本文章接上一篇，上一票最后介绍了getAdvisor的作用，
1.获取 AspectJ 表达式切点，
2.创建 Advisor 实现类
Advisor 实现类的创建过程
public InstantiationModelAwarePointcutAdvisorImpl(AspectJExpressionPointcut declaredPointcut,
Method aspectJAdviceMethod, AspectJAdvisorFactory aspectJAdvisorFactory,
MetadataAwareAspectInstanceFactory aspectInstanceFactory, int declarationOrder, String aspectName) {
this.declaredPointcut = declaredPointcut;
this.declaringClass = aspectJAdviceMethod.getDeclaringClass();
this.methodName = aspectJAdviceMethod.getName();
this.parameterTypes = aspectJAdviceMethod.getParameterTypes();
this.aspectJAdviceMethod = aspectJAdviceMethod;
this.aspectJAdvisorFactory = aspectJAdvisorFactory;
this.aspectInstanceFactory = aspectInstanceFactory;
this.declarationOrder = declarationOrder;
this.aspectName = aspectName;
if (aspectInstanceFactory.getAspectMetadata().isLazilyInstantiated()) {
Pointcut preInstantiationPointcut = Pointcuts.union(
aspectInstanceFactory.getAspectMetadata().getPerClausePointcut(), this.declaredPointcut);
this.pointcut = new PerTargetInstantiationModelPointcut(
this.declaredPointcut, preInstantiationPointcut, aspectInstanceFactory);
this.lazy = true;
}
else {
this.pointcut = this.declaredPointcut;
this.lazy = false;
// 按照注解解析 Advice
this.instantiatedAdvice = instantiateAdvice(this.declaredPointcut);
}
}
instantiateAdvice(this.declaredPointcut)，
这个方法用于创建通知 Advice,具体如下
private Advice instantiateAdvice(AspectJExpressionPointcut pcut) {
return this.aspectJAdvisorFactory.getAdvice(this.aspectJAdviceMethod, pcut,
this.aspectInstanceFactory, this.declarationOrder, this.aspectName);
}
public Advice getAdvice(Method candidateAdviceMethod, AspectJExpressionPointcut expressionPointcut,
MetadataAwareAspectInstanceFactory aspectInstanceFactory, int declarationOrder, String aspectName) {
Class candidateAspectClass = aspectInstanceFactory.getAspectMetadata().getAspectClass();
validate(candidateAspectClass);
// 获取 Advice 注解
AspectJAnnotation aspectJAnnotation =
AbstractAspectJAdvisorFactory.findAspectJAnnotationOnMethod(candidateAdviceMethod);
if (aspectJAnnotation == null) {
return null;
}
if (!isAspect(candidateAspectClass)) {
throw new AopConfigException("Advice must be declared inside an aspect type: " +
"Offending method '" + candidateAdviceMethod + "' in class [" +
candidateAspectClass.getName() + "]");
}
if (logger.isDebugEnabled()) {
logger.debug("Found AspectJ method: " + candidateAdviceMethod);
}
AbstractAspectJAdvice springAdvice;
// 按照注解类型生成相应的 Advice 实现类
switch (aspectJAnnotation.getAnnotationType()) {
case AtBefore: // @Before -> AspectJMethodBeforeAdvice
springAdvice = new AspectJMethodBeforeAdvice(
candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
break;
case AtAfter: // @After -> AspectJAfterAdvice
springAdvice = new AspectJAfterAdvice(
candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
break;
case AtAfterReturning: // @AfterReturning -> AspectJAfterAdvice
springAdvice = new AspectJAfterReturningAdvice(
candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
AfterReturning afterReturningAnnotation = (AfterReturning) aspectJAnnotation.getAnnotation();
if (StringUtils.hasText(afterReturningAnnotation.returning())) {
springAdvice.setReturningName(afterReturningAnnotation.returning());
}
break;
case AtAfterThrowing: // @AfterThrowing -> AspectJAfterThrowingAdvice
springAdvice = new AspectJAfterThrowingAdvice(
candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
AfterThrowing afterThrowingAnnotation = (AfterThrowing) aspectJAnnotation.getAnnotation();
if (StringUtils.hasText(afterThrowingAnnotation.throwing())) {
springAdvice.setThrowingName(afterThrowingAnnotation.throwing());
}
break;
case AtAround: // @Around -> AspectJAroundAdvice
springAdvice = new AspectJAroundAdvice(
candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
break;
/*
* 什么都不做，直接返回 null。从整个方法的调用栈来看，
* 并不会出现注解类型为 AtPointcut 的情况
*/
case AtPointcut:
if (logger.isDebugEnabled()) {
logger.debug("Processing pointcut '" + candidateAdviceMethod.getName() + "'");
}
return null;
default:
throw new UnsupportedOperationException(
"Unsupported advice type on method: " + candidateAdviceMethod);
}
springAdvice.setAspectName(aspectName);
springAdvice.setDeclarationOrder(declarationOrder);
/*
* 获取方法的参数列表名称，比如方法 int sum(int numX, int numY),
* getParameterNames(sum) 得到 argNames = [numX, numY]
*/
String[] argNames = this.parameterNameDiscoverer.getParameterNames(candidateAdviceMethod);
if (argNames != null) {
// 设置参数名
springAdvice.setArgumentNamesFromStringArray(argNames);
}
springAdvice.calculateArgumentBindings();
return springAdvice;
}
主要的逻辑就是根据注解类型生成与之对应的通知对象。
获取通知器（getAdvisors）整个过程的逻辑，如下：
1.从目标 bean 中获取不包含 Pointcut 注解的方法列表
2.遍历上一步获取的方法列表，并调用 getAdvisor 获取当前方法对应的 Advisor
3创建 AspectJExpressionPointcut 对象，并从方法中的注解中获取表达式，最后设置到切点对象中
4.创建 Advisor 实现类对象 InstantiationModelAwarePointcutAdvisorImpl
5.调用 instantiateAdvice 方法构建通知
6.调用 getAdvice 方法，并根据注解类型创建相应的通知。
AspectJMethodBeforeAdvice，
也就是 @Before 注解对应的通知实现类。
public class AspectJMethodBeforeAdvice extends AbstractAspectJAdvice implements MethodBeforeAdvice {
public AspectJMethodBeforeAdvice(
Method aspectJBeforeAdviceMethod, AspectJExpressionPointcut pointcut, AspectInstanceFactory aif) {
super(aspectJBeforeAdviceMethod, pointcut, aif);
}
@Override
public void before(Method method, Object[] args, Object target) throws Throwable {
// 调用通知方法
invokeAdviceMethod(getJoinPointMatch(), null, null);
}
@Override
public boolean isBeforeAdvice() {
return true;
}
@Override
public boolean isAfterAdvice() {
return false;
}
}
protected Object invokeAdviceMethod(JoinPointMatch jpMatch, Object returnValue, Throwable ex) throws Throwable {
// 调用通知方法，并向其传递参数
return invokeAdviceMethodWithGivenArgs(argBinding(getJoinPoint(), jpMatch, returnValue, ex));
}
protected Object invokeAdviceMethodWithGivenArgs(Object[] args) throws Throwable {
Object[] actualArgs = args;
if (this.aspectJAdviceMethod.getParameterTypes().length == 0) {
actualArgs = null;
}
try {
ReflectionUtils.makeAccessible(this.aspectJAdviceMethod);
// 通过反射调用通知方法
return this.aspectJAdviceMethod.invoke(this.aspectInstanceFactory.getAspectInstance(), actualArgs);
}
catch (IllegalArgumentException ex) {
throw new AopInvocationException("Mismatch on arguments to advice method [" +
this.aspectJAdviceMethod + "]; pointcut expression [" +
this.pointcut.getPointcutExpression() + "]", ex);
}
catch (InvocationTargetException ex) {
throw ex.getTargetException();
}
}
以上描述了如何为目标 bean 筛选合适的通知器的，下面介绍了
创建代理对象
proxy-target-class的配置
Spring AOP 配置中，proxy-target-class 属性可影响 Spring 生成的代理对象的类型。以 XML 配置为例，默认情况下 proxy-target-class 属性为 false。当目标 bean 实现了接口时，Spring 会基于 JDK 动态代理为目标 bean 创建代理对象。若未实现任何接口，Spring 则会通过 CGLIB 创建代理。而当 proxy-target-class 属性设为 true 时，则会强制 Spring 通过 CGLIB 的方式创建代理对象，即使目标 bean 实现了接口。
动态代理的两种
1。基于 JDK 的动态代理（之前文章已经提过）
2。基于 CGLIB 的动态代理（不需要实现接口生成，后续专题再介绍）
源码分析
public interface AopProxy {
/** 创建代理对象 */
Object getProxy();
Object getProxy(ClassLoader classLoader);
}
在 Spring 中，有两个类实现了 AopProxy
1.ObjenesisCglibAopProxy 继承CglibAopProxy（实现了AopProxy接口）
2.JdkDynamicAopProxy（实现了AopProxy接口）
创建代理的过程
protected Object createProxy(
Class beanClass, String beanName, Object[] specificInterceptors, TargetSource targetSource) {
if (this.beanFactory instanceof ConfigurableListableBeanFactory) {
AutoProxyUtils.exposeTargetClass((ConfigurableListableBeanFactory) this.beanFactory, beanName, beanClass);
}
ProxyFactory proxyFactory = new ProxyFactory();
proxyFactory.copyFrom(this);
/*
* 默认配置下，或用户显式配置 proxy-target-class = "false" 时，
* 这里的 proxyFactory.isProxyTargetClass() 也为 false
*/
if (!proxyFactory.isProxyTargetClass()) {
if (shouldProxyTargetClass(beanClass, beanName)) {
proxyFactory.setProxyTargetClass(true);
}
else {
/*
* 检测 beanClass 是否实现了接口，若未实现，则将
* proxyFactory 的成员变量 proxyTargetClass 设为 true
*/
evaluateProxyInterfaces(beanClass, proxyFactory);
}
}
// specificInterceptors 中若包含有 Advice，此处将 Advice 转为 Advisor
Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);
proxyFactory.addAdvisors(advisors);
proxyFactory.setTargetSource(targetSource);
customizeProxyFactory(proxyFactory);
proxyFactory.setFrozen(this.freezeProxy);
if (advisorsPreFiltered()) {
proxyFactory.setPreFiltered(true);
}
// 创建代理
return proxyFactory.getProxy(getProxyClassLoader());
}
public Object getProxy(ClassLoader classLoader) {
// 先创建 AopProxy 实现类对象，然后再调用 getProxy 为目标 bean 创建代理对象
return createAopProxy().getProxy(classLoader);
}
getProxy 这里有两个方法调用，
1.调用 createAopProxy 创建 AopProxy 实现类对象，
2.调用 AopProxy 实现类对象中的 getProxy 创建代理对象。
创建 AopProxy 实现类对象的过程
protected final synchronized AopProxy createAopProxy() {
if (!this.active) {
activate();
}
return getAopProxyFactory().createAopProxy(this);
}
public class DefaultAopProxyFactory implements AopProxyFactory, Serializable {
@Override
public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
/*
* 下面的三个条件简单分析一下：
*
* 条件1：config.isOptimize() - isOptimize表示让spring自行优化，默认为false
* 细节我不是很清楚
* 条件2：config.isProxyTargetClass() - 检测 proxyTargetClass 的值，
* 前面的代码会设置这个值
* 条件3：hasNoUserSuppliedProxyInterfaces(config)
* - 目标 bean 是否实现了接口
*/
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);
}
// 创建 CGLIB 代理，ObjenesisCglibAopProxy 继承自 CglibAopProxy
return new ObjenesisCglibAopProxy(config);
}
else {
// 创建 JDK 动态代理
return new JdkDynamicAopProxy(config);
DefaultAopProxyFactory 根据一些条件决定生成什么类型的 AopProxy 实现类对象。生成好 AopProxy 实现类对象后，下面就要为目标 bean 创建代理对象了。
JdkDynamicAopProxy为例
public Object getProxy() {
return getProxy(ClassUtils.getDefaultClassLoader());
}
public Object getProxy(ClassLoader classLoader) {
if (logger.isDebugEnabled()) {
logger.debug("Creating JDK dynamic proxy: target source is " + this.advised.getTargetSource());
}
Class[] proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised, true);
findDefinedEqualsAndHashCodeMethods(proxiedInterfaces);
// 调用 newProxyInstance 创建代理对象
return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
}
会发现 JdkDynamicAopProxy 最终调用 Proxy.newProxyInstance 方法创建代理对象