前言
因?yàn)镠andler格式是不固定的，所以在處理請(qǐng)求時(shí)需要HandlerAdapter做適配，我們?cè)賮?lái)回顧下HandlerAdapter的定義。
public interface HandlerAdapter {
/**
* 判斷是否支持傳入的handler
*/
boolean supports(Object handler);
/**
* 使用給定的handler處理請(qǐng)求
*/
ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception;
/**
* 返回上次修改時(shí)間，可以返回-1表示不支持
*/
long getLastModified(HttpServletRequest request, Object handler);
}
HandlerAdapter的實(shí)現(xiàn)有HttpRequestHandlerAdapter、SimpleServletHandlerAdapter、SimpleControllerHandlerAdapter、AnnotationMethodHandlerAdapter(已廢棄)和RequestMappingHandlerAdapter，今天我們主要來(lái)分析下RequestMappingHandlerAdapter，因?yàn)镽equestMappingHandlerAdapter使用的最多，其余的幾個(gè)比較簡(jiǎn)單。
RequestMappingHandlerAdapter是和RequestMappingHandlerMapping配合使用的，我們先來(lái)看一下RequestMappingHandlerAdapter的繼承關(guān)系圖，然后再詳細(xì)分析。
AbstractHandlerMethodAdapter
supports方法
AbstractHandlerMethodAdapter實(shí)現(xiàn)了supports方法，可以看出支持的Handler是HandlerMethod，另外還附加了一個(gè)判斷方法supportsInternal，這個(gè)方法由RequestMappingHandlerAdapter實(shí)現(xiàn)，其就是簡(jiǎn)單地返回true。
public final boolean supports(Object handler) {
return (handler instanceof HandlerMethod && supportsInternal((HandlerMethod) handler));
}
protected boolean supportsInternal(HandlerMethod handlerMethod) {
return true;
}
handle方法
AbstractHandlerMethodAdapter實(shí)現(xiàn)了handle方法，就是簡(jiǎn)單地調(diào)用了模板方法handleInternal，handleInternal方法由RequestMappingHandlerAdapter實(shí)現(xiàn)。
public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {
return handleInternal(request, response, (HandlerMethod) handler);
}
RequestMappingHandlerAdapter
初始化過(guò)程
RequestMappingHandlerAdapter實(shí)現(xiàn)了InitializingBean接口，所以它的初始化入口是afterPropertiesSet方法。
public void afterPropertiesSet() {
// Do this first, it may add ResponseBody advice beans
initControllerAdviceCache();
if (this.argumentResolvers == null) {
List<HandlerMethodArgumentResolver> resolvers = getDefaultArgumentResolvers();
this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
}
if (this.initBinderArgumentResolvers == null) {
List<HandlerMethodArgumentResolver> resolvers = getDefaultInitBinderArgumentResolvers();
this.initBinderArgumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
}
if (this.returnValueHandlers == null) {
List<HandlerMethodReturnValueHandler> handlers = getDefaultReturnValueHandlers();
this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);
}
}
可以看出主要是初始化了三個(gè)對(duì)象
- argumentResolvers 用于給處理器方法和被@ModelAttribute注解的方法設(shè)置參數(shù)
- initBinderArgumentResolvers 用于給被@InitBinder注解的方法設(shè)置參數(shù)
- returnValueHandlers 用于將處理器返回值處理成ModelAndView類型
這里面又涉及了兩個(gè)組件HandlerMethodArgumentResolver和HandlerMethodReturnValueHandler，這里我們不會(huì)具體深入的分析這兩個(gè)組件，以后專門(mén)做講解。
使用過(guò)程
從上面的分析我們知道使用的入口是handleInternal方法，可以看出最重要的一句是invokeHandlerMethod。
protected ModelAndView handleInternal(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ModelAndView mav;
// 檢查HttpMethod是否支持，檢查是否需要session
checkRequest(request);
// 需要同步session
if (this.synchronizeOnSession) {
HttpSession session = request.getSession(false);
if (session != null) {
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;
}
下面我們來(lái)具體看下invokeHandlerMethod
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);
ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
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();
invocableMethod = invocableMethod.wrapConcurrentResult(result);
}
invocableMethod.invokeAndHandle(webRequest, mavContainer);
if (asyncManager.isConcurrentHandlingStarted()) {
return null;
}
return getModelAndView(mavContainer, modelFactory, webRequest);
} finally {
webRequest.requestCompleted();
}
}
這個(gè)方法非常復(fù)雜，我們先來(lái)解釋下幾個(gè)變量
WebDataBinderFactory 從名字就可以看出來(lái)是創(chuàng)建WebDataBinder用的，WebDataBinder用于參數(shù)綁定，主要用于參數(shù)與String之間的類型轉(zhuǎn)換。
ModelFactory 用來(lái)處理Model，主要包含兩個(gè)功能，1. 在Handler處理之前對(duì)Model初始化，2. 請(qǐng)求結(jié)束以后對(duì)Model參數(shù)進(jìn)行更新
ServletInvocableHandlerMethod 它繼承自HandlerMethod，并且可以直接執(zhí)行，實(shí)際請(qǐng)求的處理就是通過(guò)它來(lái)執(zhí)行的，參數(shù)綁定、處理請(qǐng)求以及返回值的處理都在里面完成
這三個(gè)變量創(chuàng)建完之后的工作還有三步（省略異步處理）：
新建傳遞參數(shù)的ModelAndViewContainer容器，并將相應(yīng)的參數(shù)設(shè)置到Model中
執(zhí)行請(qǐng)求
invocableMethod.invokeAndHandle(webRequest, mavContainer);
3.請(qǐng)求完成后進(jìn)行一些后置處理 getModelAndView(mavContainer, modelFactory, webRequest);
public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
// 處理請(qǐng)求
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);
try {
// 使用ReturnValueHandler處理返回值
this.returnValueHandlers.handleReturnValue(
returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
} catch (Exception ex) {
throw ex;
}
}
public Object invokeForRequest(NativeWebRequest request, ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
// 處理得到方法參數(shù)
Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);
// 調(diào)用方法處理請(qǐng)求
Object returnValue = doInvoke(args);
return returnValue;
}
// org.springframework.web.method.support.InvocableHandlerMethod
private Object[] getMethodArgumentValues(NativeWebRequest request, 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;
}
// 使用ArgumentResolver處理參數(shù)
if (this.argumentResolvers.supportsParameter(parameter)) {
try {
args[i] = this.argumentResolvers.resolveArgument(
parameter, mavContainer, request, this.dataBinderFactory);
continue;
} catch (Exception ex) {
throw ex;
}
}
if (args[i] == null) {
throw new IllegalStateException("Could not resolve method parameter at index " +
parameter.getParameterIndex() + " in " + parameter.getMethod().toGenericString() +
": " + getArgumentResolutionErrorMessage("No suitable resolver for", i));
}
}
return args;
}
