SpringMVC源码总结（二）mvc:annotation-driven以及@Controller和@RequestMapping的那些事

上一篇文章让我们了解HandlerMapping和HandlerAdapter以及默认采取的策略，这篇文章就要讲述mvc:annotation-driven对默认策略的改变。它背后到底注册了哪些HandlerMapping和HandlerAdapter。

首先可以在DispatcherServlet的initStrategies方法中的initHandlerMappings和initHandlerAdapters中打上断点，来查看注册了哪些HandlerMapping和HandlerAdapter

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

目前我的spring版本是4.0.5。我查看的结果：
HandlerMapping：注册了 RequestMappingHandlerMapping和BeanNameUrlHandlerMapping
HandlerAdapter：注册了 RequestMappingHandlerAdapter、HttpRequestHandlerAdapter和SimpleControllerHandlerAdapter
这几个HandlerMapping和HandlerAdapter上文都提到过。
下面就要查看下具体的注册过程：
在xml文件中配置mvc:annotation-driven，肯定有一个专门的类来解析处理这个东西。
会有这样的一个接口BeanDefinitionParser，它只有一个方法：

public interface BeanDefinitionParser {

	/**
	 * Parse the specified {@link Element} and register the resulting
	 * {@link BeanDefinition BeanDefinition(s)} with the
	 * {@link org.springframework.beans.factory.xml.ParserContext#getRegistry() BeanDefinitionRegistry}
	 * embedded in the supplied {@link ParserContext}.
	 * <p>Implementations must return the primary {@link BeanDefinition} that results
	 * from the parse if they will ever be used in a nested fashion (for example as
	 * an inner tag in a {@code <property/>} tag). Implementations may return
	 * {@code null} if they will <strong>not</strong> be used in a nested fashion.
	 * @param element the element that is to be parsed into one or more {@link BeanDefinition BeanDefinitions}
	 * @param parserContext the object encapsulating the current state of the parsing process;
	 * provides access to a {@link org.springframework.beans.factory.support.BeanDefinitionRegistry}
	 * @return the primary {@link BeanDefinition}
	 */
	BeanDefinition parse(Element element, ParserContext parserContext);

}

它是用来专门处理<beans></beans>里面的配置元素。然后我们会找到这样的一个实现类AnnotationDrivenBeanDefinitionParser，它的文档介绍如下：

/**
 * 这里清清楚楚写着该类是专门处理 <mvc:annotation-driven/>标签的
 * A {@link BeanDefinitionParser} that provides the configuration for the
 * {@code <annotation-driven/>} MVC namespace  element.
 *
 * 这里说明了注册的HandlerMapping
 * <p>This class registers the following {@link HandlerMapping}s:</p>
 * <ul>
 * 	<li>{@link RequestMappingHandlerMapping}
 * 	ordered at 0 for mapping requests to annotated controller methods.
 * 	<li>{@link BeanNameUrlHandlerMapping}
 * 	ordered at 2 to map URL paths to controller bean names.
 * </ul>
 *
 * <p><strong>Note:</strong> Additional HandlerMappings may be registered
 * as a result of using the {@code <view-controller>} or the
 * {@code <resources>} MVC namespace elements.
 *
 * 这里说明了注册的HandlerAdapter
 * <p>This class registers the following {@link HandlerAdapter}s:
 * <ul>
 * 	<li>{@link RequestMappingHandlerAdapter}
 * 	for processing requests with annotated controller methods.
 * 	<li>{@link HttpRequestHandlerAdapter}
 * 	for processing requests with {@link HttpRequestHandler}s.
 * 	<li>{@link SimpleControllerHandlerAdapter}
 * 	for processing requests with interface-based {@link Controller}s.
 * </ul>
 *
 * <p>This class registers the following {@link HandlerExceptionResolver}s:
 * <ul>
 * 	<li>{@link ExceptionHandlerExceptionResolver} for handling exceptions
 * 	through @{@link ExceptionHandler} methods.
 * 	<li>{@link ResponseStatusExceptionResolver} for exceptions annotated
 * 	with @{@link ResponseStatus}.
 * 	<li>{@link DefaultHandlerExceptionResolver} for resolving known Spring
 * 	exception types
 * </ul>
 *
 * <p>Both the {@link RequestMappingHandlerAdapter} and the
 * {@link ExceptionHandlerExceptionResolver} are configured with instances of
 * the following by default:
 * <ul>
 * 	<li>A {@link ContentNegotiationManager}
 * 	<li>A {@link DefaultFormattingConversionService}
 * 	<li>A {@link org.springframework.validation.beanvalidation.LocalValidatorFactoryBean}
 * 	if a JSR-303 implementation is available on the classpath
 * 	<li>A range of {@link HttpMessageConverter}s depending on what 3rd party
 * 	libraries are available on the classpath.
 * </ul>
 *
 * @author Keith Donald
 * @author Juergen Hoeller
 * @author Arjen Poutsma
 * @author Rossen Stoyanchev
 * @author Brian Clozel
 * @since 3.0
 */
class AnnotationDrivenBeanDefinitionParser implements BeanDefinitionParser {
          //先省略，请详细看下它的文档介绍
}

上面的文档对mvc:annotation-driven注册的东西都有详细的说明。
具体看解析过程的代码的内容：

@Override
	public BeanDefinition parse(Element element, ParserContext parserContext) {
		Object source = parserContext.extractSource(element);

		//省略
		RootBeanDefinition handlerMappingDef = new RootBeanDefinition(RequestMappingHandlerMapping.class);
		
		RootBeanDefinition handlerAdapterDef = new RootBeanDefinition(RequestMappingHandlerAdapter.class);
		
            //省略，
		// Ensure BeanNameUrlHandlerMapping (SPR-8289) and default HandlerAdapters are not "turned off"
		MvcNamespaceUtils.registerDefaultComponents(parserContext, source);

		parserContext.popAndRegisterContainingComponent();

		return null;
	}

MvcNamespaceUtils.registerDefaultComponents的内容如下：

public static void registerDefaultComponents(ParserContext parserContext, Object source) {
		registerBeanNameUrlHandlerMapping(parserContext, source);
		registerHttpRequestHandlerAdapter(parserContext, source);
		registerSimpleControllerHandlerAdapter(parserContext, source);
	}

至此所注册的HandlerMapping和HandlerAdapter我们都找到了。
然后我们就可以体验下RequestMappingHandlerMapping和BeanNameUrlHandlerMapping，这两个HandlerMapping。由于上一篇文章已经体验过了BeanNameUrlHandlerMapping，接下来就要体验下RequestMappingHandlerMapping，然后你会发觉又有一系列的新名词走进我们的视野，需要我们去弄清楚。
先体验下：

首先还是web.xml的配置：

<!DOCTYPE web-app PUBLIC
 "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
 "http://java.sun.com/dtd/web-app_2_3.dtd" >

<web-app>
  <display-name>Archetype Created Web Application</display-name>
  <servlet>
		<servlet-name>mvc</servlet-name>
		<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
		<load-on-startup>1</load-on-startup>
	</servlet>

	<servlet-mapping>
		<servlet-name>mvc</servlet-name>
		<url-pattern>/*</url-pattern>
	</servlet-mapping>
</web-app>

最简单的配置，然后是[servlet-name]-servlet.xml，本工程即mvc-servlet.xml：

<?xml version="1.0" encoding="UTF-8" ?>
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:util="http://www.springframework.org/schema/util" xmlns:context="http://www.springframework.org/schema/context"
	xsi:schemaLocation="http://www.springframework.org/schema/beans
	http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
	http://www.springframework.org/schema/mvc
	http://www.springframework.org/schema/mvc/spring-mvc-3.1.xsd
	http://www.springframework.org/schema/util
	http://www.springframework.org/schema/util/spring-util-2.0.xsd
	http://www.springframework.org/schema/context 
	http://www.springframework.org/schema/context/spring-context-3.2.xsd">
	
	
	<mvc:annotation-driven/>
	
	<bean class="com.lg.mvc.StringAction"/>
	<bean name="/index" class="com.lg.mvc.HomeAction"></bean>
	
	
	<bean class="org.springframework.web.servlet.view.freemarker.FreeMarkerConfigurer">
		<property name="templateLoaderPath" value="/WEB-INF/views" />
		<property name="defaultEncoding" value="utf-8" />
		<property name="freemarkerSettings">
			<props>
				<prop key="locale">zh_CN</prop>
			</props>
		</property>
	</bean>
	<bean class="org.springframework.web.servlet.view.freemarker.FreeMarkerViewResolver">
		<property name="suffix" value=".html" />
		<property name="contentType" value="text/html;charset=utf-8" />
		<property name="requestContextAttribute" value="request" />
		<property name="exposeRequestAttributes" value="true" />
		<property name="exposeSessionAttributes" value="true" />
	</bean>
</beans>

开启了<mvc:annotation-driven/>，同时注册了两个bean。有RequestMappingHandlerMapping和RequestMappingHandlerAdapter作为后盾支持，然后我们就可以在bean中使用@Controller和@RequestMapping两个标签了。@Controller本身其实与@RequestMapping无关的，它只是@Component中的一个重要的标签而已，但是我们会在源码里看到它对RequestMappingHandlerMapping也是挺重要的，但不是必须的。这里简单说明下：RequestMappingHandlerMapping它会判断一个bean是否含有@Controller标签或者@RequestMapping，如果有其一则会将该bean纳入作为它的处理对象，之后会进一步处理该类上含有@RequestMapping注解的方法。这样做主要是由于@RequestMapping可以配置在类上（作为基础地址），也可以配置在方法上，我们有时候会在类上配置@RequestMapping，有时候又不会，所以只要类含有@Controller或者含有@RequestMapping，RequestMappingHandlerMapping都会将他们纳入自己的handler管辖范围。所以仅仅在方法中含有@RequestMapping注解是不被处理的，必须在类上加入@RequestMapping或者@Controller，而@Controller又不是必须的，你可以试验下，稍后会做源代码说明。下面继续，列出使用了@Controller和@RequestMapping注解的StringAction类

package com.lg.mvc;

import java.io.UnsupportedEncodingException;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseBody;

@Controller
public class StringAction {
	
	@ResponseBody
	@RequestMapping(value="/string",method=RequestMethod.GET)
	public String testMessageConverter(String name) throws UnsupportedEncodingException{
		System.out.println(name);
		return name;
	}
}

然后就可以运行一下，体验一下，先不要管乱码问题，这个问题引出了下一篇文章spring框架中的乱码问题。
运行结果如下：


证明整个流程跑通了。
首先@Controller使得StringAction这个handler纳入RequestMappingHandlerMapping管理，RequestMappingHandlerMapping会将这个handler和handler中的每一个含有@RequestMapping的方法都会构建成一个HandlerMethod对象，该类的构造函数为HandlerMethod(Object bean, Method method)，经过这样的包装之后将构造的HandlerMethod对象作为新的handler，然后进行选择适配器，进行方法调用，当RequestMappingHandlerAdapter判断是否support一个类时，就是依据当前的handlelr是否是HandlerMethod类型。若是则由RequestMappingHandlerAdapter来调度执行该handler（handler为HandlerMethod类型）的中的method方法。以上就是整个大体的流程。下面就要用代码来事实说话：
第一步要弄清RequestMappingHandlerMapping在初始化时是如何寻找它所管辖的bean。说说我找代码的具体流程：
RequestMappingHandlerMapping的父类AbstractHandlerMethodMapping在初始化时，会调用到这样的一个方法initHandlerMethods，在该方法中，遍历所有的bean然后判断他们是不是含有@Controller或者@RequestMapping注解：

/**
	 * Scan beans in the ApplicationContext, detect and register handler methods.
	 * @see #isHandler(Class)
	 * @see #getMappingForMethod(Method, Class)
	 * @see #handlerMethodsInitialized(Map)
	 */
	protected void initHandlerMethods() {
		if (logger.isDebugEnabled()) {
			logger.debug("Looking for request mappings in application context: " + getApplicationContext());
		}

		String[] beanNames = (this.detectHandlerMethodsInAncestorContexts ?
				BeanFactoryUtils.beanNamesForTypeIncludingAncestors(getApplicationContext(), Object.class) :
				getApplicationContext().getBeanNamesForType(Object.class));

		for (String beanName : beanNames) {
			if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX) &&
					isHandler(getApplicationContext().getType(beanName))){
				detectHandlerMethods(beanName);
			}
		}
		handlerMethodsInitialized(getHandlerMethods());
	}

其中的isHandler的判断方法代码如下：

/**
	 * {@inheritDoc}
	 * Expects a handler to have a type-level @{@link Controller} annotation.
	 */
	@Override
	protected boolean isHandler(Class<?> beanType) {
		return ((AnnotationUtils.findAnnotation(beanType, Controller.class) != null) ||
				(AnnotationUtils.findAnnotation(beanType, RequestMapping.class) != null));
	}

如果handler含有了上述注解的其中之一，就会进一步处理该handler的方法中含有@RequestMapping的方法：

/**
	 * Look for handler methods in a handler.
	 * @param handler the bean name of a handler or a handler instance
	 */
	protected void detectHandlerMethods(final Object handler) {
		Class<?> handlerType =
				(handler instanceof String ? getApplicationContext().getType((String) handler) : handler.getClass());

		// Avoid repeated calls to getMappingForMethod which would rebuild RequestMappingInfo instances
		final Map<Method, T> mappings = new IdentityHashMap<Method, T>();
		final Class<?> userType = ClassUtils.getUserClass(handlerType);

		Set<Method> methods = HandlerMethodSelector.selectMethods(userType, new MethodFilter() {
			@Override
			public boolean matches(Method method) {
				T mapping = getMappingForMethod(method, userType);
				if (mapping != null) {
					mappings.put(method, mapping);
					return true;
				}
				else {
					return false;
				}
			}
		});

		for (Method method : methods) {
			registerHandlerMethod(handler, method, mappings.get(method));
		}
	}

遍历这个handler类的所有方法，过滤条件就是这个内部类MethodFilter，其中的getMappingForMethod方法内容为：

/**
	 * Uses method and type-level @{@link RequestMapping} annotations to create
	 * the RequestMappingInfo.
	 * @return the created RequestMappingInfo, or {@code null} if the method
	 * does not have a {@code @RequestMapping} annotation.
	 * @see #getCustomMethodCondition(Method)
	 * @see #getCustomTypeCondition(Class)
	 */
	@Override
	protected RequestMappingInfo getMappingForMethod(Method method, Class<?> handlerType) {
		RequestMappingInfo info = null;
		RequestMapping methodAnnotation = AnnotationUtils.findAnnotation(method, RequestMapping.class);
		if (methodAnnotation != null) {
			RequestCondition<?> methodCondition = getCustomMethodCondition(method);
			info = createRequestMappingInfo(methodAnnotation, methodCondition);
			RequestMapping typeAnnotation = AnnotationUtils.findAnnotation(handlerType, RequestMapping.class);
			if (typeAnnotation != null) {
				RequestCondition<?> typeCondition = getCustomTypeCondition(handlerType);
				info = createRequestMappingInfo(typeAnnotation, typeCondition).combine(info);
			}
		}
		return info;
	}

如找到了含有RequestMapping注释的方法，则由这个注释的内容构建一个RequestMappingInfo对象：

/**
	 * Created a RequestMappingInfo from a RequestMapping annotation.
	 */
	protected RequestMappingInfo createRequestMappingInfo(RequestMapping annotation, RequestCondition<?> customCondition) {
		String[] patterns = resolveEmbeddedValuesInPatterns(annotation.value());
		return new RequestMappingInfo(
				new PatternsRequestCondition(patterns, getUrlPathHelper(), getPathMatcher(),
						this.useSuffixPatternMatch, this.useTrailingSlashMatch, this.fileExtensions),
				new RequestMethodsRequestCondition(annotation.method()),
				new ParamsRequestCondition(annotation.params()),
				new HeadersRequestCondition(annotation.headers()),
				new ConsumesRequestCondition(annotation.consumes(), annotation.headers()),
				new ProducesRequestCondition(annotation.produces(), annotation.headers(), this.contentNegotiationManager),
				customCondition);
	}

就是拿RequestMapping注释的内容进一步封装进RequestMappingInfo对象中。对handler的所有方法过滤完成之后，就要遍历这些方法，以一定的方式存储起来。

/**
	 * Register a handler method and its unique mapping.
	 * @param handler the bean name of the handler or the handler instance
	 * @param method the method to register
	 * @param mapping the mapping conditions associated with the handler method
	 * @throws IllegalStateException if another method was already registered
	 * under the same mapping
	 */
	protected void registerHandlerMethod(Object handler, Method method, T mapping) {
		HandlerMethod newHandlerMethod = createHandlerMethod(handler, method);
		HandlerMethod oldHandlerMethod = this.handlerMethods.get(mapping);
		if (oldHandlerMethod != null && !oldHandlerMethod.equals(newHandlerMethod)) {
			throw new IllegalStateException("Ambiguous mapping found. Cannot map '" + newHandlerMethod.getBean() +
					"' bean method \n" + newHandlerMethod + "\nto " + mapping + ": There is already '" +
					oldHandlerMethod.getBean() + "' bean method\n" + oldHandlerMethod + " mapped.");
		}

		this.handlerMethods.put(mapping, newHandlerMethod);
		if (logger.isInfoEnabled()) {
			logger.info("Mapped \"" + mapping + "\" onto " + newHandlerMethod);
		}

		Set<String> patterns = getMappingPathPatterns(mapping);
		for (String pattern : patterns) {
			if (!getPathMatcher().isPattern(pattern)) {
				this.urlMap.add(pattern, mapping);
			}
		}
	}

这里的this.handlerMethods就包含了所有管辖的bean，key为RequestMappingInfo对象，value为handler和它中含有@RequestMapping注释的方法method构建的HandlerMethod。
如下所示：

/**
	 * Create the HandlerMethod instance.
	 * @param handler either a bean name or an actual handler instance
	 * @param method the target method
	 * @return the created HandlerMethod
	 */
	protected HandlerMethod createHandlerMethod(Object handler, Method method) {
		HandlerMethod handlerMethod;
		if (handler instanceof String) {
			String beanName = (String) handler;
			handlerMethod = new HandlerMethod(beanName, getApplicationContext(), method);
		}
		else {
			handlerMethod = new HandlerMethod(handler, method);
		}
		return handlerMethod;
	}

至此，RequestMappingHandlerMapping的初始化注册工作就完成了。然后就是等待请求，访问
http://localhost:8080/string?name=aa，RequestMappingHandlerMapping会匹配到由StringAction对象和它的包含注释的方法testMessageConverter构建的HandlerMethod对象，该对象将作为handler，然后再遍历HandlerAdapter判断它们是否支持这个handler，RequestMappingHandlerAdapter的判断依据为是否是HandlerMethod 类型（在AbstractHandlerMethodAdapter类中）：

public final boolean supports(Object handler) {
		return handler instanceof HandlerMethod && supportsInternal((HandlerMethod) handler);
	}

然后将得到匹配，有了这个HandlerMethod对象，便可以通过RequestMappingHandlerAdapter来调度执行HandlerMethod其中的方法。