SpringMVC源码情操陶冶-DispatcherServlet类简析（一）

阅读源码有利于陶冶情操，此文承接前文SpringMVC源码情操陶冶-DispatcherServlet父类简析

注意：springmvc初始化其他内容，其对应的配置文件已被加载至beanFactory中

DispatcherServlet#静态方法

DispatcherServlet静态块读取DispatcherServlet.properties，其中包含默认的策略实现

static {

		// Load default strategy implementations from properties file.

		// This is currently strictly internal and not meant to be customized

		// by application developers.

		try {

			ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, DispatcherServlet.class);

			defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);

		}

		catch (IOException ex) {

			throw new IllegalStateException("Could not load 'DispatcherServlet.properties': " + ex.getMessage());

		}

	}

简单看下DispatcherServlet.properties文件，具体内容如下

# Default implementation classes for DispatcherServlet's strategy interfaces.

# Used as fallback when no matching beans are found in the DispatcherServlet context.

# Not meant to be customized by application developers.

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

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

#url映射

org.springframework.web.servlet.HandlerMapping=org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping,\

	org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping

#适配器

org.springframework.web.servlet.HandlerAdapter=org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter,\

	org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter,\

	org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter

#异常解析

org.springframework.web.servlet.HandlerExceptionResolver=org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerExceptionResolver,\

	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

#视图解析

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

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

DispatcherServlet#onRefresh

复写父类FrameworkServlet的onRefresh()方法，springmvc以此来完善相应的初始化操作，代码如下

	//复写

	@Override

	protected void onRefresh(ApplicationContext context) {

		initStrategies(context);

	}

直接看DispatcherServlet#initStrategies()初始化springmvc的策略对象，代码如下

protected void initStrategies(ApplicationContext context) {

		initMultipartResolver(context);

		initLocaleResolver(context);

		initThemeResolver(context);

		initHandlerMappings(context);

		initHandlerAdapters(context);

		initHandlerExceptionResolvers(context);

		initRequestToViewNameTranslator(context);

		initViewResolvers(context);

		initFlashMapManager(context);

	}

以上述程序的执行顺序，逐个分析

DispatcherServlet#initMultipartResolver(ApplicationContext context)

根据官方注释，此会去加载beanFactory的multipartResolverbean对象，适用于处理文件上传的操作，简单代码如下

private void initMultipartResolver(ApplicationContext context) {

		try {

			this.multipartResolver = context.getBean(MULTIPART_RESOLVER_BEAN_NAME, MultipartResolver.class);

			if (logger.isDebugEnabled()) {

				logger.debug("Using MultipartResolver [" + this.multipartResolver + "]");

			}

		}

		catch (NoSuchBeanDefinitionException ex) {

			// Default is no multipart resolver.默认是没有对应的文件上传处理类的

			this.multipartResolver = null;

			if (logger.isDebugEnabled()) {

				logger.debug("Unable to locate MultipartResolver with name '" + MULTIPART_RESOLVER_BEAN_NAME +

						"': no multipart request handling provided");

			}

		}

	}

DispatcherServlet#initLocaleResolver(ApplicationContext context)

本地校对解析，官方解释为获取id="localeResolver"的bean对象，如果没有则使用默认的org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver类创建bean对象

private void initLocaleResolver(ApplicationContext context) {

		try {

			this.localeResolver = context.getBean(LOCALE_RESOLVER_BEAN_NAME, LocaleResolver.class);

			if (logger.isDebugEnabled()) {

				logger.debug("Using LocaleResolver [" + this.localeResolver + "]");

			}

		}

		catch (NoSuchBeanDefinitionException ex) {

			// We need to use the default.

			this.localeResolver = getDefaultStrategy(context, LocaleResolver.class);

			if (logger.isDebugEnabled()) {

				logger.debug("Unable to locate LocaleResolver with name '" + LOCALE_RESOLVER_BEAN_NAME +

						"': using default [" + this.localeResolver + "]");

			}

		}

	}

Note：这里我们简单看下DispatcherServlet#getDefaultStrategy()的内部方法createDefaultStrategy()创建spring bean对象

protected Object createDefaultStrategy(ApplicationContext context, Class<?> clazz) {

//可通过ApplicationContext.getAutowireCapableBeanFactory()方法来额外的创建外部class为bean对象

return context.getAutowireCapableBeanFactory().createBean(clazz);

}

DispatcherServlet#initThemeResolver(ApplicationContext context)

同DispatcherServlet#initLocaleResolver(ApplicationContext context)，找寻id="themeResolver"的bean对象，没有则默认使用org.springframework.web.servlet.theme.FixedThemeResolver作为bean对象

DispatcherServlet#initHandlerMappings(ApplicationContext context)

初始化对资源访问的映射处理类，代码如下

private void initHandlerMappings(ApplicationContext context) {

		this.handlerMappings = null;

		/***默认为true，表示从beanFactory和其父类获取所有的HandlerMapping

		** beans

		**<init-param>

		* <param-name>detectAllHandlerMappings</param-name>

		* <param-value>true/false</param-value>

		*/

		if (this.detectAllHandlerMappings) {

			//从祖先类到子类都去找寻相应的资源

			Map<String, HandlerMapping> matchingBeans =

				BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);

			if (!matchingBeans.isEmpty()) {

				this.handlerMappings = new ArrayList<HandlerMapping>(matchingBeans.values());

				// We keep HandlerMappings in sorted order.

				//根据优先级排序

				OrderComparator.sort(this.handlerMappings);

			}

		}

		else {

			try {

				//否则获取本springmvc的上下文中的单个`id="handlerMapping"`的HandlerMapping bean

				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.

			}

		}

		//如果detectAllHandlerMappings=false且springmvc不包含相应的`handlerMapping`bean 则取默认的HandlerMappings

		if (this.handlerMappings == null) {

			this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);

			if (logger.isDebugEnabled()) {

				logger.debug("No HandlerMappings found in servlet '" + getServletName() + "': using default");

			}

		}

	}

默认的HandlerMappings为org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping和

org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping，从字面上可知前者是根据beanName直接映射请求，后者是注解方式的映射请求

DispatcherServlet#initHandlerAdapters(ApplicationContext context)

此处类似DispatcherServlet#initHandlerMapping()：

detectAllHandlerAdapters默认为true，也可通过web.xml修改值，表示找寻所有满足HandlerAdapter.class的beans；若为false，则寻找springmvc本身上下文环境（springmvc配置文件）的id="handlerAdapter"的单个bean对象。所以不管如何，springmvc若指定了handlerAdapterbean，其总是会被加载

默认的策略对象为SimpleControllerHandlerAdapter-简单的Controller请求处理

DispatcherServlet#initHandlerExceptionResolvers(ApplicationContext context)

此处类似DispatcherServlet#initHandlerMapping()：

detectAllHandlerExceptionResolvers默认为true，也可通过web.xml修改值，表示找寻所有满足HandlerExceptionResolver.class的beans；若为false，则寻找springmvc本身上下文环境（springmvc配置文件）的id="handlerExceptionResolver"的单个bean对象。所以不管如何，springmvc若指定了handlerExceptionResolverbean，其总是会被加载

默认的策略对象为SimpleControllerHandlerAdapter-简单的Controller请求处理

DispatcherServlet#initRequestToViewNameTranslator(ApplicationContext context)

此处同DispatcherServlet#initLocaleResolver()方法

首先找寻springmvc上下文中的id="viewNameTranslator"的bean，类型为RequestToViewNameTranslator.class

不然则采用默认的策略对象org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator-对请求的URI直接映射到view对象

DispatcherServlet#initViewResolvers(ApplicationContext context)

此处类似DispatcherServlet#initViewResolvers()：

detectAllViewResolvers默认为true，也可通过web.xml修改值，表示找寻所有满足ViewResolver.class的beans；若为false，则寻找springmvc本身上下文环境（springmvc配置文件）的id="viewResolver"的单个bean对象。所以不管如何，springmvc若指定了viewResolverbean，其总是会被加载

默认的策略对象为InternalResourceViewResolver-默认解析为jsp视图

DispatcherServlet#initFlashMapManager(ApplicationContext context)

此处同DispatcherServlet#initLocaleResolver()方法

首先找寻springmvc上下文中的id="flashMapManager"的bean，类型为FlashMapManager.class

不然则采用默认的策略对象org.springframework.web.servlet.support.SessionFlashMapManager-保存并检索FlashMap属性

小结

本文只介绍springmvc额外的初始化操作，包括文件上传处理类、请求映射处理类/适配器、异常处理类、视图解析类等等