SpringMVC HandlerAdapter创建加载过程

xml部分

如果开启xml注解会把RequestMappingHandlerAdapter.class 这个类加入到spring容器中，处理requestMapping这个注解的method，源码如下

public class MvcNamespaceHandler extends NamespaceHandlerSupport {

	@Override
	public void init() {
		registerBeanDefinitionParser("annotation-driven", new AnnotationDrivenBeanDefinitionParser());//开启注解
		registerBeanDefinitionParser("default-servlet-handler", new DefaultServletHandlerBeanDefinitionParser());
		registerBeanDefinitionParser("interceptors", new InterceptorsBeanDefinitionParser());
		registerBeanDefinitionParser("resources", new ResourcesBeanDefinitionParser());
		registerBeanDefinitionParser("view-controller", new ViewControllerBeanDefinitionParser());
		registerBeanDefinitionParser("redirect-view-controller", new ViewControllerBeanDefinitionParser());
		registerBeanDefinitionParser("status-controller", new ViewControllerBeanDefinitionParser());
		registerBeanDefinitionParser("view-resolvers", new ViewResolversBeanDefinitionParser());
		registerBeanDefinitionParser("tiles-configurer", new TilesConfigurerBeanDefinitionParser());
		registerBeanDefinitionParser("freemarker-configurer", new FreeMarkerConfigurerBeanDefinitionParser());
		registerBeanDefinitionParser("velocity-configurer", new VelocityConfigurerBeanDefinitionParser());
		registerBeanDefinitionParser("groovy-configurer", new GroovyMarkupConfigurerBeanDefinitionParser());
	}

}

class AnnotationDrivenBeanDefinitionParser implements BeanDefinitionParser {
	......
	@Override
	public BeanDefinition parse(Element element, ParserContext parserContext) {
						.....
		String uriCompContribName = MvcUriComponentsBuilder.MVC_URI_COMPONENTS_CONTRIBUTOR_BEAN_NAME;
		RootBeanDefinition uriCompContribDef = new RootBeanDefinition(CompositeUriComponentsContributorFactoryBean.class);
		uriCompContribDef.setSource(source);
		uriCompContribDef.getPropertyValues().addPropertyValue("handlerAdapter", handlerAdapterDef);
		uriCompContribDef.getPropertyValues().addPropertyValue("conversionService", conversionService);
		parserContext.getReaderContext().getRegistry().registerBeanDefinition(uriCompContribName, uriCompContribDef);
						.....
	
	}

	.....

}

接下来看初始化的时候

初始化的时候就是看 dispatcherservlet 中的

protected void initStrategies(ApplicationContext context) {
		initMultipartResolver(context);
		initLocaleResolver(context);
		initThemeResolver(context);
		initHandlerMappings(context);
		initHandlerAdapters(context); //初始化handleradapter
		initHandlerExceptionResolvers(context);
		initRequestToViewNameTranslator(context);
		initViewResolvers(context);
		initFlashMapManager(context);
	}

	private void initHandlerAdapters(ApplicationContext context) {
		this.handlerAdapters = null;

		if (this.detectAllHandlerAdapters) {//默认就是true，如果不设置的话
			// 在spring全部的上下文中寻找 所有HandlerAdapter
			Map<String, HandlerAdapter> matchingBeans =
					BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerAdapter.class, true, false);
			if (!matchingBeans.isEmpty()) {
				this.handlerAdapters = new ArrayList<HandlerAdapter>(matchingBeans.values());
				// HandlerAdapter是以顺序来判断的，所以要排序
				OrderComparator.sort(this.handlerAdapters);
			}
		}
		else {// 如果不加载spring中全部的handlerAdapter就加载默认的"handlerAdapter"到容器中
			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.
			}
		}

		// 终极方案，都没有就用配置文件中默认的3个handleradapter
		if (this.handlerAdapters == null) {
			this.handlerAdapters = getDefaultStrategies(context, HandlerAdapter.class);
			if (logger.isDebugEnabled()) {
				logger.debug("No HandlerAdapters found in servlet '" + getServletName() + "': using default");
			}
		}
	}

总结

这样基本上所有的我们配置，注册的handleradapter,都会加载并注册到mvc的组件中，如果有新的方式来设置adapter，只需要把他配置到spring中，mvc会自己去发现这些组件，并配置