spring在解析xml配置文件的时候，会根据传入的namespaceUri找到对应的NamespaceHandler，这个映射是在spring.handlers中配置的。
拿aop举例：
spring aop的配置文件肯定是要加这么一段aop的命名空间xmlns:aop=”http://www.springframework.org/schema/aop”
我们在spring-aop的META-INF/spring.handlers文件中找到了对应的namespaceHandler
http\://www.springframework.org/schema/aop=org.springframework.aop.config.AopNamespaceHandler下面就是看AopNamespaceHandler如何处理aop标签了。
public class AopNamespaceHandler extends NamespaceHandlerSupport {
/** * Register the {@link BeanDefinitionParser BeanDefinitionParsers} for the * '{@code config}', '{@code spring-configured}', '{@code aspectj-autoproxy}' * and '{@code scoped-proxy}' tags. */
@Override
public void init() {
// In 2.0 XSD as well as in 2.1 XSD.
registerBeanDefinitionParser("config", new ConfigBeanDefinitionParser());
registerBeanDefinitionParser("aspectj-autoproxy", new AspectJAutoProxyBeanDefinitionParser());
registerBeanDefinitionDecorator("scoped-proxy", new ScopedProxyBeanDefinitionDecorator());
// Only in 2.0 XSD: moved to context namespace as of 2.1
registerBeanDefinitionParser("spring-configured", new SpringConfiguredBeanDefinitionParser());
}
}
看一下AspectJAutoProxyBeanDefinitionParser的内部实现
@Override
public BeanDefinition parse(Element element, ParserContext parserContext) {
AopNamespaceUtils.registerAspectJAnnotationAutoProxyCreatorIfNecessary(parserContext, element);
extendBeanDefinition(element, parserContext);
return null;
}public static void registerAspectJAnnotationAutoProxyCreatorIfNecessary(
ParserContext parserContext, Element sourceElement) {
//注册或升级AutoProxyCreator定义beanName为org.springframework.aop.config.internalAutoProxyCreator的BeanDefinition
BeanDefinition beanDefinition = AopConfigUtils.registerAspectJAnnotationAutoProxyCreatorIfNecessary(
parserContext.getRegistry(), parserContext.extractSource(sourceElement));
//对于proxy-target-class以及expose-proxy属性的处理
useClassProxyingIfNecessary(parserContext.getRegistry(), sourceElement);
//注册组件并通知，便于监听器进一步处理
//其中beanDefinition的className为AnnotationAwareAspectJAutoProxyCreator
registerComponentIfNecessary(beanDefinition, parserContext);
}
public static BeanDefinition registerAspectJAnnotationAutoProxyCreatorIfNecessary(BeanDefinitionRegistry registry, Object source) {
return registerOrEscalateApcAsRequired(AnnotationAwareAspectJAutoProxyCreator.class, registry, source);
}
通过自定义配置完成对AnnotationAwareAspectJAutoProxyCreator类型的自动注册。
AnnotationAwareAspectJAutoProxyCreator 实现了BeanPostProcessor接口，当spring加载这个bean的时候会在实例化前调用postProcessAfterInitialization方法。aop的大门就此打开了
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
if (bean != null) {
Object cacheKey = getCacheKey(bean.getClass(), beanName);
if (!this.earlyProxyReferences.contains(cacheKey)) {
return wrapIfNecessary(bean, beanName, cacheKey);
}
}
return bean;
}protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
if (beanName != null && this.targetSourcedBeans.contains(beanName)) {
return bean;
}
if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {
return bean;
}
if (isInfrastructureClass(bean.getClass()) || shouldSkip(bean.getClass(), beanName)) {
this.advisedBeans.put(cacheKey, Boolean.FALSE);
return bean;
}
//如果存在增强方法则创建代理
Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
//如果获取到了增强需要针对增强创建代理
if (specificInterceptors != DO_NOT_PROXY) {
this.advisedBeans.put(cacheKey, Boolean.TRUE);
//创建代理
Object proxy = createProxy(bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
this.proxyTypes.put(cacheKey, proxy.getClass());
return proxy;
}
this.advisedBeans.put(cacheKey, Boolean.FALSE);
return bean;
}获取增强方法的实现：
@Override
protected Object[] getAdvicesAndAdvisorsForBean(Class<?> beanClass, String beanName, TargetSource targetSource) {
List<Advisor> advisors = findEligibleAdvisors(beanClass, beanName);
if (advisors.isEmpty()) {
return DO_NOT_PROXY;
}
return advisors.toArray();
}protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {
List<Advisor> candidateAdvisors = findCandidateAdvisors();//获取所有的增强
List<Advisor> eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);
//从所有增强中寻找适合该bean的增强并且应用
extendAdvisors(eligibleAdvisors);
if (!eligibleAdvisors.isEmpty()) {
eligibleAdvisors = sortAdvisors(eligibleAdvisors);
}
return eligibleAdvisors;
}@Override
protected List<Advisor> findCandidateAdvisors() {
// Add all the Spring advisors found according to superclass rules.
List<Advisor> advisors = super.findCandidateAdvisors();
// Build Advisors for all AspectJ aspects in the bean factory.
advisors.addAll(this.aspectJAdvisorsBuilder.buildAspectJAdvisors());
return advisors;
}public List<Advisor> buildAspectJAdvisors() {
List<String> aspectNames = null;
synchronized (this) {
aspectNames = this.aspectBeanNames;
if (aspectNames == null) {
List<Advisor> advisors = new LinkedList<>();
aspectNames = new LinkedList<>();
//获取所有的beanName
String[] beanNames＝BeanFactoryUtils.beanNamesForTypeIncludingAncestors(this.beanFactory, Object.class, true, false);
//循环所有beanName找出对应的增强方法
for (String beanName : beanNames) {
if (!isEligibleBean(beanName)) {
continue;
}
// We must be careful not to instantiate beans eagerly as in this
// case they would be cached by the Spring container but would not
// have been weaved
Class<?> beanType = this.beanFactory.getType(beanName);
if (beanType == null) {
continue;
}
//如果存在Aspect注解
if (this.advisorFactory.isAspect(beanType)) {
aspectNames.add(beanName);
AspectMetadata amd = new AspectMetadata(beanType, beanName);
if (amd.getAjType().getPerClause().getKind() == PerClauseKind.SINGLETON) {
MetadataAwareAspectInstanceFactory factory =
new BeanFactoryAspectInstanceFactory(this.beanFactory, beanName);
//解析标记AspectJ注解额增强方法
List<Advisor> classAdvisors = this.advisorFactory.getAdvisors(factory);
if (this.beanFactory.isSingleton(beanName)) {
this.advisorsCache.put(beanName, classAdvisors);
}
else {
this.aspectFactoryCache.put(beanName, factory);
}
advisors.addAll(classAdvisors);
}
else {
// Per target or per this.
if (this.beanFactory.isSingleton(beanName)) {
throw new IllegalArgumentException("Bean with name '" + beanName +
"' is a singleton, but aspect instantiation model is not singleton");
}
MetadataAwareAspectInstanceFactory factory =
new PrototypeAspectInstanceFactory(this.beanFactory, beanName);
this.aspectFactoryCache.put(beanName, factory);
advisors.addAll(this.advisorFactory.getAdvisors(factory));
}
}
}
this.aspectBeanNames = aspectNames;
return advisors;
}
}
if (aspectNames.isEmpty()) {
return Collections.emptyList();
}
List<Advisor> advisors = new LinkedList<>();
for (String aspectName : aspectNames) {
List<Advisor> cachedAdvisors = this.advisorsCache.get(aspectName);
if (cachedAdvisors != null) {
advisors.addAll(cachedAdvisors);
}
else {
MetadataAwareAspectInstanceFactory factory = this.aspectFactoryCache.get(aspectName);
advisors.addAll(this.advisorFactory.getAdvisors(factory));
}
}
return advisors;
}下一篇了解getAdvisors方法是如何实现增强器的获取的
