spring aop 初探

org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator#wrapIfNecessary

分析JDK动态代理

生成的代理对象构造函数，入参为 InvocationHandler

public com.sun.proxy.$Proxy164(java.lang.reflect.InvocationHandler)

生成动态代理Class对象：

Class<?> cl = getProxyClass0(loader, intfs);

实例化动态代理对象：

final Constructor<?> cons = cl.getConstructor({ InvocationHandler.class });

cons.newInstance(new Object[]{h});

方法

equals,toString,hashCode

0 = {Method@10598} "public final boolean com.sun.proxy.$Proxy164.equals(java.lang.Object)"
1 = {Method@10599} "public final java.lang.String com.sun.proxy.$Proxy164.toString()"
2 = {Method@10600} "public final int com.sun.proxy.$Proxy164.hashCode()"

和所有代理接口中的所有方法。

代理对象的方法实现逻辑：比如 equals方法

return ((Boolean)this.h.invoke(this, m1, new Object[] { paramObject })).booleanValue();

就是调用

java.lang.reflect.InvocationHandler#invoke

public interface InvocationHandler {

    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable;

}

第一个参数，代理对象本身

第二个参数，调用的代理的接口中的方法

第三个参数，调用的方法入参

JDK动态代理需要开发者关注的，就是实现 InvocationHandler 接口。实际也并不需要很复杂的实现，可以引用另一个服务来实现。

org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator

在spring 实例化 bean之后，会执行

public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) {
		if (bean != null) {
			Object cacheKey = getCacheKey(bean.getClass(), beanName);
			if (this.earlyProxyReferences.remove(cacheKey) != bean) {
				return wrapIfNecessary(bean, beanName, cacheKey);
			}
		}
		return bean;
	}

完成aop 代理对象的生成。

JDK动态代理的 InvocationHandler 的实现类为 JdkDynamicAopProxy，其增强功能由 advised 完成。和上面画的结构基本一致。

Advisor

寻找Advisor

// org.springframework.aop.aspectj.annotation.AnnotationAwareAspectJAutoProxyCreator#findCandidateAdvisors
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.
		if (this.aspectJAdvisorsBuilder != null) {
			advisors.addAll(this.aspectJAdvisorsBuilder.buildAspectJAdvisors());
		}
		return advisors;
	}

第一部分，直接查找所有的 Advisor类型的bean

this.beanFactory.getBean(name, Advisor.class)

第二部分，查询标有 @Aspect 注解的 bean

private boolean hasAspectAnnotation(Class<?> clazz) {
		return (AnnotationUtils.findAnnotation(clazz, Aspect.class) != null);
	}

针对每个bean，找到所有没有标记 @Pointcut 注解的方法

对每个方法查找对应的切面，标记标记 @Around等注解的方法

private static final Class<?>[] ASPECTJ_ANNOTATION_CLASSES = new Class<?>[] {
			Pointcut.class, Around.class, Before.class, After.class, AfterReturning.class, AfterThrowing.class};

protected enum AspectJAnnotationType {

		AtPointcut, AtAround, AtBefore, AtAfter, AtAfterReturning, AtAfterThrowing
}

获取注解的value值，通常返回的是标记有 @Pointcut 注解的方法名

Method method = annotation.annotationType().getDeclaredMethod(attributeName);
ReflectionUtils.makeAccessible(method);
return method.invoke(annotation);

开始包装该切面方法：

关键代码块

switch (aspectJAnnotation.getAnnotationType()) {
			case AtPointcut:
				if (logger.isDebugEnabled()) {
					logger.debug("Processing pointcut '" + candidateAdviceMethod.getName() + "'");
				}
				return null;
			case AtAround:
				springAdvice = new AspectJAroundAdvice(
						candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
				break;
			case AtBefore:
				springAdvice = new AspectJMethodBeforeAdvice(
						candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
				break;
			case AtAfter:
				springAdvice = new AspectJAfterAdvice(
						candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
				break;
			case AtAfterReturning:
				springAdvice = new AspectJAfterReturningAdvice(
						candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
				AfterReturning afterReturningAnnotation = (AfterReturning) aspectJAnnotation.getAnnotation();
				if (StringUtils.hasText(afterReturningAnnotation.returning())) {
					springAdvice.setReturningName(afterReturningAnnotation.returning());
				}
				break;
			case AtAfterThrowing:
				springAdvice = new AspectJAfterThrowingAdvice(
						candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
				AfterThrowing afterThrowingAnnotation = (AfterThrowing) aspectJAnnotation.getAnnotation();
				if (StringUtils.hasText(afterThrowingAnnotation.throwing())) {
					springAdvice.setThrowingName(afterThrowingAnnotation.throwing());
				}
				break;
			default:
				throw new UnsupportedOperationException(
						"Unsupported advice type on method: " + candidateAdviceMethod);
		}

根据切面的类型，返回不同的Advice类型的对象。

寻找可以应用在当前bean的 advisor。这个逻辑有点复杂，先跳过

return canApply(pca.getPointcut(), targetClass, hasIntroductions);

接下来就是创建代理对象

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);
		}
	}

这边代码看起来绕来绕去，实际设计的比较精炼。使用一个工厂类的一个方法就返回了代理对象。

proxyFactory.getProxy(getProxyClassLoader());

createAopProxy().getProxy(classLoader)

getAopProxyFactory().createAopProxy(this)

多个方法级联调用，只是这里进行了一个拆分。

public JdkDynamicAopProxy(AdvisedSupport config) throws AopConfigException {
		Assert.notNull(config, "AdvisedSupport must not be null");
		if (config.getAdvisors().length == 0 && config.getTargetSource() == AdvisedSupport.EMPTY_TARGET_SOURCE) {
			throw new AopConfigException("No advisors and no TargetSource specified");
		}
		this.advised = config;
	}

上面描述了，JdkDynamicAopProxy就是 InvocationHandler的实现类。