
}
throw ex;
}
}
if (args[i] == null) {
throw new IllegalStateException(formatArgumentError(parameter, "No suitable resolver"));
}
}
return args;
}
整個流程貌似可以說的通，再屢一下，很容易發現，沒有對已經裝載的參數解析器，進行遍歷的代碼。
真的沒有嗎？
再去看一下最後InvocableHandlerMethod.getMethodArgumentValues()方法，其中有段代碼有檢測的
是否支持已裝載的參數解析器：if(this.argumentResolvers.supportsParameter(parameter))。順着
這條再去看一下InvocableHandlerMethod類中argumentResolvers屬性類型，會發現是使用混合模型的
對象：HandlerMethodArgumentResolverComposite argumentResolvers。這樣很容易發現，遍歷參數解
析器的操作是在HandlerMethodArgumentResolverCompoiste中執行。
private HandlerMethodArgumentResolver getArgumentResolver(MethodParameter parameter) {
//這個argumentResolverCache，是優化請求處理，使用的緩存：Map<MethodParameter, HandlerMethodArgumentResolver>
HandlerMethodArgumentResolver result = this.argumentResolverCache.get(parameter);
if (result == null) {
for (HandlerMethodArgumentResolver methodArgumentResolver : this.argumentResolvers) {
if (methodArgumentResolver.supportsParameter(parameter)) {
result = methodArgumentResolver;
this.argumentResolverCache.put(parameter, result);
break;
}
}
}
return result;
}
HandlerAdapter：（HandlerAdapter子類需要實現HandlerAdapter接口，並實現supports(Object handler)方法，而supports()方法返回boolean類型，決定了當前HandlerAdapter是否支持使用。）
RequestMappingHandlerAdapter： handler方法使用@RequestMapping、@Controller等註解
SimpleControllerHandlerAdapter： handler類實現Controller接口
HttpRequestHandlerAdapter：handler類實現HttpRequetHandler接口
HandlerMapping：（上面已經截圖）
HandlerMethodArgumentResolver：RequestMappingHandlerAdapter.getDefaultArgumentResolvers()。
參考文章： https://www.cnblogs.com/w-y-c-m/p/8443892.html
//默認的參數解析，創建了默認的24個參數解析器，並添加至resolvers
//這裏的24個參數解析器都是針對不同的參數類型來解析的
private List<HandlerMethodArgumentResolver> getDefaultArgumentResolvers() {
List<HandlerMethodArgumentResolver> resolvers = new ArrayList<HandlerMethodArgumentResolver>();
// 基於註解的參數解析器
//一般用於帶有@RequestParam註解的簡單參數綁定，簡單參數比如byte、int、long、double、String以及對應的包裝類型
resolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory(), false));
//用於處理帶有@RequestParam註解，且參數類型爲Map的解析綁定
resolvers.add(new RequestParamMapMethodArgumentResolver());
//一般用於處理帶有@PathVariable註解的默認參數綁定
resolvers.add(new PathVariableMethodArgumentResolver());
//也是用於帶有@PathVariable註解的Map相關參數綁定，後續還有一些默認的參數解析器。後續還有一些參數解析器，我這裏都不一一解釋了。想具體確認某個參數會交個哪個參數解析器處理，可以通過以下解析器的supportsParameter(MethodParameter parameter)方法得知
resolvers.add(new PathVariableMapMethodArgumentResolver());
resolvers.add(new MatrixVariableMethodArgumentResolver());
resolvers.add(new MatrixVariableMapMethodArgumentResolver());
resolvers.add(new ServletModelAttributeMethodProcessor(false));
resolvers.add(new RequestResponseBodyMethodProcessor(getMessageConverters()));
resolvers.add(new RequestPartMethodArgumentResolver(getMessageConverters()));
resolvers.add(new RequestHeaderMethodArgumentResolver(getBeanFactory()));
resolvers.add(new RequestHeaderMapMethodArgumentResolver());
resolvers.add(new ServletCookieValueMethodArgumentResolver(getBeanFactory()));
resolvers.add(new ExpressionValueMethodArgumentResolver(getBeanFactory()));
// 基於類型的參數解析器
resolvers.add(new ServletRequestMethodArgumentResolver());
resolvers.add(new ServletResponseMethodArgumentResolver());
resolvers.add(new HttpEntityMethodProcessor(getMessageConverters()));
resolvers.add(new RedirectAttributesMethodArgumentResolver());
resolvers.add(new ModelMethodProcessor());
resolvers.add(new MapMethodProcessor());
resolvers.add(new ErrorsMethodArgumentResolver());
resolvers.add(new SessionStatusMethodArgumentResolver());
resolvers.add(new UriComponentsBuilderMethodArgumentResolver());
// Custom arguments
if (getCustomArgumentResolvers() != null) {
resolvers.addAll(getCustomArgumentResolvers());
}
// Catch-all
resolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory(), true));
resolvers.add(new ServletModelAttributeMethodProcessor(true));
return resolvers;
}
常見使用場景：SpringBoot中implement WebMvcConfigurer具體實現相關配置
1. 攔截器Interceptor
2. 參數解析器HandlerMethodArgumentResolver
&3.消息轉換器MessageConverters
流程體會：
1. 父類接口、抽象類、實現類： 模板設計模型
2. 混合設計模式： 參考 HandlerMethodArgumentResolverComposite （實現父類方法，並設置父類集合作爲屬性）
3. Spring中自帶的一些工具類的使用
