Spring之SpringMVC(源码)初始化DispatcherServlet策略配置

1.从上一篇文章中可以SpringMVC初始化的过程中完成的其中一件事就是DispatcherServlet的相关策略的配置，如下所示

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

　　下面分别看下，每个策略配置的具体实现

2.文件类型解析器

	private void initMultipartResolver(ApplicationContext context) {
		try {
　　　　　　　　　　　　　　//public static final String MULTIPART_RESOLVER_BEAN_NAME = "multipartResolver"
			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.
			this.multipartResolver = null;
			if (logger.isDebugEnabled()) {
				logger.debug("Unable to locate MultipartResolver with name '" + MULTIPART_RESOLVER_BEAN_NAME +
						"': no multipart request handling provided");
			}
		}
	}

　　通过初始化这个类来处理文件解析，但是也可以发现如果没有提供的话，就会给出一个空的的解析器。

3. LocaleResolver解析器

	private void initLocaleResolver(ApplicationContext context) {
		try {// public static final String LOCALE_RESOLVER_BEAN_NAME = "localeResolver";
			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 + "]");
			}
		}
	}

　　

为了让web应用程序支持国际化，必须识别每个用户的首选区域，并根据这个区域显示内容。LocaleResolver解析器主要解决国际化的问题。如果配置了那么就使用所配置的解析器，如果没有配置的话，那么就是用默认提供的AcceptHeaderLocaleResolver。

4.ThemeResolver

主题样式解析器，

	private void initThemeResolver(ApplicationContext context) {
		try {// public static final String THEME_RESOLVER_BEAN_NAME = "themeResolver";
			this.themeResolver = context.getBean(THEME_RESOLVER_BEAN_NAME, ThemeResolver.class);
			if (logger.isDebugEnabled()) {
				logger.debug("Using ThemeResolver [" + this.themeResolver + "]");
			}
		}
		catch (NoSuchBeanDefinitionException ex) {
			// We need to use the default.
			this.themeResolver = getDefaultStrategy(context, ThemeResolver.class);
			if (logger.isDebugEnabled()) {
				logger.debug(
						"Unable to locate ThemeResolver with name '" + THEME_RESOLVER_BEAN_NAME + "': using default [" +
								this.themeResolver + "]");
			}
		}
	}

　　如果提供了提供了相应的主题解析器，那么就是用，否则的话就是提供一个默认的FixedThemeResolver来作为主题解析器，

5.处理器映射解析器

	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<HandlerMapping>(matchingBeans.values());
				// We keep HandlerMappings in sorted order.
				OrderComparator.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.
			}
		}

　　请求到处理器的映射，如果映射成功返回一个HandlerExecutionChain对象（包含一个Handler处理器（页面控制器）对象、多个HandlerInterceptor拦截器）对象；BeanNameUrlHandlerMapping将URL与Bean名字映射，映射成功的Bean就是此处的处理器；通过这个类来初始化HandlerMappings，主要完成请求和处理器之间的映射关系。如果没有提供的话那么就会使用默认的BeanNameUrlHandlerMapping来进项相关的处理。我们来看下大致的处理过程。首先会获取所有的处理映射，然后对这些请求映射进项排序；如果请求映射集合为空，那么就会找到系统中的HandlerMapping，并且进行单例操作处理。如果这个HandlerMapping对象为空，就会使用默认的HandlerMapping，也就是BeanNameUrlHandlerMapping。

6.handlerAdapter解析器

private void initHandlerAdapters(ApplicationContext context) {
		this.handlerAdapters = null;

		if (this.detectAllHandlerAdapters) {
			// Find all HandlerAdapters in the ApplicationContext, including ancestor contexts.
			Map<String, HandlerAdapter> matchingBeans =
					BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerAdapter.class, true, false);
			if (!matchingBeans.isEmpty()) {
				this.handlerAdapters = new ArrayList<HandlerAdapter>(matchingBeans.values());
				// We keep HandlerAdapters in sorted order.
				OrderComparator.sort(this.handlerAdapters);
			}
		}
		else {
			try {
				HandlerAdapter ha = context.getBean(HANDLER_ADAPTER_BEAN_NAME, HandlerAdapter.class);
				this.handlerAdapters = Collections.singletonList(ha);
			}
			catch (NoSuchBeanDefinitionException ex) {
				// Ignore, we'll add a default HandlerAdapter later.
			}
		}

		// Ensure we have at least some HandlerAdapters, by registering
		// default HandlerAdapters if no other adapters are found.
		if (this.handlerAdapters == null) {
			this.handlerAdapters = getDefaultStrategies(context, HandlerAdapter.class);
			if (logger.isDebugEnabled()) {
				logger.debug("No HandlerAdapters found in servlet '" + getServletName() + "': using default");
			}
		}
	}

　　HandlerAdapter将会把处理器包装为适配器，从而支持多种类型的处理器，即适配器设计模式的应用，从而很容易支持很多类型的处理器。也就是说按照特定规则（HandlerAdapter要求的规则）去执行Handler。它会首先获取ApplicationContext中所有的处理适配器，如果获取集合不为空，需要进行排序处理。没有找到，则会查找系统中的handlerAdapter,然后进行单例化处理。如果查找的系统handlerAdapter为空，则使用默认的适配器，也即是SimpleControllerHandlerAdapter，它将对实现了Controller接口的Bean进行适配，并且掉处理器的handleRequest方法进行功能处理。

7.HandlerExceptionResolver

	private void initHandlerExceptionResolvers(ApplicationContext context) {
		this.handlerExceptionResolvers = null;

		if (this.detectAllHandlerExceptionResolvers) {
			// Find all HandlerExceptionResolvers in the ApplicationContext, including ancestor contexts.
			Map<String, HandlerExceptionResolver> matchingBeans = BeanFactoryUtils
					.beansOfTypeIncludingAncestors(context, HandlerExceptionResolver.class, true, false);
			if (!matchingBeans.isEmpty()) {
				this.handlerExceptionResolvers = new ArrayList<HandlerExceptionResolver>(matchingBeans.values());
				// We keep HandlerExceptionResolvers in sorted order.
				OrderComparator.sort(this.handlerExceptionResolvers);
			}
		}
		else {
			try {
				HandlerExceptionResolver her =
						context.getBean(HANDLER_EXCEPTION_RESOLVER_BEAN_NAME, HandlerExceptionResolver.class);
				this.handlerExceptionResolvers = Collections.singletonList(her);
			}
			catch (NoSuchBeanDefinitionException ex) {
				// Ignore, no HandlerExceptionResolver is fine too.
			}
		}

		// Ensure we have at least some HandlerExceptionResolvers, by registering
		// default HandlerExceptionResolvers if no other resolvers are found.
		if (this.handlerExceptionResolvers == null) {
			this.handlerExceptionResolvers = getDefaultStrategies(context, HandlerExceptionResolver.class);
			if (logger.isDebugEnabled()) {
				logger.debug("No HandlerExceptionResolvers found in servlet '" + getServletName() + "': using default");
			}
		}
	}

　　通过这个方法来初始化HandlerExceptionResolver，如果没有配置，系统默认不会提供处理器异常解析器，会给一个空的来作为默认。它首先会查找ApplicationContext中所有的配置的处理器异常解析器，包括它的父容器的范围的，如果找到了会进行有序处理操作（ Map<String, HandlerExceptionResolver>）；如果找不到具体的映射配置，那么就会获取ApplicationContext中的HandlerExceptionResolver并且进行单例化处理。如果获取的这个解析器为空，那么就会使用默认的，也就是空的解析器处理。

8.RequestToViewNameTranslator

	private void initRequestToViewNameTranslator(ApplicationContext context) {
		try {
			this.viewNameTranslator =
					context.getBean(REQUEST_TO_VIEW_NAME_TRANSLATOR_BEAN_NAME, RequestToViewNameTranslator.class);
			if (logger.isDebugEnabled()) {
				logger.debug("Using RequestToViewNameTranslator [" + this.viewNameTranslator + "]");
			}
		}
		catch (NoSuchBeanDefinitionException ex) {
			// We need to use the default.
			this.viewNameTranslator = getDefaultStrategy(context, RequestToViewNameTranslator.class);
			if (logger.isDebugEnabled()) {
				logger.debug("Unable to locate RequestToViewNameTranslator with name '" +
						REQUEST_TO_VIEW_NAME_TRANSLATOR_BEAN_NAME + "': using default [" + this.viewNameTranslator +
						"]");
			}
		}
	}

通过提供的 Servlet实例来初始化RequestToViewNameTranslator，如果没有提供的话，就会使用系统默认的DefaultRequestToViewNameTranslator。

9.视图解析器

private void initViewResolvers(ApplicationContext context) {
		this.viewResolvers = null;

		if (this.detectAllViewResolvers) {
			// Find all ViewResolvers in the ApplicationContext, including ancestor contexts.
			Map<String, ViewResolver> matchingBeans =
					BeanFactoryUtils.beansOfTypeIncludingAncestors(context, ViewResolver.class, true, false);
			if (!matchingBeans.isEmpty()) {
				this.viewResolvers = new ArrayList<ViewResolver>(matchingBeans.values());
				// We keep ViewResolvers in sorted order.
				OrderComparator.sort(this.viewResolvers);
			}
		}
		else {
			try {
				ViewResolver vr = context.getBean(VIEW_RESOLVER_BEAN_NAME, ViewResolver.class);
				this.viewResolvers = Collections.singletonList(vr);
			}
			catch (NoSuchBeanDefinitionException ex) {
				// Ignore, we'll add a default ViewResolver later.
			}
		}

		// Ensure we have at least one ViewResolver, by registering
		// a default ViewResolver if no other resolvers are found.
		if (this.viewResolvers == null) {
			this.viewResolvers = getDefaultStrategies(context, ViewResolver.class);
			if (logger.isDebugEnabled()) {
				logger.debug("No ViewResolvers found in servlet '" + getServletName() + "': using default");
			}
		}
	}

通过这个来进行视图解析器的初始化工作，如果没有提供的话那么就会使用InternalResourceViewResolver来进行处理，是不是对JSP页面处理的时候经常看到这个配置。

10.FlashMapManager

	private void initFlashMapManager(ApplicationContext context) {
		try {
			this.flashMapManager =
					context.getBean(FLASH_MAP_MANAGER_BEAN_NAME, FlashMapManager.class);
			if (logger.isDebugEnabled()) {
				logger.debug("Using FlashMapManager [" + this.flashMapManager + "]");
			}
		}
		catch (NoSuchBeanDefinitionException ex) {
			// We need to use the default.
			this.flashMapManager = getDefaultStrategy(context, FlashMapManager.class);
			if (logger.isDebugEnabled()) {
				logger.debug("Unable to locate FlashMapManager with name '" +
						FLASH_MAP_MANAGER_BEAN_NAME + "': using default [" + this.flashMapManager + "]");
			}
		}
	}

　　从方法中的注释可知，如果用户没有提供它的配置，那么就是使用spring提供的org.springframework.web.servlet.support.DefaultFlashMapManager来作为默认的处理。

11.常量配置

11.1关于上面的初始化的配置常量

	/** Well-known name for the MultipartResolver object in the bean factory for this namespace. */
	public static final String MULTIPART_RESOLVER_BEAN_NAME = "multipartResolver";

	/** Well-known name for the LocaleResolver object in the bean factory for this namespace. */
	public static final String LOCALE_RESOLVER_BEAN_NAME = "localeResolver";

	/** Well-known name for the ThemeResolver object in the bean factory for this namespace. */
	public static final String THEME_RESOLVER_BEAN_NAME = "themeResolver";

	/**
	 * Well-known name for the HandlerMapping object in the bean factory for this namespace.
	 * Only used when "detectAllHandlerMappings" is turned off.
	 * @see #setDetectAllHandlerMappings
	 */
	public static final String HANDLER_MAPPING_BEAN_NAME = "handlerMapping";

	/**
	 * Well-known name for the HandlerAdapter object in the bean factory for this namespace.
	 * Only used when "detectAllHandlerAdapters" is turned off.
	 * @see #setDetectAllHandlerAdapters
	 */
	public static final String HANDLER_ADAPTER_BEAN_NAME = "handlerAdapter";

	/**
	 * Well-known name for the HandlerExceptionResolver object in the bean factory for this namespace.
	 * Only used when "detectAllHandlerExceptionResolvers" is turned off.
	 * @see #setDetectAllHandlerExceptionResolvers
	 */
	public static final String HANDLER_EXCEPTION_RESOLVER_BEAN_NAME = "handlerExceptionResolver";

	/**
	 * Well-known name for the RequestToViewNameTranslator object in the bean factory for this namespace.
	 */
	public static final String REQUEST_TO_VIEW_NAME_TRANSLATOR_BEAN_NAME = "viewNameTranslator";

	/**
	 * Well-known name for the ViewResolver object in the bean factory for this namespace.
	 * Only used when "detectAllViewResolvers" is turned off.
	 * @see #setDetectAllViewResolvers
	 */
	public static final String VIEW_RESOLVER_BEAN_NAME = "viewResolver";

	/**
	 * Well-known name for the FlashMapManager object in the bean factory for this namespace.
	 */
	public static final String FLASH_MAP_MANAGER_BEAN_NAME = "flashMapManager";

	/**
	 * Request attribute to hold the current web application context.
	 * Otherwise only the global web app context is obtainable by tags etc.
	 * @see org.springframework.web.servlet.support.RequestContextUtils#getWebApplicationContext
	 */
	public static final String WEB_APPLICATION_CONTEXT_ATTRIBUTE = DispatcherServlet.class.getName() + ".CONTEXT";

	/**
	 * Request attribute to hold the current LocaleResolver, retrievable by views.
	 * @see org.springframework.web.servlet.support.RequestContextUtils#getLocaleResolver
	 */
	public static final String LOCALE_RESOLVER_ATTRIBUTE = DispatcherServlet.class.getName() + ".LOCALE_RESOLVER";

	/**
	 * Request attribute to hold the current ThemeResolver, retrievable by views.
	 * @see org.springframework.web.servlet.support.RequestContextUtils#getThemeResolver
	 */
	public static final String THEME_RESOLVER_ATTRIBUTE = DispatcherServlet.class.getName() + ".THEME_RESOLVER";

	/**
	 * Request attribute to hold the current ThemeSource, retrievable by views.
	 * @see org.springframework.web.servlet.support.RequestContextUtils#getThemeSource
	 */
	public static final String THEME_SOURCE_ATTRIBUTE = DispatcherServlet.class.getName() + ".THEME_SOURCE";

	/**
	 * Name of request attribute that holds a read-only {@code Map<String,?>}
	 * with "input" flash attributes saved by a previous request, if any.
	 * @see org.springframework.web.servlet.support.RequestContextUtils#getInputFlashMap(HttpServletRequest)
	 */
	public static final String INPUT_FLASH_MAP_ATTRIBUTE = DispatcherServlet.class.getName() + ".INPUT_FLASH_MAP";

	/**
	 * Name of request attribute that holds the "output" {@link FlashMap} with
	 * attributes to save for a subsequent request.
	 * @see org.springframework.web.servlet.support.RequestContextUtils#getOutputFlashMap(HttpServletRequest)
	 */
	public static final String OUTPUT_FLASH_MAP_ATTRIBUTE = DispatcherServlet.class.getName() + ".OUTPUT_FLASH_MAP";

	/**
	 * Name of request attribute that holds the {@link FlashMapManager}.
	 * @see org.springframework.web.servlet.support.RequestContextUtils#getFlashMapManager(HttpServletRequest)
	 */
	public static final String FLASH_MAP_MANAGER_ATTRIBUTE = DispatcherServlet.class.getName() + ".FLASH_MAP_MANAGER";

	/** Log category to use when no mapped handler is found for a request. */
	public static final String PAGE_NOT_FOUND_LOG_CATEGORY = "org.springframework.web.servlet.PageNotFound";

	/**
	 * Name of the class path resource (relative to the DispatcherServlet class)
	 * that defines DispatcherServlet's default strategy names.
	 */
	private static final String DEFAULT_STRATEGIES_PATH = "DispatcherServlet.properties";

　　11.2Spring提供的默认配置文件DispatcherServlet.properties

# 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

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

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

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

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

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

　　有上面的SpringMVC默认的配置文件可知，相应的策略实现有系统默认的配置项。