SpringMVC源码总结（二）mvc:annotation 博客分类： Spring框架

程序员文章站 2024-03-24 19:41:58

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SpringMVC源码总结（二）mvc:annotation

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

Java代码

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：

Java代码

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}.
* 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 not 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：

Java代码

/**
* 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
* This class registers the following {@link HandlerMapping}s:
* <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>
*
* Note: 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
* 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>
*
* 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>
*
* 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：

Java代码

@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：

Java代码

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：

Java代码

<!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：

Java代码

<?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

Java代码

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：

SpringMVC源码总结（二）mvc:annotation

博客分类： Spring框架

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：

Java代码

/**
* 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：

Java代码

/**
* {@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：

Java代码

/**
* 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：

Java代码

/**
* 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：

Java代码

/**
* 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。

Java代码

/**
* 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：

Java代码

/**
* 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）：

Java代码

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

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