Spring MVC : HandlerMappingIntrospector

概述

这是一个Spring MVC助手类，用于集合应用所配置的HandlerMapping(url pattern和请求处理handler之间的映射)表，用于获取针对某个请求的如下信息 :

1. getMatchableHandlerMapping(javax.servlet.http.HttpServletRequest)

   寻找能处理指定请求的HandlerMapping，如果找不到，返回null;如果找到的是一个MatchableHandlerMapping，则返回；如果找得到当并不是MatchableHandlerMapping，则抛出异常IllegalStateException。

2. getCorsConfiguration(javax.servlet.http.HttpServletRequest)

   获取针对指定请求的CORS配置，封装为CorsConfiguration。如果不存在相应配置，返回null。

使用

1. 作为CorsConfigurationSource使用

    // 配置类 WebMvcConfigurationSupport
	@Bean
	@Lazy
	public HandlerMappingIntrospector mvcHandlerMappingIntrospector() {
		return new HandlerMappingIntrospector();
	}

源代码

源代码版本 Spring Web MVC 5.1.5.RELEASE

package org.springframework.web.servlet.handler;

// 省略 imports


public class HandlerMappingIntrospector
		implements CorsConfigurationSource, ApplicationContextAware, InitializingBean {

	@Nullable
	private ApplicationContext applicationContext;

	@Nullable
	private List<HandlerMapping> handlerMappings;


	/**
	 * Constructor for use with ApplicationContextAware.
	 */
	public HandlerMappingIntrospector() {
	}

	/**
	 * Constructor that detects the configured {@code HandlerMapping}s in the
	 * given {@code ApplicationContext} or falls back on
	 * "DispatcherServlet.properties" like the {@code DispatcherServlet}.
	 * @deprecated as of 4.3.12, in favor of {@link #setApplicationContext}
	 */
	@Deprecated
	public HandlerMappingIntrospector(ApplicationContext context) {
		this.handlerMappings = initHandlerMappings(context);
	}


	/**
	 * Return the configured HandlerMapping's.
	 */
	public List<HandlerMapping> getHandlerMappings() {
		return (this.handlerMappings != null ? this.handlerMappings : Collections.emptyList());
	}


	@Override
	public void setApplicationContext(ApplicationContext applicationContext) {
		this.applicationContext = applicationContext;
	}

   // InitializingBean 接口约定的方法，用于获取容器中定义的所有类型为 HandlerMapping 的 bean,
   // 或者获取缺省定义的类型为 HandlerMapping 的 bean
	@Override
	public void afterPropertiesSet() {
		if (this.handlerMappings == null) {
			Assert.notNull(this.applicationContext, "No ApplicationContext");
			this.handlerMappings = initHandlerMappings(this.applicationContext);
		}
	}


	/**
	 * Find the {@link HandlerMapping} that would handle the given request and
	 * return it as a {@link MatchableHandlerMapping} that can be used to test
	 * request-matching criteria.
	 * <p>If the matching HandlerMapping is not an instance of
	 * {@link MatchableHandlerMapping}, an IllegalStateException is raised.
	 * @param request the current request
	 * @return the resolved matcher, or {@code null}
	 * @throws Exception if any of the HandlerMapping's raise an exception
	 */
	@Nullable
	public MatchableHandlerMapping getMatchableHandlerMapping(HttpServletRequest request) throws Exception {
		Assert.notNull(this.handlerMappings, "Handler mappings not initialized");
		HttpServletRequest wrapper = new RequestAttributeChangeIgnoringWrapper(request);
		for (HandlerMapping handlerMapping : this.handlerMappings) {
			Object handler = handlerMapping.getHandler(wrapper);
			if (handler == null) {
				continue;
			}
			if (handlerMapping instanceof MatchableHandlerMapping) {
				return ((MatchableHandlerMapping) handlerMapping);
			}
			throw new IllegalStateException("HandlerMapping is not a MatchableHandlerMapping");
		}
		return null;
	}


    // 获取某个 request 请求对应的 CorsConfiguration
    // 1. 从 handlerMappings 中找到该请求对应的 handler, 形式为 HandlerExecutionChain;
    // 2. 检索 HandlerExecutionChain 中所有的 
	@Override
	@Nullable
	public CorsConfiguration getCorsConfiguration(HttpServletRequest request) {
		Assert.notNull(this.handlerMappings, "Handler mappings not initialized");
		HttpServletRequest wrapper = new RequestAttributeChangeIgnoringWrapper(request);
		for (HandlerMapping handlerMapping : this.handlerMappings) {
			HandlerExecutionChain handler = null;
			try {
				handler = handlerMapping.getHandler(wrapper);
			}
			catch (Exception ex) {
				// Ignore
			}
			if (handler == null) {
				continue;
			}
			if (handler.getInterceptors() != null) {
				for (HandlerInterceptor interceptor : handler.getInterceptors()) {
					if (interceptor instanceof CorsConfigurationSource) {
						return ((CorsConfigurationSource) interceptor).getCorsConfiguration(wrapper);
					}
				}
			}
			if (handler.getHandler() instanceof CorsConfigurationSource) {
				return ((CorsConfigurationSource) handler.getHandler()).getCorsConfiguration(wrapper);
			}
		}
		return null;
	}


	private static List<HandlerMapping> initHandlerMappings(ApplicationContext applicationContext) {
       // 获取容器中所有类型为 HandlerMapping 的 bean
		Map<String, HandlerMapping> beans = BeanFactoryUtils.beansOfTypeIncludingAncestors(
				applicationContext, HandlerMapping.class, true, false);
		if (!beans.isEmpty()) {
			List<HandlerMapping> mappings = new ArrayList<>(beans.values());
			AnnotationAwareOrderComparator.sort(mappings);
			return Collections.unmodifiableList(mappings);
		}
        
       // 容器中不存在类型为 HandlerMapping 的 bean,
       // 此时使用 initFallback 创建 DispatcherServlet.properties 文件中
       // 缺省定义的类型为 HandlerMapping 的 bean
		return Collections.unmodifiableList(initFallback(applicationContext));
	}

	private static List<HandlerMapping> initFallback(ApplicationContext applicationContext) {
		Properties props;
		String path = "DispatcherServlet.properties";
		try {
			Resource resource = new ClassPathResource(path, DispatcherServlet.class);
			props = PropertiesLoaderUtils.loadProperties(resource);
		}
		catch (IOException ex) {
			throw new IllegalStateException("Could not load '" + path + "': " + ex.getMessage());
		}

		String value = props.getProperty(HandlerMapping.class.getName());
		String[] names = StringUtils.commaDelimitedListToStringArray(value);
		List<HandlerMapping> result = new ArrayList<>(names.length);
		for (String name : names) {
			try {
				Class<?> clazz = ClassUtils.forName(name, DispatcherServlet.class.getClassLoader());
              // 使用容器创建 bean，该动作会使所创建的 bean 经历相应的生命周期处理，比如初始化，属性设置等等  
				Object mapping = applicationContext.getAutowireCapableBeanFactory().createBean(clazz);
				result.add((HandlerMapping) mapping);
			}
			catch (ClassNotFoundException ex) {
				throw new IllegalStateException("Could not find default HandlerMapping [" + name + "]");
			}
		}
		return result;
	}


	/**
	 * Request wrapper that ignores request attribute changes.
     * 定义一个给当前 HandlerMappingIntrospector 使用的 HttpServletRequestWrapper，
     * 其方法 setAttribute 实现为空，主要是用于避免属性修改，也就是保持对所访问的 request 不做修改
	 */
	private static class RequestAttributeChangeIgnoringWrapper extends HttpServletRequestWrapper {

		public RequestAttributeChangeIgnoringWrapper(HttpServletRequest request) {
			super(request);
		}

		@Override
		public void setAttribute(String name, Object value) {
			// Ignore attribute change...
		}
	}

}