SpringFramework之HandlerMapping的俩个默认实现类的初始化

Spring MVC HandlerMapping解析

最新推荐文章于 2024-06-28 11:50:04 发布

weixin_34191734

最新推荐文章于 2024-06-28 11:50:04 发布

阅读量289

点赞数

CC 4.0 BY-SA版权

文章标签： java 测试

原文链接：https://my.oschina.net/u/2518341/blog/1827389

本文详细解析了Spring MVC中HandlerMapping的工作原理，包括BeanNameUrlHandlerMapping、SimpleUrlHandlerMapping和DefaultAnnotationHandlerMapping的实现机制及用法。通过源码分析帮助理解Spring MVC的请求映射过程。

2019独角兽企业重金招聘Python工程师标准>>>

注：SpringFramework的版本是4.3.x。

1.HandlerMapping的俩个默认实现类

们由DispatcherServlet的初始化简析得知默认的HandlerMapping是BeanNameUrlHandlerMapping和DefaultAnnotationHandlerMapping，这俩个类的继承图如下图2、图3所示，

图2 BeanNameUrlHandlerMapping的类继承图

图3 DefaultAnnotationHandlerMapping的类继承图

BeanNameUrlHandlerMapping是spring-webmvc模块的，DefaultAnnotationHandlerMapping是spring-webmvc-porlet的。我们主要分析这俩个HandlerMapping。

BeanNameUrlHandlerMapping的用法如下，

<bean class="org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping"/>
<bean name="/hello" class="com.mjduan.project.example8_aop.HelloController"/>

HelloController的源码如下，

public class HelloController extends AbstractController {
    @Override
    protected ModelAndView handleRequestInternal(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse) throws Exception {
        return null;
    }
}

BeanNameUrlHandlerMapping初始化的时序图，如下图4所示：

图4 BeanNameUrlHandlerMapping的初始化时序图

图3的说明：由于ApplicationObjectSupport实现了ApplicationContextAware接口，所有在执行setApplicationContext的时候会初始化AbstractUrlHandlerMapping的属性handlerMap。

图4的步骤6中，会从applicationContext中取出所有的MappedInterceptor，放到AbstractHandlerMapping的属性adaptedInterceptors中，这些MappedInterceptor是HandlerInterceptor的子类，在构造HandlerExecutionChain时用到。

我们再来分析AbstractDetectingUrlHandlerMapping的detectHandlers方法，源码如下List-1所示，

List-1 AbstractDetectingUrlHandlerMapping的detectHandlers()源码

protected void detectHandlers() throws BeansException {
	if (logger.isDebugEnabled()) {
		logger.debug("Looking for URL mappings in application context: " + getApplicationContext());
	}
	String[] beanNames = (this.detectHandlersInAncestorContexts ?
			BeanFactoryUtils.beanNamesForTypeIncludingAncestors(getApplicationContext(), Object.class) :
			getApplicationContext().getBeanNamesForType(Object.class));

	// Take any bean name that we can determine URLs for.
	for (String beanName : beanNames) {
		String[] urls = determineUrlsForHandler(beanName);
		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");
			}
		}
	}
}

determineUrlsForHandler方法的实现是在BeanNameUrlHandlerMapping中，源码如下List-2所示，

List-2 BeanNameUrlHandlerMapping的determineUrlsForHandler方法源码

public class BeanNameUrlHandlerMapping extends AbstractDetectingUrlHandlerMapping {

	/**
	 * Checks name and aliases of the given bean for URLs, starting with "/".
	 */
	@Override
	protected String[] determineUrlsForHandler(String beanName) {
		List<String> urls = new ArrayList<String>();
		if (beanName.startsWith("/")) {
			urls.add(beanName);
		}
		String[] aliases = getApplicationContext().getAliases(beanName);
		for (String alias : aliases) {
			if (alias.startsWith("/")) {
				urls.add(alias);
			}
		}
		return StringUtils.toStringArray(urls);
	}
}

由List-1的代码可知，从applicationContext中取出所有的beanName，之后遍历所有的beanName，如果该beanName以"/"开头，则将这个beanName视为url，记录。

一般情况下，我们不会使用BeanNameUrlHandlerMapping的，BeanNameUrlHandlerMapping使用起来感觉不是很灵活。

3.SimpleUrlHandlerMapping的用法

SimpleUrlHandlerMapping的一般使用方式如下，prop中key的值，是spring bean。这种是以前的用法，现在基本都使用注解的方式了，很少用这种了。注：下面这段代码来源: https://blog.youkuaiyun.com/trigl/article/details/50494492

<bean
    class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
    <property name="mappings">
        <props>
            <prop key="/upfile.do">upfile</prop>
            <prop key="/upfiles.do">upfiles</prop>
            <prop key="/extjs.do">SpringMVC</prop>
            <prop key="/show.do">show</prop>
        </props>
    </property>
</bean>

4.DefaultAnnotationHandlerMapping的分析

List-3 DefaultAnnotationHandlerMapping的initApplicationContext()源码

@Override
public void initApplicationContext() throws BeansException {
	super.initApplicationContext();
	detectHandlers();
}

/**
 * Register all handlers specified in the Portlet mode map for the corresponding modes.
 * @throws org.springframework.beans.BeansException if the handler couldn't be registered
 */
protected void detectHandlers() throws BeansException {
	ApplicationContext context = getApplicationContext();
	String[] beanNames = context.getBeanNamesForType(Object.class);
	for (String beanName : beanNames) {
		Class<?> handlerType = context.getType(beanName);
		RequestMapping mapping = context.findAnnotationOnBean(beanName, RequestMapping.class);
		if (mapping != null) {
			// @RequestMapping found at type level
			String[] modeKeys = mapping.value();
			String[] params = mapping.params();
			boolean registerHandlerType = true;
			if (modeKeys.length == 0 || params.length == 0) {
				registerHandlerType = !detectHandlerMethods(handlerType, beanName, mapping);
			}
			if (registerHandlerType) {
				AbstractParameterMappingPredicate predicate = new TypeLevelMappingPredicate(
						params, mapping.headers(), mapping.method());
				for (String modeKey : modeKeys) {
					registerHandler(new PortletMode(modeKey), beanName, predicate);
				}
			}
		}
		else if (AnnotationUtils.findAnnotation(handlerType, Controller.class) != null) {
			detectHandlerMethods(handlerType, beanName, mapping);
		}
	}
}

从List-3中的detectHandlers可知，

先获取applicationContext中所有的beanName，而后获取其对应的Class<?>，判断类上是否有RequestMapping注解，有的话，进行解析，之后registerHandler。
若类上没有找到RequestMapping注解，则判断类上是否有Controller注解，如果有，那么执行detectHandlerMethods，这个方法的源码有点多，我只是给出部分，如下List-4所示:

List-4 DefaultAnnotationHandlerMapping的detectHandlerMethods方法源码

protected boolean detectHandlerMethods(Class<?> handlerType, final String beanName, final RequestMapping typeMapping) {
	final Set<Boolean> handlersRegistered = new HashSet<Boolean>(1);
	Set<Class<?>> handlerTypes = new LinkedHashSet<Class<?>>();
	handlerTypes.add(handlerType);
	handlerTypes.addAll(Arrays.asList(handlerType.getInterfaces()));
	for (Class<?> currentHandlerType : handlerTypes) {
		ReflectionUtils.doWithMethods(currentHandlerType, new ReflectionUtils.MethodCallback() {
			@Override
			public void doWith(Method method) {
				PortletRequestMappingPredicate predicate = null;
				String[] modeKeys = new String[0];
				String[] params = new String[0];
				if (typeMapping != null) {
					params = PortletAnnotationMappingUtils.mergeStringArrays(typeMapping.params(), params);
				}
				ActionMapping actionMapping = AnnotationUtils.findAnnotation(method, ActionMapping.class);
				RenderMapping renderMapping = AnnotationUtils.findAnnotation(method, RenderMapping.class);
				ResourceMapping resourceMapping = AnnotationUtils.findAnnotation(method, ResourceMapping.class);
				EventMapping eventMapping = AnnotationUtils.findAnnotation(method, EventMapping.class);
				RequestMapping requestMapping = AnnotationUtils.findAnnotation(method, RequestMapping.class);
				if (actionMapping != null) {
					params = PortletAnnotationMappingUtils.mergeStringArrays(params, actionMapping.params());
					predicate = new ActionMappingPredicate(actionMapping.name(), params);
				}
   ......

从List-4可知，detectHandlerMethods方法，对类的方法进行遍历，之后逐个处理每个方法。

DefaultAnnotationHandlerMapping处理的就是我们平时所用的基于注解的方式。

转载于:https://my.oschina.net/u/2518341/blog/1827389