Spring MVC之DispatcherServlet初始化

     使用Spring MVC 时，需要在web.xml中配置DispatchServlet,这个DispatchServlet可以看成一个控制器的具体实现。作为一个控制器所有的请求都要通过它来处理，进行转发、匹配、数据处理后并转由页面进行展示。因此DispatchServlet是Spring MVC的核心部分。    

      在完成ContextLoaderListener的初始化后，Web容器开始初始化DispatcherServlet,这个初始化的启动与在web.xml中对载入次序的定义有关。DispathcerServlet会建立自己的上下文来持有Spring MVC的Bean,在建立这个自己的IOC容器时，会从ServletContext中得到根上下文作为自己持有上下文的双亲上下文。有了这个根上下文再对自己持有的上下文进行初始化，最后将自己持有的上下文保存到ServletContext中。

 

     首先看看DispatcherSerlvet的继承关系：DispatcherServlet继承自FrameworkServlet,而FrameworkServet继承自HttpServletBean.HttpServletBean有继承了HttpServlet.

    DispatcherServlet动作大致可以分为两个部分：初始化部分由initServletBean()启动，通过initWebApplicationContext()方法调用DispatcherServlet的initStrategies方法。在这个方法里，DispatcherServlet对MVC的其他部分进行了初始化，比如handlerMapping,ViewResolver;另一个部分是对Http的请求进行响应，作为一个Servlet，web容器会调用Servlet的doGet()和doPost()方法，在经过FrameServlet的processRequest（）简单处理后，会调用DispatcherServlet的doService（）方法，在这个方法中封装了doDispatch().

     在这里主要介绍初始化部分。

    作为Servlet, DispatcherServlet的启动过程和Servlet启动过程是相联系的。在Servlet的初始化过程中，Servlet的init方法被调用，已进行初始化。

HttppServletBean.init()->FrameworkServlet.initWebApplicationContext()->DispatcherServlet.onRefresh().

onRefresh 的源码是：

 

	/**
	 * This implementation calls {@link #initStrategies}.
	 */
	@Override
	protected void onRefresh(ApplicationContext context) {
		initStrategies(context);
	}

 而initStrategies(context)的源码如下：

 

 

 

	protected void initStrategies(ApplicationContext context) {
		//初始化多媒体解析器
		initMultipartResolver(context);
		//初始化位置解析器
		initLocaleResolver(context);
		//初始化主题解析器
		initThemeResolver(context);
		//初始化HandlerMappings
		initHandlerMappings(context);
		// 初始化HandlerAdapters
		initHandlerAdapters(context);
		//初始化异常解析器
		initHandlerExceptionResolvers(context);
		//初始化请求到视图名转换器
		initRequestToViewNameTranslator(context);
		//初始化视图解析器
		initViewResolvers(context);
		//初始化FlashMapManager
		initFlashMapManager(context);
	}

     通过initMultipartResover进行初始化多媒体解析器，如果在配置文件中没有配置id为multipartResolver的bean则没有提供多媒体处理器。

 

 

 

/**
	 * Initialize the MultipartResolver used by this class.
	 * <p>If no bean is defined with the given name in the BeanFactory for this namespace,
	 * no multipart handling is provided.
	 */
	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.
			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initLocaleResolver方法进行localeResolver的初始化，如果没有配置指定id为localeResolver的bean则使用AcceptHeaderLocaleResolver的位置解析器。

 * Initialize the LocaleResolver used by this class.
	 * <p>If no bean is defined with the given name in the BeanFactory for this namespace,
	 * we default to AcceptHeaderLocaleResolver.
	 */
	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 + "]");
			}
		}
	}

 initThemeResolver初始化主题解析器，如果没有配置指定id的为themeResolver的bean 则使用FixedThemeResolver主题解析器

	/**
	 * Initialize the ThemeResolver used by this class.
	 * <p>If no bean is defined with the given name in the BeanFactory for this namespace,
	 * we default to a FixedThemeResolver.
	 */
	private void initThemeResolver(ApplicationContext context) {
		try {
			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 + "]");
			}
		}
	}

 初始化HandlerMapping,这个handlerMapping的作用是为Http请求找到相应的控制器，从而利用这些控制器去完成http请求的数据处理工作。这些控制器和http的请求时对应的。DispatcherServlet中handlerMapping的初始化过程中的具体实现如下。在HandlerMapping的初始化过程中，把Bean配置文件中配置好的handlerMapping从IOC容器中取出。

	/**
	 * Initialize the HandlerMappings used by this class.
	 * <p>If no HandlerMapping beans are defined in the BeanFactory for this namespace,
	 * we default to BeanNameUrlHandlerMapping.
	 */
	private void initHandlerMappings(ApplicationContext context) {
		this.handlerMappings = null;
	
		if (this.detectAllHandlerMappings) {
			// 在应用上下文包括其祖先上下文中查找所有HandlerMappings
			Map<String, HandlerMapping> matchingBeans =
					BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
			//如果matchingBeans这个map是不为空，则创建一个新的ArrayList
			if (!matchingBeans.isEmpty()) {
				this.handlerMappings = new ArrayList<HandlerMapping>(matchingBeans.values());
				//并对其进行排序
				OrderComparator.sort(this.handlerMappings);
			}
		}
		else {
			try {
			    //从应用上下文中查找所有的HandlerMapping
				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.
			}
		}

		// Ensure we have at least one HandlerMapping, by registering
		// a default HandlerMapping if no other mappings are found.
		if (this.handlerMappings == null) {
			// 如果没有配置HandlerMapping 则使用默认的HandlerMapping 策略
			this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);
			if (logger.isDebugEnabled()) {
				logger.debug("No HandlerMappings found in servlet '" + getServletName() + "': using default");
			}
		}
	}

     进过上述的处理过程，handlerMapping已经初始化完成，handlerMapping中就已经获取了在BeanDefinition中配置的映射关系。

 

      通过initHandlerAdapters进行初始化HandlerAdapter,如果没有配置HandlerAdapter则使用SimpleControllerHandlerAdapter

 

/**
	 * Initialize the HandlerAdapters used by this class.
	 * <p>If no HandlerAdapter beans are defined in the BeanFactory for this namespace,
	 * we default to SimpleControllerHandlerAdapter.
	 */
	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");
			}
		}
	}

  初始化异常处理器，如果没有配置指定Id为handlerExceptionResolver的Bean，默认是没有异常处理器

	/**
	 * Initialize the HandlerExceptionResolver used by this class.
	 * <p>If no bean is defined with the given name in the BeanFactory for this namespace,
	 * we default to no exception resolver.
	 */
	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");
			}
		}
	}

 

初始化请求到视图名称的转换器，如果不配置则使用默认的转换器。

/**
	 * Initialize the RequestToViewNameTranslator used by this servlet instance.
	 * <p>If no implementation is configured then we default to DefaultRequestToViewNameTranslator.
	 */
	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 +
						"]");
			}
		}
	}

  初始化视图解析器，如果没有配置视图解析器则使用默认的InternalResourceViewResolver视图解析器

/**
	 * Initialize the ViewResolvers used by this class.
	 * <p>If no ViewResolver beans are defined in the BeanFactory for this
	 * namespace, we default to InternalResourceViewResolver.
	 */
	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");
			}
		}
	}

 获取默认设置，首先获取接口的名称，然后从DispatcherServlert.properties的配置文件中读取value,然后将其分割为字符串数组。

/**
	 * Create a List of default strategy objects for the given strategy interface.
	 * <p>The default implementation uses the "DispatcherServlet.properties" file (in the same
	 * package as the DispatcherServlet class) to determine the class names. It instantiates
	 * the strategy objects through the context's BeanFactory.
	 * @param context the current WebApplicationContext
	 * @param strategyInterface the strategy interface
	 * @return the List of corresponding strategy objects
	 */
	@SuppressWarnings("unchecked")
	protected <T> List<T> getDefaultStrategies(ApplicationContext context, Class<T> strategyInterface) {
		String key = strategyInterface.getName();
		String value = defaultStrategies.getProperty(key);
		if (value != null) {
			String[] classNames = StringUtils.commaDelimitedListToStringArray(value);
			List<T> strategies = new ArrayList<T>(classNames.length);
			for (String className : classNames) {
				try {
					Class<?> clazz = ClassUtils.forName(className, DispatcherServlet.class.getClassLoader());
					Object strategy = createDefaultStrategy(context, clazz);
					strategies.add((T) strategy);
				}
				catch (ClassNotFoundException ex) {
					throw new BeanInitializationException(
							"Could not find DispatcherServlet's default strategy class [" + className +
									"] for interface [" + key + "]", ex);
				}
				catch (LinkageError err) {
					throw new BeanInitializationException(
							"Error loading DispatcherServlet's default strategy class [" + className +
									"] for interface [" + key + "]: problem with class file or dependent class", err);
				}
			}
			return strategies;
		}
		else {
			return new LinkedList<T>();
		}
	}

 

 

 

DispatcherSerlvet.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

 

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1 楼 java_Gary 2014-12-29  

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