Spring源代码分析之Spring MVC与Web环境

朱雀 2022-08-27 14:46 170阅读 0赞

1 IOC是一个独立的模块，它是与Web容器启动过程中集成在一起的。在Web容器的启动过程中，一方面处理Web容器的启动，另一方面通过设计特定的Web容器拦截器，将IOC环境加载到Web环境中，并将其初始化。

<pre class="html" name="code"><pre class="html" name="code"> <context-param>
 <param-name>contextConfigLocation</param-name>
 <param-value>/WEB-INF/applicationContext.xml</param-value>
 </context-param>
 <listener>
 <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
 </listener>
 <servlet>
 <servlet-name>dispatcher</servlet-name>
 <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
 <load-on-startup>2</load-on-startup>
 </servlet>
 <servlet-mapping>
 <servlet-name>dispatcher</servlet-name>
 <url-pattern>/</url-pattern>
 </servlet-mapping>

dispatcher起着分发请求的作用。

<context-param>用来指定Spring容器读取Bean定义的Xml路径

ContextLoaderListener在web容器启动过程中负责完成IOC容器的初始化。

Dispatcher和ContextLoaderListener提供了在Web容器中对Spring的接口，也就是说，这些接口与Web容器耦合式通过ServletContext来实现的。这个ServletContext为SpringIOC容器提供了一个宿主环境。

2 IOC容器启动的基本过程

![SouthEast][]

ServletContextListener提供了与servlet生命周期结合的回调；

ContextLoader负责加载IOC容器；

WebApplicationContext接口：

public interface WebApplicationContext extends ApplicationContext {
    
    	//用于保存ServletContext的根上下文

String ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE = WebApplicationContext.class.getName() + ".ROOT";
 
 	/**
 	 * Scope identifier for request scope: "request".
 	 * Supported in addition to the standard scopes "singleton" and "prototype".
 	 */
 	String SCOPE_REQUEST = "request";
 
 	/**
 	 * Scope identifier for session scope: "session".
 	 * Supported in addition to the standard scopes "singleton" and "prototype".
 	 */
 	String SCOPE_SESSION = "session";
 
 	/**
 	 * Scope identifier for global session scope: "globalSession".
 	 * Supported in addition to the standard scopes "singleton" and "prototype".
 	 */
 	String SCOPE_GLOBAL_SESSION = "globalSession";
 
 	/**
 	 * Scope identifier for the global web application scope: "application".
 	 * Supported in addition to the standard scopes "singleton" and "prototype".
 	 */
 	String SCOPE_APPLICATION = "application";
 
 	/**
 	 * Name of the ServletContext environment bean in the factory.
 	 * @see javax.servlet.ServletContext
 	 */
 	String SERVLET_CONTEXT_BEAN_NAME = "servletContext";
 
 	/**
 	 * Name of the ServletContext/PortletContext init-params environment bean in the factory.
 	 * Note: Possibly merged with ServletConfig/PortletConfig parameters.
 	 * ServletConfig parameters override ServletContext parameters of the same name.
 	 * @see javax.servlet.ServletContext#getInitParameterNames()
 	 * @see javax.servlet.ServletContext#getInitParameter(String)
 	 * @see javax.servlet.ServletConfig#getInitParameterNames()
 	 * @see javax.servlet.ServletConfig#getInitParameter(String)
 	 */
 	String CONTEXT_PARAMETERS_BEAN_NAME = "contextParameters";
 
 	/**
 	 * Name of the ServletContext/PortletContext attributes environment bean in the factory.
 	 * @see javax.servlet.ServletContext#getAttributeNames()
 	 * @see javax.servlet.ServletContext#getAttribute(String)
 	 */
 	String CONTEXT_ATTRIBUTES_BEAN_NAME = "contextAttributes";
 
 
 	//获得Web容器的ServletContext上下文

ServletContext getServletContext();
    
    }

XmlWebApplicationContext：

public class XmlWebApplicationContext extends AbstractRefreshableWebApplicationContext {
 
 	//默认加载BeanDefinition的路径
 	public static final String DEFAULT_CONFIG_LOCATION = "/WEB-INF/applicationContext.xml";
 
 	//默认的配置文件所在的目录
 	public static final String DEFAULT_CONFIG_LOCATION_PREFIX = "/WEB-INF/";
 
 	//默认的配置文件的后缀
 	public static final String DEFAULT_CONFIG_LOCATION_SUFFIX = ".xml";
 
 
 	//load the BeanDefition visa XmlBeanDefinitionReader
 	protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
 		// Create a new XmlBeanDefinitionReader for the given BeanFactory.
 		XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
 
 		// Configure the bean definition reader with this context's
 		// resource loading environment.
 
 		beanDefinitionReader.setEnvironment(getEnvironment());
 		beanDefinitionReader.setResourceLoader(this);
 		beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
 
 		// Allow a subclass to provide custom initialization of the reader,
 		// then proceed with actually loading the bean definitions.
 		//允许子类为reader配置好自定义的初始化过程，之后加载BeanDefition
 		initBeanDefinitionReader(beanDefinitionReader);
 		//这里使用定义好的XmlBeanDefition来加载BeanDefition
 		loadBeanDefinitions(beanDefinitionReader);
 	}
 
 	/**
 	 * Initialize the bean definition reader used for loading the bean
 	 * definitions of this context. Default implementation is empty.
 	 */
 	protected void initBeanDefinitionReader(XmlBeanDefinitionReader beanDefinitionReader) {
 	}
 
 	/**
 	 * Load the bean definitions with the given XmlBeanDefinitionReader.
 	 * The lifecycle of the bean factory is handled by the refreshBeanFactory method;
 	 * therefore this method is just supposed to load and/or register bean definitions.
 	 * Delegates to a ResourcePatternResolver for resolving location patterns
 	 * into Resource instances.
 	 * @throws java.io.IOException if the required XML document isn't found
 	 * @see #refreshBeanFactory
 	 * @see #getConfigLocations
 	 * @see #getResources
 	 * @see #getResourcePatternResolver
 	 */
 	protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws IOException {
 		String[] configLocations = getConfigLocations();
 		if (configLocations != null) {
 			for (String configLocation : configLocations) {
 				reader.loadBeanDefinitions(configLocation);
 			}
 		}
 	}
 
 	/**
 	 * The default location for the root context is "/WEB-INF/applicationContext.xml",
 	 * and "/WEB-INF/test-servlet.xml" for a context with the namespace "test-servlet"
 	 * (like for a DispatcherServlet instance with the servlet-name "test").
 	 */
 	@Override
 	protected String[] getDefaultConfigLocations() {
 		if (getNamespace() != null) {
 			return new String[] {DEFAULT_CONFIG_LOCATION_PREFIX + getNamespace() + DEFAULT_CONFIG_LOCATION_SUFFIX};
 		}
 		else {
 			return new String[] {DEFAULT_CONFIG_LOCATION};
 		}
 	}
 
 }

ContexLoaderListener加载IOC容器的过程：

首先从Servlet的事件中获得ServletContext，然后加载web.xml的各个相关属性，接着ContextLoader会加载WebApplicationContext，完成初始化和加载过程。这个根上下文会被绑定到ServletContext中去。可以通过WebApplicationContextUtils的静态方法来获得跟上下文。

WebApplicationContext getWebApplicationContext(ServletContext sc) ;

下面是具体的根上下文的载入过程。在ContextLoaderListener实现了ServletContextListener接口，这个的函数会结合Web容器的生命周期被调用。ContextLoaderListener是ServletContext的监听者。服务器启动的时候，服务器关闭的时候，ServletContext被创建的时候，ServletContext被销毁的时候。

/**
    	 * Initialize the root web application context.
    	 */
    	public void contextInitialized(ServletContextEvent event) {
    		this.contextLoader = createContextLoader();
    		if (this.contextLoader == null) {
    			this.contextLoader = this;
    		}
    		this.contextLoader.initWebApplicationContext(event.getServletContext());
    	}

由上面的源代码可以看出具体的初始化工作是由ContextLoader来完成的。

/**
    	 * Initialize Spring's web application context for the given servlet context,
    	 * using the application context provided at construction time, or creating a new one
    	 * @param servletContext current servlet context
    	 * @return the new WebApplicationContext
    	 * @see #ContextLoader(WebApplicationContext)
    	 * @see #CONTEXT_CLASS_PARAM
    	 * @see #CONFIG_LOCATION_PARAM
    	 */
    	public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {
    		//判断ServletContext中是否有根上下文
    		if (servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE) != null) {
    			throw new IllegalStateException(
    					"Cannot initialize context because there is already a root application context present - " +
    					"check whether you have multiple ContextLoader* definitions in your web.xml!");
    		}
    
    		Log logger = LogFactory.getLog(ContextLoader.class);
    		servletContext.log("Initializing Spring root WebApplicationContext");
    		if (logger.isInfoEnabled()) {
    			logger.info("Root WebApplicationContext: initialization started");
    		}
    		long startTime = System.currentTimeMillis();
    
    		try {
    			// Store context in local instance variable, to guarantee that
    			// it is available on ServletContext shutdown.
    			if (this.context == null) {
    				this.context = createWebApplicationContext(servletContext);
    			}
    			if (this.context instanceof ConfigurableWebApplicationContext) {
    				ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context;
    				if (!cwac.isActive()) {
    					// The context has not yet been refreshed -> provide services such as
    					// setting the parent context, setting the application context id, etc
    					if (cwac.getParent() == null) {
    						// The context instance was injected without an explicit parent ->
    						// determine parent for root web application context, if any.
    						ApplicationContext parent = loadParentContext(servletContext);
    						cwac.setParent(parent);
    					}
    					configureAndRefreshWebApplicationContext(cwac, servletContext);
    				}
    			}
    			servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);
    
    			ClassLoader ccl = Thread.currentThread().getContextClassLoader();
    			if (ccl == ContextLoader.class.getClassLoader()) {
    				currentContext = this.context;
    			}
    			else if (ccl != null) {
    				currentContextPerThread.put(ccl, this.context);
    			}
    
    			if (logger.isDebugEnabled()) {
    				logger.debug("Published root WebApplicationContext as ServletContext attribute with name [" +
    						WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE + "]");
    			}
    			if (logger.isInfoEnabled()) {
    				long elapsedTime = System.currentTimeMillis() - startTime;
    				logger.info("Root WebApplicationContext: initialization completed in " + elapsedTime + " ms");
    			}
    
    			return this.context;
    		}
    		catch (RuntimeException ex) {
    			logger.error("Context initialization failed", ex);
    			servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, ex);
    			throw ex;
    		}
    		catch (Error err) {
    			logger.error("Context initialization failed", err);
    			servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, err);
    			throw err;
    		}
    	}

创建根上下文：

protected WebApplicationContext createWebApplicationContext(ServletContext sc) {
 		Class<?> contextClass = determineContextClass(sc);
 		if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
 			throw new ApplicationContextException("Custom context class [" + contextClass.getName() +
 					"] is not of type [" + ConfigurableWebApplicationContext.class.getName() + "]");
 		}
 		return (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);

/**
 	 * Return the WebApplicationContext implementation class to use, either the
 	 * default XmlWebApplicationContext or a custom context class if specified.
 	 * @param servletContext current servlet context
 	 * @return the WebApplicationContext implementation class to use
 	 * @see #CONTEXT_CLASS_PARAM
 	 * @see org.springframework.web.context.support.XmlWebApplicationContext
 	 */
 	protected Class<?> determineContextClass(ServletContext servletContext) {
 		//这里读取servletContext的CONTEXT_CLASS_PARAM参数
 		String contextClassName = servletContext.getInitParameter(CONTEXT_CLASS_PARAM);
 		//如果servletContext配置了CONTEXT_CLASS，则用这个class
 		if (contextClassName != null) {
 			try {
 				return ClassUtils.forName(contextClassName, ClassUtils.getDefaultClassLoader());
 			}
 			catch (ClassNotFoundException ex) {
 				throw new ApplicationContextException(
 						"Failed to load custom context class [" + contextClassName + "]", ex);
 			}
 		}
 		else {//如果没有配置，那么使用默认配置的class
 			contextClassName = defaultStrategies.getProperty(WebApplicationContext.class.getName());
 			try {
 				return ClassUtils.forName(contextClassName, ContextLoader.class.getClassLoader());
 			}
 			catch (ClassNotFoundException ex) {
 				throw new ApplicationContextException(
 						"Failed to load default context class [" + contextClassName + "]", ex);
 			}
 		}
 	}

在web.xml中，我们除了要配置ContextLoaderListener，还要配置Dispatcher,它是一个前端控制器，负责对请求进行转发，匹配。

![SouthEast 1][]

Dispatcher的初始化和加载过程

/**
    	 * Map config parameters onto bean properties of this servlet, and
    	 * invoke subclass initialization.
    	 * @throws ServletException if bean properties are invalid (or required
    	 * properties are missing), or if subclass initialization fails.
    	 */
    	public final void init() throws ServletException {
    		if (logger.isDebugEnabled()) {
    			logger.debug("Initializing servlet '" + getServletName() + "'");
    		}
    
    		// Set bean properties from init parameters.
    		//获取servlet的初始化参数，对Bean属性进行配置
    		try {
    			PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
    			BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
    			ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
    			bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
    			initBeanWrapper(bw);
    			bw.setPropertyValues(pvs, true);
    		}
    		catch (BeansException ex) {
    			logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);
    			throw ex;
    		}
    
    		// Let subclasses do whatever initialization they like.
    		//调用子类进行初始化
    		initServletBean();
    
    		if (logger.isDebugEnabled()) {
    			logger.debug("Servlet '" + getServletName() + "' configured successfully");
    		}
    	}

initServletBean方法在FrameworkServlet中完成

/**
    	 * Overridden method of {@link HttpServletBean}, invoked after any bean properties
    	 * have been set. Creates this servlet's WebApplicationContext.
    	 */
    	@Override
    	protected final void initServletBean() throws ServletException {
    		getServletContext().log("Initializing Spring FrameworkServlet '" + getServletName() + "'");
    		if (this.logger.isInfoEnabled()) {
    			this.logger.info("FrameworkServlet '" + getServletName() + "': initialization started");
    		}
    		long startTime = System.currentTimeMillis();
    
    		try {
    			//这里初始化上下文
    			this.webApplicationContext = initWebApplicationContext();
    			initFrameworkServlet();
    		}
    		catch (ServletException ex) {
    			this.logger.error("Context initialization failed", ex);
    			throw ex;
    		}
    		catch (RuntimeException ex) {
    			this.logger.error("Context initialization failed", ex);
    			throw ex;
    		}
    
    		if (this.logger.isInfoEnabled()) {
    			long elapsedTime = System.currentTimeMillis() - startTime;
    			this.logger.info("FrameworkServlet '" + getServletName() + "': initialization completed in " +
    					elapsedTime + " ms");
    		}
    	}

初始化上下文

/**
 	 * Initialize and publish the WebApplicationContext for this servlet.
 	 * Delegates to {@link #createWebApplicationContext} for actual creation
 	 * of the context. Can be overridden in subclasses.
 	 * @return the WebApplicationContext instance
 	 * @see #FrameworkServlet(WebApplicationContext)
 	 * @see #setContextClass
 	 * @see #setContextConfigLocation
 	 */
 	protected WebApplicationContext initWebApplicationContext() {
 		//从ServletContext中获取根上下文，作为MVC的双亲上下文
 		WebApplicationContext rootContext =
 				WebApplicationContextUtils.getWebApplicationContext(getServletContext());
 		WebApplicationContext wac = null;
 
 		if (this.webApplicationContext != null) {
 			// A context instance was injected at construction time -> use it
 			wac = this.webApplicationContext;
 			if (wac instanceof ConfigurableWebApplicationContext) {
 				ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
 				if (!cwac.isActive()) {
 					// The context has not yet been refreshed -> provide services such as
 					// setting the parent context, setting the application context id, etc
 					if (cwac.getParent() == null) {
 						// The context instance was injected without an explicit parent -> set
 						// the root application context (if any; may be null) as the parent
 						cwac.setParent(rootContext);
 					}
 					configureAndRefreshWebApplicationContext(cwac);
 				}
 			}
 		}
 		if (wac == null) {
 			// No context instance was injected at construction time -> see if one
 			// has been registered in the servlet context. If one exists, it is assumed
 			// that the parent context (if any) has already been set and that the
 			// user has performed any initialization such as setting the context id
 			wac = findWebApplicationContext();
 		}
 		if (wac == null) {
 			// No context instance is defined for this servlet -> create a local one
 			wac = createWebApplicationContext(rootContext);
 		}
 
 		if (!this.refreshEventReceived) {
 			// Either the context is not a ConfigurableApplicationContext with refresh
 			// support or the context injected at construction time had already been
 			// refreshed -> trigger initial onRefresh manually here.
 			onRefresh(wac);
 		}
 
 		if (this.publishContext) {
 			// Publish the context as a servlet context attribute.
 			//把当前建立的上下文放到ServletContext中，属性名是与当前的Servlet相关的
 			String attrName = getServletContextAttributeName();
 			getServletContext().setAttribute(attrName, wac);
 			if (this.logger.isDebugEnabled()) {
 				this.logger.debug("Published WebApplicationContext of servlet '" + getServletName() +
 						"' as ServletContext attribute with name [" + attrName + "]");
 			}
 		}
 
 		return wac;
 	}

MVC的初始化

/**
 	 * Initialize the strategy objects that this servlet uses.
 	 * May be overridden in subclasses in order to initialize further strategy objects.
 	 */
 	protected void initStrategies(ApplicationContext context) {
 		initMultipartResolver(context);
 		initLocaleResolver(context);
 		initThemeResolver(context);
 		initHandlerMappings(context);
 		initHandlerAdapters(context);
 		initHandlerExceptionResolvers(context);
 		initRequestToViewNameTranslator(context);
 		initViewResolvers(context);
 		initFlashMapManager(context);
 	}

initHanderMapping初始化过程：

/**
 	 * Initialize the HandlerMappings used by this class.
 	 * 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) {
 			// Find all HandlerMappings in the ApplicationContext, including ancestor contexts.
 			//导入所有的HanderMapping Bean，可能在Dispatcher的IOC容器内，也有可能在在其双亲上下文中
 			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 {
 			//可以根据名称从当前的IOC容器内获取handerMapping
 			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.
 			}
 		}
 		// Ensure we have at least one HandlerMapping, by registering
 		// a default HandlerMapping if no other mappings are found.
 		//如果没有则设置一个默认的HanderMapping
 		if (this.handlerMappings == null) {
 			this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);
 			if (logger.isDebugEnabled()) {
 				logger.debug("No HandlerMappings found in servlet '" + getServletName() + "': using default");
 			}
 		}
 	}

HanderMapping：

在初始化完成的时候，上下文环境已经加载了所有的HanderMapping,存放着HTTP请求对应的数据。这些数据被存放在一个List，然后被排序

以SimpleUrlHanderMapping来分析HanderMapping的设计和实现。在SimpleUrlHanderMapping中定义了一个map来持有一系列的映射关系。

在HanderMappping接口总定义了一个geHander方法，通过这个方法来获取与HTTP请求对应的HanderExecutionChain,

这个HanderExceutionChain实现看起来比较简洁，它有一个Interceptor和一个hander对象，这个hander对象实际上是HTTP请求的Controller，它还有一个拦截器链。

public interface HandlerMapping {
 
 	/**
 	 * Name of the {@link HttpServletRequest} attribute that contains the path
 	 * within the handler mapping, in case of a pattern match, or the full
 	 * relevant URI (typically within the DispatcherServlet's mapping) else.
 	 * Note: This attribute is not required to be supported by all
 	 * HandlerMapping implementations. URL-based HandlerMappings will
 	 * typically support it, but handlers should not necessarily expect
 	 * this request attribute to be present in all scenarios.
 	 */
 	String PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE = HandlerMapping.class.getName() + ".pathWithinHandlerMapping";
 
 	/**
 	 * Name of the {@link HttpServletRequest} attribute that contains the
 	 * best matching pattern within the handler mapping.
 	 * Note: This attribute is not required to be supported by all
 	 * HandlerMapping implementations. URL-based HandlerMappings will
 	 * typically support it, but handlers should not necessarily expect
 	 * this request attribute to be present in all scenarios.
 	 */
 	String BEST_MATCHING_PATTERN_ATTRIBUTE = HandlerMapping.class.getName() + ".bestMatchingPattern";
 
 	/**
 	 * Name of the boolean {@link HttpServletRequest} attribute that indicates
 	 * whether type-level mappings should be inspected.
 	 * Note: This attribute is not required to be supported by all
 	 * HandlerMapping implementations.
 	 */
 	String INTROSPECT_TYPE_LEVEL_MAPPING = HandlerMapping.class.getName() + ".introspectTypeLevelMapping";
 
 	/**
 	 * Name of the {@link HttpServletRequest} attribute that contains the URI
 	 * templates map, mapping variable names to values.
 	 * Note: This attribute is not required to be supported by all
 	 * HandlerMapping implementations. URL-based HandlerMappings will
 	 * typically support it, but handlers should not necessarily expect
 	 * this request attribute to be present in all scenarios.
 	 */
 	String URI_TEMPLATE_VARIABLES_ATTRIBUTE = HandlerMapping.class.getName() + ".uriTemplateVariables";
 
 	/**
 	 * Name of the {@link HttpServletRequest} attribute that contains a map with
 	 * URI matrix variables.
 	 * Note: This attribute is not required to be supported by all
 	 * HandlerMapping implementations and may also not be present depending on
 	 * whether the HandlerMapping is configured to keep matrix variable content
 	 * in the request URI.
 	 */
 	String MATRIX_VARIABLES_ATTRIBUTE = HandlerMapping.class.getName() + ".matrixVariables";
 
 	/**
 	 * Name of the {@link HttpServletRequest} attribute that contains the set of
 	 * producible MediaTypes applicable to the mapped handler.
 	 * Note: This attribute is not required to be supported by all
 	 * HandlerMapping implementations. Handlers should not necessarily expect
 	 * this request attribute to be present in all scenarios.
 	 */
 	String PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE = HandlerMapping.class.getName() + ".producibleMediaTypes";
 
 	/**
 	 * Return a handler and any interceptors for this request. The choice may be made
 	 * on request URL, session state, or any factor the implementing class chooses.
 	 * The returned HandlerExecutionChain contains a handler Object, rather than
 	 * even a tag interface, so that handlers are not constrained in any way.
 	 * For example, a HandlerAdapter could be written to allow another framework's
 	 * handler objects to be used.
 	 * Returns {@code null} if no match was found. This is not an error.
 	 * The DispatcherServlet will query all registered HandlerMapping beans to find
 	 * a match, and only decide there is an error if none can find a handler.
 	 * @param request current HTTP request
 	 * @return a HandlerExecutionChain instance containing handler object and
 	 * any interceptors, or {@code null} if no mapping found
 	 * @throws Exception if there is an internal error
 	 */
 	HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception;
 
 }

public class HandlerExecutionChain {
 
 	private static final Log logger = LogFactory.getLog(HandlerExecutionChain.class);
 
 	private final Object handler;
 
 	private HandlerInterceptor[] interceptors;
 
 	private List<HandlerInterceptor> interceptorList;
 
 	private int interceptorIndex = -1;
 
 
 	/**
 	 * Create a new HandlerExecutionChain.
 	 * @param handler the handler object to execute
 	 */
 	public HandlerExecutionChain(Object handler) {
 		this(handler, null);
 	}
 
 	/**
 	 * Create a new HandlerExecutionChain.
 	 * @param handler the handler object to execute
 	 * @param interceptors the array of interceptors to apply
 	 * (in the given order) before the handler itself executes
 	 */
 	public HandlerExecutionChain(Object handler, HandlerInterceptor[] interceptors) {
 		if (handler instanceof HandlerExecutionChain) {
 			HandlerExecutionChain originalChain = (HandlerExecutionChain) handler;
 			this.handler = originalChain.getHandler();
 			this.interceptorList = new ArrayList<HandlerInterceptor>();
 			CollectionUtils.mergeArrayIntoCollection(originalChain.getInterceptors(), this.interceptorList);
 			CollectionUtils.mergeArrayIntoCollection(interceptors, this.interceptorList);
 		}
 		else {
 			this.handler = handler;
 			this.interceptors = interceptors;
 		}
 	}
 
 	/**
 	 * Return the handler object to execute.
 	 * @return the handler object
 	 */
 	public Object getHandler() {
 		return this.handler;
 	}
 
 	public void addInterceptor(HandlerInterceptor interceptor) {
 		initInterceptorList();
 		this.interceptorList.add(interceptor);
 	}
 
 	public void addInterceptors(HandlerInterceptor[] interceptors) {
 		if (interceptors != null) {
 			initInterceptorList();
 			this.interceptorList.addAll(Arrays.asList(interceptors));
 		}
 	}
 
 	private void initInterceptorList() {
 		if (this.interceptorList == null) {
 			this.interceptorList = new ArrayList<HandlerInterceptor>();
 		}
 		if (this.interceptors != null) {
 			this.interceptorList.addAll(Arrays.asList(this.interceptors));
 			this.interceptors = null;
 		}
 	}
 
 	/**
 	 * Return the array of interceptors to apply (in the given order).
 	 * @return the array of HandlerInterceptors instances (may be {@code null})
 	 */
 	public HandlerInterceptor[] getInterceptors() {
 		if (this.interceptors == null && this.interceptorList != null) {
 			this.interceptors = this.interceptorList.toArray(new HandlerInterceptor[this.interceptorList.size()]);
 		}
 		return this.interceptors;
 	}
 
 	/**
 	 * Apply preHandle methods of registered interceptors.
 	 * @return {@code true} if the execution chain should proceed with the
 	 * next interceptor or the handler itself. Else, DispatcherServlet assumes
 	 * that this interceptor has already dealt with the response itself.
 	 */
 	boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
 		if (getInterceptors() != null) {
 			for (int i = 0; i < getInterceptors().length; i++) {
 				HandlerInterceptor interceptor = getInterceptors()[i];
 				if (!interceptor.preHandle(request, response, this.handler)) {
 					triggerAfterCompletion(request, response, null);
 					return false;
 				}
 				this.interceptorIndex = i;
 			}
 		}
 		return true;
 	}
 
 	/**
 	 * Apply postHandle methods of registered interceptors.
 	 */
 	void applyPostHandle(HttpServletRequest request, HttpServletResponse response, ModelAndView mv) throws Exception {
 		if (getInterceptors() == null) {
 			return;
 		}
 		for (int i = getInterceptors().length - 1; i >= 0; i--) {
 			HandlerInterceptor interceptor = getInterceptors()[i];
 			interceptor.postHandle(request, response, this.handler, mv);
 		}
 	}
 
 	/**
 	 * Trigger afterCompletion callbacks on the mapped HandlerInterceptors.
 	 * Will just invoke afterCompletion for all interceptors whose preHandle invocation
 	 * has successfully completed and returned true.
 	 */
 	void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, Exception ex)
 			throws Exception {
 
 		if (getInterceptors() == null) {
 			return;
 		}
 		for (int i = this.interceptorIndex; i >= 0; i--) {
 			HandlerInterceptor interceptor = getInterceptors()[i];
 			try {
 				interceptor.afterCompletion(request, response, this.handler, ex);
 			}
 			catch (Throwable ex2) {
 				logger.error("HandlerInterceptor.afterCompletion threw exception", ex2);
 			}
 		}
 	}
 
 	/**
 	 * Apply afterConcurrentHandlerStarted callback on mapped AsyncHandlerInterceptors.
 	 */
 	void applyAfterConcurrentHandlingStarted(HttpServletRequest request, HttpServletResponse response) {
 		if (getInterceptors() == null) {
 			return;
 		}
 		for (int i = getInterceptors().length - 1; i >= 0; i--) {
 			if (interceptors[i] instanceof AsyncHandlerInterceptor) {
 				try {
 					AsyncHandlerInterceptor asyncInterceptor = (AsyncHandlerInterceptor) this.interceptors[i];
 					asyncInterceptor.afterConcurrentHandlingStarted(request, response, this.handler);
 				}
 				catch (Throwable ex) {
 					logger.error("Interceptor [" + interceptors[i] + "] failed in afterConcurrentHandlingStarted", ex);
 				}
 			}
 		}
 	}
 
 	/**
 	 * Delegates to the handler's {@code toString()}.
 	 */
 	@Override
 	public String toString() {
 		if (this.handler == null) {
 			return "HandlerExecutionChain with no handler";
 		}
 		StringBuilder sb = new StringBuilder();
 		sb.append("HandlerExecutionChain with handler [").append(this.handler).append("]");
 		if (!CollectionUtils.isEmpty(this.interceptorList)) {
 			sb.append(" and ").append(this.interceptorList.size()).append(" interceptor");
 			if (this.interceptorList.size() > 1) {
 				sb.append("s");
 			}
 		}
 		return sb.toString();
 	}
 
 }

SimpleUrlHandlerMapping：

/**
    	 * Calls the {@link #registerHandlers} method in addition to the
    	 * superclass's initialization.
    	 */
    	@Override
    	public void initApplicationContext() throws BeansException {
    		super.initApplicationContext();
    		registerHandlers(this.urlMap);
    	}

/**
 	 * Register all handlers specified in the URL map for the corresponding paths.
 	 * @param urlMap Map with URL paths as keys and handler beans or bean names as values
 	 * @throws BeansException if a handler couldn't be registered
 	 * @throws IllegalStateException if there is a conflicting handler registered
 	 */
 	protected void registerHandlers(Map<String, Object> urlMap) throws BeansException {
 		if (urlMap.isEmpty()) {
 			logger.warn("Neither 'urlMap' nor 'mappings' set on SimpleUrlHandlerMapping");
 		}
 		else {
 			for (Map.Entry<String, Object> entry : urlMap.entrySet()) {
 				String url = entry.getKey();
 				Object handler = entry.getValue();
 				// Prepend with slash if not already present.
 				if (!url.startsWith("/")) {
 					url = "/" + url;
 				}
 				// Remove whitespace from handler bean name.
 				if (handler instanceof String) {
 					handler = ((String) handler).trim();
 				}
 				registerHandler(url, handler);
 			}
 		}
 	}

/**
    	 * Register the specified handler for the given URL path.
    	 * @param urlPath the URL the bean should be mapped to
    	 * @param handler the handler instance or handler bean name String
    	 * (a bean name will automatically be resolved into the corresponding handler bean)
    	 * @throws BeansException if the handler couldn't be registered
    	 * @throws IllegalStateException if there is a conflicting handler registered
    	 */
    	protected void registerHandler(String urlPath, Object handler) throws BeansException, IllegalStateException {
    		Assert.notNull(urlPath, "URL path must not be null");
    		Assert.notNull(handler, "Handler object must not be null");
    		Object resolvedHandler = handler;
    
    		// Eagerly resolve handler if referencing singleton via name.
         		//如果直接用bean Name来映射，那么直接从容器内获取
    		if (!this.lazyInitHandlers && handler instanceof String) {
    			String handlerName = (String) handler;
    			if (getApplicationContext().isSingleton(handlerName)) {
    				resolvedHandler = getApplicationContext().getBean(handlerName);
    			}
    		}
    
    		Object mappedHandler = this.handlerMap.get(urlPath);
    		if (mappedHandler != null) {
    			if (mappedHandler != resolvedHandler) {
    				throw new IllegalStateException(
    						"Cannot map " + getHandlerDescription(handler) + " to URL path [" + urlPath +
    						"]: There is already " + getHandlerDescription(mappedHandler) + " mapped.");
    			}
    		}
    		else {//如果URL是'/',把这个'/'设置的controller放到rootHander中
    			if (urlPath.equals("/")) {
    				if (logger.isInfoEnabled()) {
    					logger.info("Root mapping to " + getHandlerDescription(handler));
    				}
    				setRootHandler(resolvedHandler);
    			}//如果URL是'/*',把这个'/'设置的controller放到defaultHander中
    			else if (urlPath.equals("/*")) {
    				if (logger.isInfoEnabled()) {
    					logger.info("Default mapping to " + getHandlerDescription(handler));
    				}
    				setDefaultHandler(resolvedHandler);
    			}
    			else {//处理正常的URL
    				this.handlerMap.put(urlPath, resolvedHandler);
    				if (logger.isInfoEnabled()) {
    					logger.info("Mapped URL path [" + urlPath + "] onto " + getHandlerDescription(handler));
    				}
    			}
    		}
    	}

[SouthEast]: /images/20220823/3877b5e404364762b276de525413f2a6.png
[SouthEast 1]: /images/20220823/b811e72be5084f8692cfab52809ea21e.png