Spring MVC之HandlerMap 初始化

     DispatcherServlet请求处理请求的过程中，会发现getHandler实际上是调用AbstractUrlHandlerMapping.getHandlerInternal()。 通过对该段代码进行走读后发现，是通过handlermap.get(urlPath)获取匹配的handler的，那么该handlerMap是在什么时候进行初始化的呢？

   通过DefaultAnnotationHandlerMapping的继承关系可以去分析初始化的过程。

 

通过继承关系可以知道DefaultAnnotationHandlerMapping实现了ApplicationContextAware接口，这个接口的主要功能就是在Application初始化完成后会条用该接扩的setApplicationContext()方法。

 

AbstractDetectingUrlHandlerMapping是HandlerMapping初始化的关键入口，在初始化方法中首先调用父类的初始化方法，然后查找处理器。这个抽象类使用了模板方法模式，将具体的determineUrlsForHanlder方法延迟到子类中实现。

/**
 * Abstract implementation of the {@link org.springframework.web.servlet.HandlerMapping}
 * interface, detecting URL mappings for handler beans through introspection of all
 * defined beans in the application context.
 *
 * @author Juergen Hoeller
 * @since 2.5
 * @see #determineUrlsForHandler
 */
public abstract class AbstractDetectingUrlHandlerMapping extends AbstractUrlHandlerMapping {

	private boolean detectHandlersInAncestorContexts = false;


	/**
	 * Set whether to detect handler beans in ancestor ApplicationContexts.
	 * <p>Default is "false": Only handler beans in the current ApplicationContext
	 * will be detected, i.e. only in the context that this HandlerMapping itself
	 * is defined in (typically the current DispatcherServlet's context).
	 * <p>Switch this flag on to detect handler beans in ancestor contexts
	 * (typically the Spring root WebApplicationContext) as well.
	 */
	public void setDetectHandlersInAncestorContexts(boolean detectHandlersInAncestorContexts) {
		this.detectHandlersInAncestorContexts = detectHandlersInAncestorContexts;
	}


	/**
	 *在ApplicatonObjectSupport的setApplicationContext()方法中调用该方法
	 * Calls the {@link #detectHandlers()} method in addition to the
	 * superclass's initialization.
	 */
	@Override
	public void initApplicationContext() throws ApplicationContextException {
		// 调用父类的initApplicationContext()方法
		super.initApplicationContext();
		//查找Handler
		detectHandlers();
	}

	/**
	 * 注册所有能够从应用上下文中找到的handler
	 * Register all handlers found in the current ApplicationContext.
	 * <p>The actual URL determination for a handler is up to the concrete
	 * {@link #determineUrlsForHandler(String)} implementation. A bean for
	 * which no such URLs could be determined is simply not considered a handler.
	 * @throws org.springframework.beans.BeansException if the handler couldn't be registered
	 * @see #determineUrlsForHandler(String)
	 */
	protected void detectHandlers() throws BeansException {
		if (logger.isDebugEnabled()) {
			logger.debug("Looking for URL mappings in application context: " + getApplicationContext());
		}
		// 从上下文中获取所有的beanNames
		String[] beanNames = (this.detectHandlersInAncestorContexts ?
				BeanFactoryUtils.beanNamesForTypeIncludingAncestors(getApplicationContext(), Object.class) :
				getApplicationContext().getBeanNamesForType(Object.class));

		// 遍历所有BeanNames
		for (String beanName : beanNames) {
			//调用子类实现方法，判定这个bean 处理的url
			String[] urls = determineUrlsForHandler(beanName);
			// 如果这个bean可以处理url则将调用父类的registerHandler方法完成 url和handler映射关系的注册
			if (!ObjectUtils.isEmpty(urls)) {
				// URL paths found: Let's consider it a handler.
				registerHandler(urls, beanName);
			}
			else {
				if (logger.isDebugEnabled()) {
					logger.debug("Rejected bean name '" + beanName + "': no URL paths identified");
				}
			}
		}
	}


	/**
	 * Determine the URLs for the given handler bean.
	 * @param beanName the name of the candidate bean
	 * @return the URLs determined for the bean,
	 * or <code>null</code> or an empty array if none
	 */
	protected abstract String[] determineUrlsForHandler(String beanName);

}

 DefaultAnnotationHandlerMapping继承了AbstractDetectingUrlHandlerMapping,实现了父类的抽象方法，

首先查找这个类是否有RequestMapping的注解以及这个Bean中所有方法是否有这个注解

public class DefaultAnnotationHandlerMapping extends AbstractDetectingUrlHandlerMapping {

	static final String USE_DEFAULT_SUFFIX_PATTERN = DefaultAnnotationHandlerMapping.class.getName() + ".useDefaultSuffixPattern";

	private boolean useDefaultSuffixPattern = true;

	private final Map<Class<?>, RequestMapping> cachedMappings = new HashMap<Class<?>, RequestMapping>();


	/**
	 * Set whether to register paths using the default suffix pattern as well:
	 * i.e. whether "/users" should be registered as "/users.*" and "/users/" too.
	 * <p>Default is "true". Turn this convention off if you intend to interpret
	 * your <code>@RequestMapping</code> paths strictly.
	 * <p>Note that paths which include a ".xxx" suffix or end with "/" already will not be
	 * transformed using the default suffix pattern in any case.
	 */
	public void setUseDefaultSuffixPattern(boolean useDefaultSuffixPattern) {
		this.useDefaultSuffixPattern = useDefaultSuffixPattern;
	}


	/**
	 * Checks for presence of the {@link org.springframework.web.bind.annotation.RequestMapping}
	 * annotation on the handler class and on any of its methods.
	 */
	@Override
	protected String[] determineUrlsForHandler(String beanName) {
		ApplicationContext context = getApplicationContext();
		Class<?> handlerType = context.getType(beanName);
		RequestMapping mapping = context.findAnnotationOnBean(beanName, RequestMapping.class);
		if (mapping != null) {
			// @RequestMapping found at type level
			this.cachedMappings.put(handlerType, mapping);
			Set<String> urls = new LinkedHashSet<String>();
			String[] typeLevelPatterns = mapping.value();
			if (typeLevelPatterns.length > 0) {
				// @RequestMapping specifies paths at type level
				String[] methodLevelPatterns = determineUrlsForHandlerMethods(handlerType, true);
				for (String typeLevelPattern : typeLevelPatterns) {
					if (!typeLevelPattern.startsWith("/")) {
						typeLevelPattern = "/" + typeLevelPattern;
					}
					boolean hasEmptyMethodLevelMappings = false;
					for (String methodLevelPattern : methodLevelPatterns) {
						if (methodLevelPattern == null) {
							hasEmptyMethodLevelMappings = true;
						}
						else {
							String combinedPattern = getPathMatcher().combine(typeLevelPattern, methodLevelPattern);
							addUrlsForPath(urls, combinedPattern);
						}
					}
					if (hasEmptyMethodLevelMappings ||
							org.springframework.web.servlet.mvc.Controller.class.isAssignableFrom(handlerType)) {
						addUrlsForPath(urls, typeLevelPattern);
					}
				}
				return StringUtils.toStringArray(urls);
			}
			else {
				// actual paths specified by @RequestMapping at method level
				return determineUrlsForHandlerMethods(handlerType, false);
			}
		}
		else if (AnnotationUtils.findAnnotation(handlerType, Controller.class) != null) {
			// @RequestMapping to be introspected at method level
			return determineUrlsForHandlerMethods(handlerType, false);
		}
		else {
			return null;
		}
	}

	/**
	 * Derive URL mappings from the handler's method-level mappings.
	 * @param handlerType the handler type to introspect
	 * @param hasTypeLevelMapping whether the method-level mappings are nested
	 * within a type-level mapping
	 * @return the array of mapped URLs
	 */
	protected String[] determineUrlsForHandlerMethods(Class<?> handlerType, final boolean hasTypeLevelMapping) {
		//在该类中返回值一直是null
		String[] subclassResult = determineUrlsForHandlerMethods(handlerType);
		if (subclassResult != null) {
			return subclassResult;
		}
		// 创建一个set,之所以使用set就是set中不会有重复数据
		final Set<String> urls = new LinkedHashSet<String>();
		Set<Class<?>> handlerTypes = new LinkedHashSet<Class<?>>();
		//添加类以及所有接口
		handlerTypes.add(handlerType);
		handlerTypes.addAll(Arrays.asList(handlerType.getInterfaces()));
		// 遍历handlerTypes
		for (Class<?> currentHandlerType : handlerTypes) {
		// 反射处理
			ReflectionUtils.doWithMethods(currentHandlerType, new ReflectionUtils.MethodCallback() {
				public void doWith(Method method) {
				   // 获取所有该方法上的RequestMapping注解
					RequestMapping mapping = AnnotationUtils.findAnnotation(method, RequestMapping.class);
					// 如果存在RequestMapping注解
					if (mapping != null) {
						// 获取注解 value属性值
						String[] mappedPatterns = mapping.value();
						// 如果value的值不为空
						if (mappedPatterns.length > 0) {
							// 遍历mappedPatterns
							for (String mappedPattern : mappedPatterns) {
							    //如果hasTypeLevelMapping=false,同时mappedPattern不是以"/"开头则在其前面加上"/"
								if (!hasTypeLevelMapping && !mappedPattern.startsWith("/")) {
									mappedPattern = "/" + mappedPattern;
								}
								//将url添加在set中
								addUrlsForPath(urls, mappedPattern);
							}
						}
						else if (hasTypeLevelMapping) {
							// empty method-level RequestMapping
							urls.add(null);
						}
					}
				}
			}, ReflectionUtils.USER_DECLARED_METHODS);
		}
		return StringUtils.toStringArray(urls);
	}

	/**
	 * Derive URL mappings from the handler's method-level mappings.
	 * @param handlerType the handler type to introspect
	 * @return the array of mapped URLs
	 */
	protected String[] determineUrlsForHandlerMethods(Class<?> handlerType) {
		return null;
	}

	/**
	 * Add URLs and/or URL patterns for the given path.
	 * @param urls the Set of URLs for the current bean
	 * @param path the currently introspected path
	 */
	protected void addUrlsForPath(Set<String> urls, String path) {
		urls.add(path);
		if (this.useDefaultSuffixPattern && path.indexOf('.') == -1 && !path.endsWith("/")) {
			urls.add(path + ".*");
			urls.add(path + "/");
		}
	}


	/**
	 * Validate the given annotated handler against the current request.
	 * @see #validateMapping
	 */
	@Override
	protected void validateHandler(Object handler, HttpServletRequest request) throws Exception {
		RequestMapping mapping = this.cachedMappings.get(handler.getClass());
		if (mapping == null) {
			mapping = AnnotationUtils.findAnnotation(handler.getClass(), RequestMapping.class);
		}
		if (mapping != null) {
			validateMapping(mapping, request);
		}
		request.setAttribute(USE_DEFAULT_SUFFIX_PATTERN, this.useDefaultSuffixPattern);
	}

	/**
	 * Validate the given type-level mapping metadata against the current request,
	 * checking HTTP request method and parameter conditions.
	 * @param mapping the mapping metadata to validate
	 * @param request current HTTP request
	 * @throws Exception if validation failed
	 */
	protected void validateMapping(RequestMapping mapping, HttpServletRequest request) throws Exception {
		RequestMethod[] mappedMethods = mapping.method();
		if (!ServletAnnotationMappingUtils.checkRequestMethod(mappedMethods, request)) {
			String[] supportedMethods = new String[mappedMethods.length];
			for (int i = 0; i < mappedMethods.length; i++) {
				supportedMethods[i] = mappedMethods[i].name();
			}
			throw new HttpRequestMethodNotSupportedException(request.getMethod(), supportedMethods);
		}

		String[] mappedParams = mapping.params();
		if (!ServletAnnotationMappingUtils.checkParameters(mappedParams, request)) {
			throw new UnsatisfiedServletRequestParameterException(mappedParams, request.getParameterMap());
		}

		String[] mappedHeaders = mapping.headers();
		if (!ServletAnnotationMappingUtils.checkHeaders(mappedHeaders, request)) {
			throw new ServletRequestBindingException("Header conditions "" +
					StringUtils.arrayToDelimitedString(mappedHeaders, ", ") +
					"" not met for actual request");
		}
	}

	@Override
	protected boolean supportsTypeLevelMappings() {
		return true;
	}
}

 

public abstract class WebApplicationObjectSupport extends ApplicationObjectSupport
		implements ServletContextAware {

	private ServletContext servletContext;

	//由于该类实现了ServletContextAware接口，在ServletContext初始化完成后，调用该方法
	public final void setServletContext(ServletContext servletContext) {
		if (servletContext != this.servletContext) {
			this.servletContext = servletContext;
			if (servletContext != null) {
				initServletContext(servletContext);
			}
		}
	}

	@Override
	protected boolean isContextRequired() {
		return true;
	}

	/**
	 * 在ApplicationContext初始完成后调用该方法，如果已用上下文是WebApplicationContext则调用initServeltContext
	 */
	@Override
	protected void initApplicationContext(ApplicationContext context) {
		// 调用父类initApplicationContext，也就是调用ApplicationObjectSupport.initApplictionContext()方法
		super.initApplicationContext(context);
		if (this.servletContext == null && context instanceof WebApplicationContext) {
			this.servletContext = ((WebApplicationContext) context).getServletContext();
			if (this.servletContext != null) {
				// 模板方法模式，具体实现延迟到子类中进行
				initServletContext(this.servletContext);
			}
		}
	}

	/**
	 * Subclasses may override this for custom initialization based
	 * on the ServletContext that this application object runs in.
	 * <p>The default implementation is empty. Called by
	 * {@link #initApplicationContext(org.springframework.context.ApplicationContext)}
	 * as well as {@link #setServletContext(javax.servlet.ServletContext)}.
	 * @param servletContext the ServletContext that this application object runs in
	 * (never <code>null</code>)
	 */
	protected void initServletContext(ServletContext servletContext) {
	}