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

[size=medium]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[/size]

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

[size=medium]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:[/size]

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 } 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);

}


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

/**
* 这里清清楚楚写着该类是专门处理 标签的
* A {@link BeanDefinitionParser} that provides the configuration for the
* {@code } MVC namespace element.
*
* 这里说明了注册的HandlerMapping
*

This class registers the following {@link HandlerMapping}s:


*

    *
  • {@link RequestMappingHandlerMapping}
    * ordered at 0 for mapping requests to annotated controller methods.
    *
  • {@link BeanNameUrlHandlerMapping}
    * ordered at 2 to map URL paths to controller bean names.
    *

*
*

Note: Additional HandlerMappings may be registered
* as a result of using the {@code } or the
* {@code } MVC namespace elements.
*
* 这里说明了注册的HandlerAdapter
*

This class registers the following {@link HandlerAdapter}s:
*


    *
  • {@link RequestMappingHandlerAdapter}
    * for processing requests with annotated controller methods.
    *
  • {@link HttpRequestHandlerAdapter}
    * for processing requests with {@link HttpRequestHandler}s.
    *
  • {@link SimpleControllerHandlerAdapter}
    * for processing requests with interface-based {@link Controller}s.
    *

*
*

This class registers the following {@link HandlerExceptionResolver}s:
*


    *
  • {@link ExceptionHandlerExceptionResolver} for handling exceptions
    * through @{@link ExceptionHandler} methods.
    *
  • {@link ResponseStatusExceptionResolver} for exceptions annotated
    * with @{@link ResponseStatus}.
    *
  • {@link DefaultHandlerExceptionResolver} for resolving known Spring
    * exception types
    *

*
*

Both the {@link RequestMappingHandlerAdapter} and the
* {@link ExceptionHandlerExceptionResolver} are configured with instances of
* the following by default:
*


    *
  • A {@link ContentNegotiationManager}
    *
  • A {@link DefaultFormattingConversionService}
    *
  • A {@link org.springframework.validation.beanvalidation.LocalValidatorFactoryBean}
    * if a JSR-303 implementation is available on the classpath
    *
  • A range of {@link HttpMessageConverter}s depending on what 3rd party
    * libraries are available on the classpath.
    *

*
* @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
}

[size=medium]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:[/size]

@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;
}

[size=medium]MvcNamespaceUtils.registerDefaultComponents的内容如下:[/size]

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

[size=medium]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:[/size]

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


Archetype Created Web Application

mvc
org.springframework.web.servlet.DispatcherServlet
1



mvc
/*



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


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">













zh_CN












[size=medium]开启了,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[/size]

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;
}
}

[size=medium]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:
[/size]
[img]http://dl2.iteye.com/upload/attachment/0100/2900/49a4b62a-efdf-3256-8b29-7e8583eb396c.png[/img]
[size=medium]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:[/size]

/**
* 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());
}

[size=medium]其中的isHandler的判断方法代码如下:[/size]

/**
* {@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));
}

[size=medium]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:[/size]

/**
* 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 mappings = new IdentityHashMap();
final Class userType = ClassUtils.getUserClass(handlerType);

Set 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));
}
}

[size=medium]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:[/size]

/**
* 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;
}

[size=medium]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:[/size]

/**
* 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);
}

[size=medium]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。[/size]

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

[size=medium]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:[/size]

/**
* 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;
}

[size=medium]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):[/size]

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

[size=medium]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。[/size]

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