这一次搞懂SpringMVC原理

@

前言

前面几篇文章,学习了Spring IOC、Bean实例化过程、AOP、事务的源码和设计思想,了解了Spring的整体运行流程,但如果是web开发,那么必不可少的还有Spring MVC,本篇主要分析在请求调用过程中SpringMVC的实现原理,通过本篇要搞懂它是怎么解决请求、参数、返回值映射等问题的。

正文

请求入口

我们都知道前端调用后端接口时,都会通过Servlet进行转发,而Servlet的声明周期包含下面四个阶段:

  • 实例化(new)
  • 初始化(init)
  • 执行(service调用doGet/doPost)
  • 销毁(destroy)

前两个阶段在Spring启动阶段就做好了(init根据配置可能是第一次请求时才会调用),销毁是服务关闭的时候进行,本文主要分析的就是请求执行阶段。我们知道SpringMVC的核心就是DispatcherServlet,该类是对Servlet的扩展,所以直接从该类的service方法开始,但在此类中没有service方法,那肯定是在其父类中,我们先来看看其继承体系:
在这里插入图片描述
逐个往上找,在FrameworkServlet方法中就有一个service方法:

	protected void service(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		HttpMethod httpMethod = HttpMethod.resolve(request.getMethod());
		if (httpMethod == HttpMethod.PATCH || httpMethod == null) {
			processRequest(request, response);
		}
		else {
			super.service(request, response);
		}
	}

    protected void service(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException
    {
        String method = req.getMethod();

        if (method.equals(METHOD_GET)) {
            long lastModified = getLastModified(req);
            if (lastModified == -1) {
                doGet(req, resp);
            } else {
                long ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE);
                if (ifModifiedSince < lastModified) {
                    maybeSetLastModified(resp, lastModified);
                    doGet(req, resp);
                } else {
                    resp.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
                }
            }

        } else if (method.equals(METHOD_HEAD)) {
            long lastModified = getLastModified(req);
            maybeSetLastModified(resp, lastModified);
            doHead(req, resp);
        } else if (method.equals(METHOD_POST)) {
            doPost(req, resp);
        } else if (method.equals(METHOD_PUT)) {
            doPut(req, resp);
        } else if (method.equals(METHOD_DELETE)) {
            doDelete(req, resp);
        } else if (method.equals(METHOD_OPTIONS)) {
            doOptions(req,resp);
        } else if (method.equals(METHOD_TRACE)) {
            doTrace(req,resp);
        } else {
            String errMsg = lStrings.getString("http.method_not_implemented");
            Object[] errArgs = new Object[1];
            errArgs[0] = method;
            errMsg = MessageFormat.format(errMsg, errArgs);
            
            resp.sendError(HttpServletResponse.SC_NOT_IMPLEMENTED, errMsg);
        }
    }
   

但其主要还是调用父类HttpServlet中的方法,而该类又会根据不同的请求方式会调到子类中,最后的核心方法就是DispatcherServlet中的doDispatch方法:

	protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
		HttpServletRequest processedRequest = request;
		HandlerExecutionChain mappedHandler = null;
		boolean multipartRequestParsed = false;

		//异步管理
		WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

		try {
			ModelAndView mv = null;
			Exception dispatchException = null;

			try {
				//文件上传
				processedRequest = checkMultipart(request);
				multipartRequestParsed = (processedRequest != request);

				//这个方法很重要,重点看
				// Determine handler for the current request.
				mappedHandler = getHandler(processedRequest);
				if (mappedHandler == null) {
					noHandlerFound(processedRequest, response);
					return;
				}

				//获取跟HandlerMethod匹配的HandlerAdapter对象
				// Determine handler adapter for the current request.
				HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

				// Process last-modified header, if supported by the handler.
				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;
					}
				}

				//前置过滤器,如果为false则直接返回
				if (!mappedHandler.applyPreHandle(processedRequest, response)) {
					return;
				}

				//调用到Controller具体方法,核心方法调用,重点看看
				// Actually invoke the handler.
				mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

				if (asyncManager.isConcurrentHandlingStarted()) {
					return;
				}

				applyDefaultViewName(processedRequest, mv);

				//中置过滤器
				mappedHandler.applyPostHandle(processedRequest, response, mv);
			}
			catch (Exception ex) {
				dispatchException = ex;
			}
			catch (Throwable err) {
				// As of 4.3, we're processing Errors thrown from handler methods as well,
				// making them available for @ExceptionHandler methods and other scenarios.
				dispatchException = new NestedServletException("Handler dispatch failed", err);
			}

			//视图渲染及后置过滤器执行
			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()) {
				// Instead of postHandle and afterCompletion
				if (mappedHandler != null) {
					mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
				}
			}
			else {
				// Clean up any resources used by a multipart request.
				if (multipartRequestParsed) {
					cleanupMultipart(processedRequest);
				}
			}
		}
	}

MVC的所有处理逻辑都在这个方法中,先总结一下这个方法的实现逻辑,首先根据请求的url拿到缓存中的HandlerMethod对象和执行链对象,HandlerMethod中封装了controller对象、方法对象和方法参数等信息,执行链则是包含了一个个HandlerInterceptor拦截器;然后再通过HandlerMethod拿到对应的HandlerAdapter,这个对象的作用就是去适配我们的controller;准备工作做完后,首先会执行前置过滤,如果被拦截则直接返回,否则就去调用controller中的方法执行我们的业务逻辑并返回一个ModelView对象;接着执行中置过滤器,以及处理全局异常捕获器捕获到异常;最后进行视图渲染返回并执行后置过滤器进行资源释放等工作。
以上就是MVC的整体执行流程,下面就逐个来分析,首先进入getHandler方法:

	protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
		//handlerMappering实例
		if (this.handlerMappings != null) {
			for (HandlerMapping mapping : this.handlerMappings) {
				//获取HandlerMethod和过滤器链的包装类
				HandlerExecutionChain handler = mapping.getHandler(request);
				if (handler != null) {
					return handler;
				}
			}
		}
		return null;
	}

是委托给HandlerMapping对象的,这是一个接口,主要的实现类是RequestMappingHandlerMapping,同样先来看看其继承体系:
在这里插入图片描述
这个类是管理请求和处理类之间的映射关系的,你是否疑惑它是在哪里实例化的呢?下面先来看看MVC组件的初始化。

组件初始化

这里我以自动化配置的注解方式说明,Spring提供了一个@EnableWebMvc,通过前面的学习我们知道在这个注解中必定导入了一个配置类,点进去可以看到是DelegatingWebMvcConfiguration,这个类就是负责MVC的组件和扩展实现的初始化,其本身我们先不看,先看其父类WebMvcConfigurationSupport,这个类我们应该不陌生,要做一些自定义扩展时就需要继承该类(如拦截器Interceptor),同样作用的类还有WebMvcConfigurerAdapter,这个类是对前者相对安全的扩展,为什么是相对安全呢?因为继承前者会导致自动配置失效,而使用后者则不必担心此问题,只需要在类上加上@EnableWebMvc注解。
WebMvcConfigurationSupport中我们可以看到很多@Bean标注的方法,也就是mvc组件的实例化,这里主要看看requestMappingHandlerMapping,其余的可自行阅读理解,也就是一些Bean的注册:

	public RequestMappingHandlerMapping requestMappingHandlerMapping() {
		RequestMappingHandlerMapping mapping = createRequestMappingHandlerMapping();
		mapping.setOrder(0);
		mapping.setInterceptors(getInterceptors());
		mapping.setContentNegotiationManager(mvcContentNegotiationManager());
		mapping.setCorsConfigurations(getCorsConfigurations());

		......省略

		return mapping;
	}

这里主要看getInterceptors方法如何获取拦截器的:

	protected final Object[] getInterceptors() {
		if (this.interceptors == null) {
			InterceptorRegistry registry = new InterceptorRegistry();
			//钩子方法,需要自己定义
			addInterceptors(registry);
			registry.addInterceptor(new ConversionServiceExposingInterceptor(mvcConversionService()));
			registry.addInterceptor(new ResourceUrlProviderExposingInterceptor(mvcResourceUrlProvider()));
			this.interceptors = registry.getInterceptors();
		}
		return this.interceptors.toArray();
	}

第一次进来会调用addInterceptors添加拦截器,这是一个模板方法,在子类DelegatingWebMvcConfiguration中实现:

	private final WebMvcConfigurerComposite configurers = new WebMvcConfigurerComposite();
	
	protected void addInterceptors(InterceptorRegistry registry) {
		this.configurers.addInterceptors(registry);
	}

	public void addInterceptors(InterceptorRegistry registry) {
		for (WebMvcConfigurer delegate : this.delegates) {
			delegate.addInterceptors(registry);
		}
	}

可以看到最终是调用WebMvcConfigureraddInterceptors方法,也就是我们对WebMvcConfigurerAdapter的自定义扩展。看到这里我们应该明白了MVC的组件是如何添加到IOC容器中的,但是DispatcherServlet又是怎么获取到它们的呢?回到之前的代码中,在DispatcherServlet这个类中有一个onRefresh方法,这个方法又调用了initStrategies方法完成了MVC九大组件的注册:

	protected void onRefresh(ApplicationContext context) {
		initStrategies(context);
	}

	protected void initStrategies(ApplicationContext context) {
		initMultipartResolver(context);
		initLocaleResolver(context);
		initThemeResolver(context);
		initHandlerMappings(context);
		initHandlerAdapters(context);
		initHandlerExceptionResolvers(context);
		initRequestToViewNameTranslator(context);
		initViewResolvers(context);
		initFlashMapManager(context);
	}

	private void initHandlerMappings(ApplicationContext context) {
		this.handlerMappings = null;

		if (this.detectAllHandlerMappings) {
			// Find all HandlerMappings in the ApplicationContext, including ancestor contexts.
			Map<String, HandlerMapping> matchingBeans =
					BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
			if (!matchingBeans.isEmpty()) {
				this.handlerMappings = new ArrayList<>(matchingBeans.values());
				// We keep HandlerMappings in sorted order.
				AnnotationAwareOrderComparator.sort(this.handlerMappings);
			}
		}
		else {
			try {
				HandlerMapping hm = context.getBean(HANDLER_MAPPING_BEAN_NAME, HandlerMapping.class);
				this.handlerMappings = Collections.singletonList(hm);
			}
			catch (NoSuchBeanDefinitionException ex) {
				// Ignore, we'll add a default HandlerMapping later.
			}
		}
		
		if (this.handlerMappings == null) {
			this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);
		}
	}

initHandlerMappings为例,其它组件实现逻辑基本一样。首先从IOC容器中拿到handlerMappings的所有实现类(WebMvcConfigurationSupport中注入的对象就在这里被获取到),若没有,则从DispatcherServlet.properties配置文件中(这个配置在spring-webmvc工程下org/springframework/web/servlet/DispatcherServlet.properties)获取默认的配置:

org.springframework.web.servlet.LocaleResolver=org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver

org.springframework.web.servlet.ThemeResolver=org.springframework.web.servlet.theme.FixedThemeResolver

org.springframework.web.servlet.HandlerMapping=org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping,\
	org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping

org.springframework.web.servlet.HandlerAdapter=org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter,\
	org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter,\
	org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter

org.springframework.web.servlet.HandlerExceptionResolver=org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver,\
	org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver,\
	org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver

org.springframework.web.servlet.RequestToViewNameTranslator=org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator

org.springframework.web.servlet.ViewResolver=org.springframework.web.servlet.view.InternalResourceViewResolver

org.springframework.web.servlet.FlashMapManager=org.springframework.web.servlet.support.SessionFlashMapManager

但是onRefresh又是在什么时候调用的呢?有两个地方,一个是Servlet初始化时会调用到initWebApplicationContext进行容器的初始化,这个方法中就会触发onRefresh;另外还有一个,在FrameworkServlet中有一个onApplicationEvent方法,而这个方法又会被内部类ContextRefreshListener调用,这个类实现了ApplicationListener接口,表示会接收容器刷新事件。
以上就就是MVC HandlerMapping组件的初始化逻辑,其它组件实现逻辑相同,下面不再分析。

调用Controller

回到getHandler方法,其调用的是AbstractHandlerMapping类的方法:

	public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
		//根据请求的uri拿到对应的HandlerMethod对象
		Object handler = getHandlerInternal(request);
		if (handler == null) {
			handler = getDefaultHandler();
		}
		if (handler == null) {
			return null;
		}
		// Bean name or resolved handler?
		if (handler instanceof String) {
			String handlerName = (String) handler;
			handler = obtainApplicationContext().getBean(handlerName);
		}

		//获取HandlerMethod和过滤器链的包装类
		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());
		}

		//是否是跨域请求,就是查看request请求头中是否有Origin属性
		if (CorsUtils.isCorsRequest(request)) {
			//自定义的钩子方法获取跨域配置
			CorsConfiguration globalConfig = this.corsConfigurationSource.getCorsConfiguration(request);
			//注解获取跨域配置
			CorsConfiguration handlerConfig = getCorsConfiguration(handler, request);
			CorsConfiguration config = (globalConfig != null ? globalConfig.combine(handlerConfig) : handlerConfig);
			//这里设置了跨域的过滤器CorsInterceptor
			executionChain = getCorsHandlerExecutionChain(request, executionChain, config);
		}

		return executionChain;
	}

先看AbstractHandlerMethodMapping.getHandlerInternal

	protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception {
		//从request对象中获取uri,/common/query2
		String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);
		this.mappingRegistry.acquireReadLock();
		try {
			//根据uri从映射关系中找到对应的HandlerMethod对象
			HandlerMethod handlerMethod = lookupHandlerMethod(lookupPath, request);
			//把Controller类实例化
			return (handlerMethod != null ? handlerMethod.createWithResolvedBean() : null);
		}
		finally {
			this.mappingRegistry.releaseReadLock();
		}
	}

	protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception {
		List<Match> matches = new ArrayList<>();
		// 根据url拿到对应的RequestMappingInfo
		List<T> directPathMatches = this.mappingRegistry.getMappingsByUrl(lookupPath);
		if (directPathMatches != null) {
			addMatchingMappings(directPathMatches, matches, request);
		}
		if (matches.isEmpty()) {
			// No choice but to go through all mappings...
			addMatchingMappings(this.mappingRegistry.getMappings().keySet(), matches, request);
		}

		if (!matches.isEmpty()) {
			Comparator<Match> comparator = new MatchComparator(getMappingComparator(request));
			matches.sort(comparator);
			Match bestMatch = matches.get(0);
			if (matches.size() > 1) {
				if (logger.isTraceEnabled()) {
					logger.trace(matches.size() + " matching mappings: " + matches);
				}
				if (CorsUtils.isPreFlightRequest(request)) {
					return PREFLIGHT_AMBIGUOUS_MATCH;
				}
				Match secondBestMatch = matches.get(1);
				//如果两个RequestMappinginfo什么都相同,报错
				if (comparator.compare(bestMatch, secondBestMatch) == 0) {
					Method m1 = bestMatch.handlerMethod.getMethod();
					Method m2 = secondBestMatch.handlerMethod.getMethod();
					String uri = request.getRequestURI();
					throw new IllegalStateException(
							"Ambiguous handler methods mapped for '" + uri + "': {" + m1 + ", " + m2 + "}");
				}
			}
			request.setAttribute(BEST_MATCHING_HANDLER_ATTRIBUTE, bestMatch.handlerMethod);
			handleMatch(bestMatch.mapping, lookupPath, request);
			return bestMatch.handlerMethod;
		}
		else {
			return handleNoMatch(this.mappingRegistry.getMappings().keySet(), lookupPath, request);
		}
	}

	private void addMatchingMappings(Collection<T> mappings, List<Match> matches, HttpServletRequest request) {
		for (T mapping : mappings) {
			// 拿到匹配的RequestMappingInfo对象,有可能url相同,@RequestMapping的属性(请求方式、参数等)匹配不上
			T match = getMatchingMapping(mapping, request);
			if (match != null) {
				//RequestMappingInfo对象和HandlerMethod对象封装到Match对象中,其实就是注解属性和Method对象的映射
				matches.add(new Match(match, this.mappingRegistry.getMappings().get(mapping)));
			}
		}
	}

这里逻辑很简单,就是通过请求url从urlLookup中拿到对应的RequestMappingInfo(每一个 @RequestMapping对应一个RequestMappingInfo对象)对象,再根据RequestMappingInfo对象从mappingLookup拿到对应的HandlerMethod并返回。
但这里你可能会比较好奇urlLookupmappingLookup从哪里来的,仔细观察你会发现当前这个类实现了一个接口InitializingBean,实现了这个接口的类会在该类的Bean实例化完成后调用afterPropertiesSet方法,上面的映射关系就是在这个方法中做的。实际上这个方法不止完成了上面两个映射关系,还有下面两个:

  • corsLookup:handlerMethod -> corsConfig
  • registry:RequestMappingInfo -> MappingRegistration(包含url、handlerMethod、RequestMappingInfo、name等信息)

这里就不展开分析了,奉上一张时序图,读者可根据下面的时序图自行分析:
在这里插入图片描述
拿到HandlerMethod对象后,又会通过getHandlerExecutionChain方法去获取到所有的HandlerInterceptor拦截器对象,并连同HandlerMethod对象一起封装为HandlerExecutionChain。之后是获取跨域配置,这里不详细分析。
拿到HandlerExecutionChain对象后返回到doDispatch方法,又调用了getHandlerAdapter
方法拿到HandlerAdapter

	protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
		//根据handlerMethod对象,找到合适的HandlerAdapter对象,这里用到了策略模式
		if (this.handlerAdapters != null) {
			for (HandlerAdapter adapter : this.handlerAdapters) {
				if (adapter.supports(handler)) {
					return adapter;
				}
			}
		}
	}

这里的handlerAdapters变量值从哪里来?相信不用我再分析,主要看这里的设计思想,典型的策略模式
之后调用完前置过滤器后,才是真正调用我们controller方法的逻辑,通过HandlerAdapter.handle去调用,最终会调用到ServletInvocableHandlerMethod.invokeAndHandle

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

		//具体调用逻辑,重点看
		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 {
			//返回值处理
			this.returnValueHandlers.handleReturnValue(
					returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
		}
		catch (Exception ex) {
			if (logger.isTraceEnabled()) {
				logger.trace(formatErrorForReturnValue(returnValue), ex);
			}
			throw ex;
		}
	}

这个方法里面主要看invokeForRequesthandleReturnValue的调用,前者是完成参数绑定并调用controller,后者则是对返回值进行处理并封装到ModelAndViewContainer中。先来看invokeForRequest

	public Object invokeForRequest(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
			Object... providedArgs) throws Exception {

		//获取参数数组
		Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);
		if (logger.isTraceEnabled()) {
			logger.trace("Arguments: " + Arrays.toString(args));
		}
		return doInvoke(args);
	}

doInvoke就是完成反射调用,主要还是看参数绑定的实现逻辑,在getMethodArgumentValues方法中:

	protected Object[] getMethodArgumentValues(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
			Object... providedArgs) throws Exception {

		if (ObjectUtils.isEmpty(getMethodParameters())) {
			return EMPTY_ARGS;
		}
		//入参的包装类,里面包装了参数类型,参数名称,参数注解等等信息
		MethodParameter[] parameters = getMethodParameters();
		Object[] args = new Object[parameters.length];
		for (int i = 0; i < parameters.length; i++) {
			MethodParameter parameter = parameters[i];
			//设置参数名称解析器
			parameter.initParameterNameDiscovery(this.parameterNameDiscoverer);
			args[i] = findProvidedArgument(parameter, providedArgs);
			if (args[i] != null) {
				continue;
			}
			//典型的策略模式,根据parameter能否找到对应参数的处理类,能找到就返回true
			if (!this.resolvers.supportsParameter(parameter)) {
				throw new IllegalStateException(formatArgumentError(parameter, "No suitable resolver"));
			}
			try {
				//具体参数值解析过程,重点看看
				args[i] = this.resolvers.resolveArgument(parameter, mavContainer, request, this.dataBinderFactory);
			}
			catch (Exception ex) {
				// Leave stack trace for later, exception may actually be resolved and handled..
				if (logger.isDebugEnabled()) {
					String error = ex.getMessage();
					if (error != null && !error.contains(parameter.getExecutable().toGenericString())) {
						logger.debug(formatArgumentError(parameter, error));
					}
				}
				throw ex;
			}
		}
		return args;
	}

参数、返回值解析

因为参数类型非常多,同时还会伴随各种注解,如:@RequestBody、@RequestParam、@PathVariable等,所以参数解析的工作是非常繁杂的,同时还要考虑到扩展性,所以SpringMVC依然采用了策略模式来完成对各种参数类型的解析绑定,其顶层接口就是HandlerMethodArgumentResolver,而默认SpringMVC提供的解析方式就高达20多种:
在这里插入图片描述
上面是类图,读者可根据自己熟悉的参数类型找到对应的类进行分析,最核心的还是要掌握这里的设计思想。
接着方法调用完成后就是对返回值的处理,同样的,返回值类型也是非常多,也可以使用各种注解标注,所以也是使用策略模式实现,其顶层接口是HandlerMethodReturnValueHandler,实现类如下:
在这里插入图片描述
调用完成之后就是执行后续操作了:执行中置过滤器、处理全局异常、视图渲染以及执行后置过滤器,这些与主流程没有太大关系,本篇不展开分析了,最后是MVC的执行时序图:
在这里插入图片描述

总结

本篇是Spring核心原理系列的最后一篇,前前后后花了一个月时间,终于从宏观上大致上理解了Spring的实现原理和运行机制,明白了之前项目中一些坑是如何产生的,最主要的是学到设计模式的运用以及如何利用Spring的一些常用的扩展点进行自定义扩展。但对于Spring这个庞大的体系来说,还有很多是要去理解学习的,尤其是设计思想,只有长期琢磨才能深刻的理解掌握。在我之前的文章中包括本篇还有很多没分析到的细节,在后面我会不定期分享出来。

posted @ 2020-06-16 23:27  夜勿语  阅读(223)  评论(0编辑  收藏