SpringMvc源码-RequestMappingHandlerAdapter

HandlerAdapter接口的说明

在SprintMVC中，HandlerAdapter组件是一个handler适配器类，它通过handle方法调用request对应的controller方法来处理请求【HandlerMethod】

 /**
 * Use the given handler to handle this request.
 * The workflow that is required may vary widely.
 * @param request current HTTP request
 * @param response current HTTP response
 * @param handler handler to use. This object must have previously been passed
 * to the {@code supports} method of this interface, which must have 实际上是 HandlerMethod
 * returned {@code true}.
 * @throws Exception in case of errors
 * @return a ModelAndView object with the name of the view and the required
 * model data, or {@code null} if the request has been handled directly
 */
 //
 @Nullable
ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception;

如何获取HandlerAdapter

见DispatcherServlet.getHandlerAdapter

protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
	//遍历DipatcherServlet.properties里org.springframework.web.servlet.HandlerAdapter的配置，调用handlerAdpater.supports看那个符合条件
	//Springboot中，会执行RequestMappingHandler.supports-->AbstractHandlerMethodAdapter.supports 即handler是HandlerMetod
	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");
}

handle方法的执行

调用路径是AbstractHandlerMethodAdapter.handle()–>AbstractHandlerMethodAdapter.handleInternal()–>RequestMappingHandlerAdapter.handleInternal。

见RequestMappingHandlerAdapter.handleInternal

@Override
protected ModelAndView handleInternal(HttpServletRequest request,
		HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {

	ModelAndView mav;
	//校验requestMethod和requireSession
	checkRequest(request);

	// Execute invokeHandlerMethod in synchronized block if required.
	// session线程不安全，如果想用户多次请求都访问同一个session需要加一个全局锁。。性能极差很少见
	if (this.synchronizeOnSession) {
		HttpSession session = request.getSession(false);
		if (session != null) {
			Object mutex = WebUtils.getSessionMutex(session);
			synchronized (mutex) {
				mav = invokeHandlerMethod(request, response, handlerMethod);
			}
		}
		else {
			// No HttpSession available -> no mutex necessary
			mav = invokeHandlerMethod(request, response, handlerMethod);
		}
	}
	else {
		// No synchronization on session demanded at all...
		// 关键方法，代理方法执行handlerMethod,返回modelAndView
		mav = invokeHandlerMethod(request, response, handlerMethod);
	}

	if (!response.containsHeader(HEADER_CACHE_CONTROL)) {
		if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
			applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);
		}
		else {
			prepareResponse(response);
		}
	}

	return mav;
}

controller方法的执行原理，代理模式和反射的应用：invokeHandlerMethod

最终的执行实际上是利用了java的反射包，以及代理模式，关键代码见：invokeHandlerMethod

/**
 * Invoke the {@link RequestMapping} handler method preparing a {@link ModelAndView}
 * if view resolution is required.
 * @since 4.2
 * @see #createInvocableHandlerMethod(HandlerMethod)
 */
@Nullable
protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
		HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
	//HttpServletRequest 的封装
	ServletWebRequest webRequest = new ServletWebRequest(request, response);
	try {
		//用来处理request中的参数映射，WebDataBinderFactory里的值见：afterPropertiesSet
		WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
		//用来创建初始化model
		ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);
		//根据handlerMethod实例化一个ServletInvocableHandlerMethod来处理请求
		ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
		//设置argumentResolvers处理request的参数 argumentResolvers里的值见afterPropertiesSet
		if (this.argumentResolvers != null) {
			invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
		}
		//设置argumentResolvers处理response的参数 returnValueHandlers里的值见afterPropertiesSet
		// 可自定义 TODO 比如想给所有的ResponseBody返回值封装成{code:0,msg:1,data:null}
		if (this.returnValueHandlers != null) {
			invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
		}
		invocableMethod.setDataBinderFactory(binderFactory);
		invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);

		//modelAndView的上下文对象
		ModelAndViewContainer mavContainer = new ModelAndViewContainer();
		mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
		//初始化Model对象，同时将sessionAtrributes值和ModelAtrributes的值都合并在一起放在Model中
		modelFactory.initModel(webRequest, mavContainer, invocableMethod);
		mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);

		//todo 未读
		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);
		}

		//关键代码，通过handlerMethod的代理方法，执行Controller的方法，将结果存储到mavContainer
		invocableMethod.invokeAndHandle(webRequest, mavContainer);
		if (asyncManager.isConcurrentHandlingStarted()) {
			return null;
		}

		//获取ModelAndView
		return getModelAndView(mavContainer, modelFactory, webRequest);
	}
	finally {
		webRequest.requestCompleted();
	}
}

invocableMethod.invokeAndHandle(webRequest, mavContainer);

public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
		Object... providedArgs) throws Exception {

	//关键代码，通过java的反射机制doInvoke执行handlerMethod对应的controller方法
	Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
	setResponseStatus(webRequest);

	if (returnValue == null) {
		if (isRequestNotModified(webRequest) || getResponseStatus() != null || mavContainer.isRequestHandled()) {
			disableContentCachingIfNecessary(webRequest);
			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 {
		//调用returnValueHandlers 将返回值写到response中（webRequest.getNativeResponse)里
		// 由于现在开发采用前后端分离，RestApi往往会用到RequestResponseBodyMethodProcessor，可以看这个类，返回值和controller方法有@ResponseBody
		this.returnValueHandlers.handleReturnValue(
				returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
	}
	catch (Exception ex) {
		if (logger.isTraceEnabled()) {
			logger.trace(formatErrorForReturnValue(returnValue), ex);
		}
		throw ex;
	}
}

invokeForRequest方法

@Nullable
public Object invokeForRequest(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
		Object... providedArgs) throws Exception {
	//从request里获取controller执行方法的参数，request里的值变为方法里设置的参数
	Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);
	if (logger.isTraceEnabled()) {
		logger.trace("Arguments: " + Arrays.toString(args));
	}
	//通过java的反射机制，执行controller里的方法，方法参数getMethodArgumentValues获取
	return doInvoke(args);
}

protected Object doInvoke(Object... args) throws Exception {
	ReflectionUtils.makeAccessible(getBridgedMethod());
	try {
		//todo 通过反射执行方法 书签
		//调用java反射包的invoke 代理执行HandlerMethod里econtroller对应的方法
		// getBridgedMethod= 如果没有意外等于controller被执行的方法
		// getBean()=Controller对象
		// args=request通过argumentResolver得到的方法参数对象
		return getBridgedMethod().invoke(getBean(), args);
	}
	catch (IllegalArgumentException ex) {
		assertTargetBean(getBridgedMethod(), getBean(), args);
		String text = (ex.getMessage() != null ? ex.getMessage() : "Illegal argument");
		throw new IllegalStateException(formatInvokeError(text, args), ex);
	}
	catch (InvocationTargetException ex) {
		// Unwrap for HandlerExceptionResolvers ...
		Throwable targetException = ex.getTargetException();
		if (targetException instanceof RuntimeException) {
			throw (RuntimeException) targetException;
		}
		else if (targetException instanceof Error) {
			throw (Error) targetException;
		}
		else if (targetException instanceof Exception) {
			throw (Exception) targetException;
		}
		else {
			throw new IllegalStateException(formatInvokeError("Invocation failure", args), targetException);
		}
	}
}