spring AOP实现原理，
spring 会在初始化的时候，创建一个BeanPostProcessor（AnnotationAwareAspectJAutoProxyCreator）用来为类注入切面。
AnnotationAwareAspectJAutoProxyCreator 是怎么加载到spring中的？
1. @EnableAutoConfiguration
2. AOPautoConfiguration
@Configuration
@ConditionalOnClass({ EnableAspectJAutoProxy.class, Aspect.class, Advice.class,
AnnotatedElement.class })
@ConditionalOnProperty(prefix = "spring.aop", name = "auto", havingValue = "true", matchIfMissing = true)
public class AopAutoConfiguration { @Configuration
@EnableAspectJAutoProxy(proxyTargetClass = false)
@ConditionalOnProperty(prefix = "spring.aop", name = "proxy-target-class", havingValue = "false", matchIfMissing = false)
public static class JdkDynamicAutoProxyConfiguration { } @Configuration
@EnableAspectJAutoProxy(proxyTargetClass = true)
@ConditionalOnProperty(prefix = "spring.aop", name = "proxy-target-class", havingValue = "true", matchIfMissing = true)
public static class CglibAutoProxyConfiguration { } }
3. 注入的过程
@Nullable
public static BeanDefinition registerAspectJAnnotationAutoProxyCreatorIfNecessary(BeanDefinitionRegistry registry) {
return registerAspectJAnnotationAutoProxyCreatorIfNecessary(registry, null);
} @Nullable
public static BeanDefinition registerAspectJAnnotationAutoProxyCreatorIfNecessary(BeanDefinitionRegistry registry,
@Nullable Object source) { return registerOrEscalateApcAsRequired(AnnotationAwareAspectJAutoProxyCreator.class, registry, source);
}
这个类的作用：
1.拦截 advisor 类。（建议类，为bean加载切面：包括自定的advisor,和transactionAdvisor）
AbstractAutoProxyCreator.java
public Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {
Object cacheKey = getCacheKey(beanClass, beanName);
if (!StringUtils.hasLength(beanName) || !this.targetSourcedBeans.contains(beanName)) {
if (this.advisedBeans.containsKey(cacheKey)) {
return null;
}
if (isInfrastructureClass(beanClass) || shouldSkip(beanClass, beanName)) {
this.advisedBeans.put(cacheKey, Boolean.FALSE);
return null;
}
}2.拦截带有切面注解的类，和切面定义拦截的类。
public Object postProcessAfterInitialization(@Nullable 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 (StringUtils.hasLength(beanName) && 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;
}
// Create proxy if we have advice.
Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
if (specificInterceptors != DO_NOT_PROXY) {
this.advisedBeans.put(cacheKey, Boolean.TRUE);
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;
}3.创建代理类
3.1根据proxyFactory 获取对应的代理类
public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
if (config.isOptimize() || config.isProxyTargetClass() || hasNoUserSuppliedProxyInterfaces(config)) {
Class<?> targetClass = config.getTargetClass();
if (targetClass == null) {
throw new AopConfigException("TargetSource cannot determine target class: " +
"Either an interface or a target is required for proxy creation.");
}
if (targetClass.isInterface() || Proxy.isProxyClass(targetClass)) {
return new JdkDynamicAopProxy(config);
}
return new ObjenesisCglibAopProxy(config);
}
else {
return new JdkDynamicAopProxy(config);
}
}3.2 使用proxy类，创建 proxyObject (和cglib的用法基本一样。)
enhancer.setSuperclass(proxySuperClass);
enhancer.setInterfaces(AopProxyUtils.completeProxiedInterfaces(this.advised));
enhancer.setNamingPolicy(SpringNamingPolicy.INSTANCE);
enhancer.setStrategy(new ClassLoaderAwareUndeclaredThrowableStrategy(classLoader)); Callback[] callbacks = getCallbacks(rootClass);
Class<?>[] types = new Class<?>[callbacks.length];
for (int x = 0; x < types.length; x++) {
types[x] = callbacks[x].getClass();
}
// fixedInterceptorMap only populated at this point, after getCallbacks call above
enhancer.setCallbackFilter(new ProxyCallbackFilter(
this.advised.getConfigurationOnlyCopy(), this.fixedInterceptorMap, this.fixedInterceptorOffset));
enhancer.setCallbackTypes(types); // Generate the proxy class and create a proxy instance.
return createProxyClassAndInstance(enhancer, callbacks);
4.targetSource 的作用和原理
targetSource 是一个 被代理的对象，用来封装具体的代理对象。所有生成后的代理对象，1.调用切面,2调用targetSource.getTarget()，3.会调用method.Invoke(target,args)
用处：
1.热交换 JndiObjectTargetSource 加载spring时，tomcat先加载了dataSource，此时对已有的dataSource加切面是不和实际的。所以可以对JNDIdatasource加切面，在调用具体的方法时，由targetSource交换的通过jndi查找到的数据源。
为了兼容targetSource有了
SingletonTargetSource，EmptyTargetSource，