Spring源码深度解析---创建AOP代理
前言
我们都知道要使用AOP需要自定义配置完成对AnnotationAwareAspectJAutoProxyCreator类型的自动注册。当Spring加载这个bean时会在实例化前调用其postProcessAfterInitialization方法，对于AOP逻辑的分析由此开始。
创建代理流程
在父类AbstractAutoProxyCreator的postProcessAfterInitialization方法
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
if (bean != null) {
// 首先根据bean的class和name构建出key
Object cacheKey = this.getCacheKey(bean.getClass(), beanName);
// 判断是否需要创建指定的bean
if (!this.earlyProxyReferences.contains(cacheKey)) {
//如果它适合被代理，则需要封装指定bean
return this.wrapIfNecessary(bean, beanName, cacheKey);
}
}
return bean;
}
protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
//如果已经处理过
if (beanName != null && this.targetSourcedBeans.contains(beanName)) {
return bean;
}
//无需增强
if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {
return bean;
}
//给定的bean类是否代表一个基础设施类，基本设施类不应代理，或配置类指定bean不需要自动代理
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);
//如果获得了增强则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;
}
从上面代码看出创建代理主要包含了两个步骤：
- 获取增强方法或增强器
- 根据获取的增强进行代理
获取增强方法
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) {
// 获取所有的增强
List<Advisor> candidateAdvisors = findCandidateAdvisors();
//寻找所有增强中适用于bean的增强并应用
List<Advisor> eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);
extendAdvisors(eligibleAdvisors);
if (!eligibleAdvisors.isEmpty()) {
eligibleAdvisors = sortAdvisors(eligibleAdvisors);
}
return eligibleAdvisors;
}
从上面代码看出获取增强方法主要包含了两个步骤：
- 获取所有的增强
- 寻找所有增强中适用于bean的增强并应用
获取增强器
继续跟踪到AnnotationAwareAspectJAutoProxyCreator的findCandidateAdvisors()方法
protected List<Advisor> findCandidateAdvisors() {
// 添加根据父类规则找到的所有Spring增强
List<Advisor> advisors = super.findCandidateAdvisors();
// 添加Bean注解增强的功能
advisors.addAll(this.aspectJAdvisorsBuilder.buildAspectJAdvisors());
return advisors;
}
public List<Advisor> buildAspectJAdvisors() {
List<String> aspectNames = this.aspectBeanNames;
if (aspectNames == null) {
synchronized (this) {
aspectNames = this.aspectBeanNames;
if (aspectNames == null) {
List<Advisor> advisors = new LinkedList<Advisor>();
aspectNames = new LinkedList<String>();
//获取所有beanName
String[] beanNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
this.beanFactory, Object.class, true, false);
//循环所有的beanName找出对应的增强方法
for (String beanName : beanNames) {
//不合法的bean则略过
if (!isEligibleBean(beanName)) {
continue;
}
//获取对应的bean的类型
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注解中的增强方法
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();
}
//记录在缓存中
List<Advisor> advisors = new LinkedList<Advisor>();
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;
}
从上面代码看出获取增强器主要步骤
- 获取所有beanName，这一步骤所有在beanFactory中注册的Bean都会被提取出来
- 遍历所有beanName，并找出声明AspectJ注解的类，进行进一步的处理
- 对标记为AspectJ注解的类进行增强器的提取
- 将提取结果加入缓存
增强器的获取这个功能委托给getAdvisors方法去实现
public List<Advisor> getAdvisors(MetadataAwareAspectInstanceFactory aspectInstanceFactory) {
//获取标记为AspectJ的类
Class<?> aspectClass = aspectInstanceFactory.getAspectMetadata().getAspectClass();
//获取标记为AspectJ的name
String aspectName = aspectInstanceFactory.getAspectMetadata().getAspectName();
//验证
validate(aspectClass);
// We need to wrap the MetadataAwareAspectInstanceFactory with a decorator
// so that it will only instantiate once.
MetadataAwareAspectInstanceFactory lazySingletonAspectInstanceFactory =
new LazySingletonAspectInstanceFactoryDecorator(aspectInstanceFactory);
List<Advisor> advisors = new LinkedList<Advisor>();
for (Method method : getAdvisorMethods(aspectClass)) {
Advisor advisor = getAdvisor(method, lazySingletonAspectInstanceFactory, advisors.size(), aspectName);
if (advisor != null) {
advisors.add(advisor);
}
}
// If it's a per target aspect, emit the dummy instantiating aspect.
if (!advisors.isEmpty() && lazySingletonAspectInstanceFactory.getAspectMetadata().isLazilyInstantiated()) {
//如果寻找的增强器不为空而且又配置了增强延迟初始化那么需要在首位加入同步实例化增强器
Advisor instantiationAdvisor = new SyntheticInstantiationAdvisor(lazySingletonAspectInstanceFactory);
advisors.add(0, instantiationAdvisor);
}
// Find introduction fields.
for (Field field : aspectClass.getDeclaredFields()) {
Advisor advisor = getDeclareParentsAdvisor(field);
if (advisor != null) {
advisors.add(advisor);
}
}
return advisors;
}
普通增强器的获取
普通增强器的获取逻辑通过getAdvisor方法实现
public Advisor getAdvisor(Method candidateAdviceMethod, MetadataAwareAspectInstanceFactory aspectInstanceFactory,
int declarationOrderInAspect, String aspectName) {
validate(aspectInstanceFactory.getAspectMetadata().getAspectClass());
//切点信息获取
AspectJExpressionPointcut expressionPointcut = getPointcut(
candidateAdviceMethod, aspectInstanceFactory.getAspectMetadata().getAspectClass());
if (expressionPointcut == null) {
return null;
}
//根据切点信息生成增强器
return new InstantiationModelAwarePointcutAdvisorImpl(expressionPointcut, candidateAdviceMethod,
this, aspectInstanceFactory, declarationOrderInAspect, aspectName);
}
实现步骤有两步
- 对切点的注解的获取
- 根据切点的注解生成增强
（1）切点信息获取，就是指定注解的表达式信息的获取，如@Before(“test”)
private AspectJExpressionPointcut getPointcut(Method candidateAdviceMethod, Class<?> candidateAspectClass) {
//获取方法上的注解
AspectJAnnotation<?> aspectJAnnotation =
AbstractAspectJAdvisorFactory.findAspectJAnnotationOnMethod(candidateAdviceMethod);
if (aspectJAnnotation == null) {
return null;
}
//使用AspectJExpressionPointcut实例封装获取的信息
AspectJExpressionPointcut ajexp =
new AspectJExpressionPointcut(candidateAspectClass, new String[0], new Class<?>[0]);
//提取得到的注解中的表达式
ajexp.setExpression(aspectJAnnotation.getPointcutExpression());
ajexp.setBeanFactory(this.beanFactory);
return ajexp;
}
（2）根据切点信息生成增强，由getAdvice（）方法实现
public Advice getAdvice(Method candidateAdviceMethod, AspectJExpressionPointcut expressionPointcut,
MetadataAwareAspectInstanceFactory aspectInstanceFactory, int declarationOrder, String aspectName) {
Class<?> candidateAspectClass = aspectInstanceFactory.getAspectMetadata().getAspectClass();
validate(candidateAspectClass);
AspectJAnnotation<?> aspectJAnnotation =
AbstractAspectJAdvisorFactory.findAspectJAnnotationOnMethod(candidateAdviceMethod);
if (aspectJAnnotation == null) {
return null;
}
// If we get here, we know we have an AspectJ method.
// Check that it's an AspectJ-annotated class
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;
//根据不同的注解类型封装不同的增强器
switch (aspectJAnnotation.getAnnotationType()) {
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;
case AtAround:
springAdvice = new AspectJAroundAdvice(
candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
break;
case AtPointcut:
if (logger.isDebugEnabled()) {
logger.debug("Processing pointcut '" + candidateAdviceMethod.getName() + "'");
}
return null;
default:
throw new UnsupportedOperationException(
"Unsupported advice type on method: " + candidateAdviceMethod);
}
// Now to configure the advice...
springAdvice.setAspectName(aspectName);
springAdvice.setDeclarationOrder(declarationOrder);
String[] argNames = this.parameterNameDiscoverer.getParameterNames(candidateAdviceMethod);
if (argNames != null) {
springAdvice.setArgumentNamesFromStringArray(argNames);
}
springAdvice.calculateArgumentBindings();
return springAdvice;
}
根据方法代码可以看出Spring根据不同的注解类型封装不同的增强器，比如AtBefore类型会生成AspectJMethodBeforeAdvice，AtAfter类型会生成AspectJAfterAdvice。
创建代理
在获取了所有对于bean的增强器后，便进行代理的创建了
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();
//获取当前类中相关属性
proxyFactory.copyFrom(this);
//决定对于给定的bean是否应该使用targetClass而不是他的接口代理
if (!proxyFactory.isProxyTargetClass()) {
if (shouldProxyTargetClass(beanClass, beanName)) {
proxyFactory.setProxyTargetClass(true);
}
else {
//添加接口代理
evaluateProxyInterfaces(beanClass, proxyFactory);
}
}
Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);
//加入增强器
proxyFactory.addAdvisors(advisors);
//设置要代理的类
proxyFactory.setTargetSource(targetSource);
//定制代理
customizeProxyFactory(proxyFactory);
//用来控制代理工厂被配置之后，是否还允许修改通知
proxyFactory.setFrozen(this.freezeProxy);
if (advisorsPreFiltered()) {
proxyFactory.setPreFiltered(true);
}
return proxyFactory.getProxy(getProxyClassLoader());
}
对于代理类的创建和处理，Spring委托给ProxyFactory处理，而且上面方法主要ProxyFactory的初始化操作，为真正的创建代理做准备，这些初始化步骤包括
- 获取当前类中相关属性
- 添加代理接口
- 封装Advisor并加入ProxyFactory
- 设置要代理的类
- 定制代理
- 进行获取代理操作
1、创建代理
Spring的代理有分JDK动态代理的实现和CGLIB代理的实现
Spring是如何选择使用哪个代理方式实现AOP呢
- 如果目标对象实现了接口，默认情况会使用JDK的接口代理实现AOP
- 如果目标对象实现了接口，可以强制使用CGLIB实现AOP
- 如果目标对象没有实现了接口，必须采用CGLIB库（CGLIB底层可以通过字节码生成代理对象的子类，通过子类对代理对象进行代理）
Spring会自动在JDK动态代理和CGLIB之间转换
1、JDK动态代理
JDK代理示例
创建业务接口
public interface UserService {
/**
* 目标方法
*/
public abstract void add();
}
创建业务接口实现类
public class UserServiceImpl implements UserService {
@Override
public void add() {
System.out.println("--------add-----------");
}
}
创建自定义InvocationHandle，用于对接口提供的方法进行增强
public class MyInvocationHandler implements InvocationHandler {
//目标对象
private Object target;
public MyInvocationHandler(Object target) {
super();
this.target = target;
}
//执行目标对象的方法
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
System.out.println("--------before----------");
//执行目标对象的方法
Object result = method.invoke(target, args);
System.out.println("---------after-----------");
return result;
}
//获取目标对象的代理对象
public Object getProxy() {
return Proxy.newProxyInstance(Thread.currentThread().getContextClassLoader(),
target.getClass().getInterfaces(), this);
}
}
测试
public class ProxyTest {
public static void main(String[] args) {
UserServiceImpl userService = new UserServiceImpl();
MyInvocationHandler myInvocationHandler = new MyInvocationHandler(userService);
UserService proxy = (UserService) myInvocationHandler.getProxy();
proxy.add();
}
}
上面示例基本上是AOP的一个基本实现，在目标对象的方法执行前后进行了增强，Spring的AOP实现其实也是用了Proxy和InvocationHandler这两个东西。
在自定义的InvocationHandler中需要重写3个方法
- 构造方法，将代理的对象传入
- invoke方法，此方法中实现了AOP增强的所有逻辑
- getProxy方法
在Spring中的JdkDynamicAopProxy也是实现InvocationHandler接口，JdkDynamicAopProxy同样把AOP的核心逻辑写在invoke方法
 throws Throwable {
MethodInvocation invocation;
Object oldProxy = null;
boolean setProxyContext = false;
TargetSource targetSource = this.advised.targetSource;
Class<?> targetClass = null;
Object target = null;
try {
if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) {
// The target does not implement the equals(Object) method itself.
return equals(args[0]);
}
else if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)) {
// The target does not implement the hashCode() method itself.
return hashCode();
}
else if (method.getDeclaringClass() == DecoratingProxy.class) {
// There is only getDecoratedClass() declared -> dispatch to proxy config.
return AopProxyUtils.ultimateTargetClass(this.advised);
}
else if (!this.advised.opaque && method.getDeclaringClass().isInterface() &&
method.getDeclaringClass().isAssignableFrom(Advised.class)) {
// Service invocations on ProxyConfig with the proxy config...
return AopUtils.invokeJoinpointUsingReflection(this.advised, method, args);
}
Object retVal;
//目标对象内部的自我调节无法实现切换的增强则需要通过此属性暴露代理
if (this.advised.exposeProxy) {
// Make invocation available if necessary.
oldProxy = AopContext.setCurrentProxy(proxy);
setProxyContext = true;
}
// May be null. Get as late as possible to minimize the time we "own" the target,
// in case it comes from a pool.
target = targetSource.getTarget();
if (target != null) {
targetClass = target.getClass();
}
// 获取当前方法的拦截链
List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
// Check whether we have any advice. If we don't, we can fallback on direct
// reflective invocation of the target, and avoid creating a MethodInvocation.
if (chain.isEmpty()) {
// 如果没有发现任何拦截器就直接调用切点方法
Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
retVal = AopUtils.invokeJoinpointUsingReflection(target, method, argsToUse);
}
else {
// 将拦截器封装在ReflectiveMethodInvocation，以便使用其proceed方法进行链接表用链接器
invocation = new public Object proceed() throws Throwable {
// We start with an index of -1 and increment early.
if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) {
return invokeJoinpoint();
}
Object interceptorOrInterceptionAdvice =
this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex);
if (interceptorOrInterceptionAdvice instanceof InterceptorAndDynamicMethodMatcher) {
// Evaluate dynamic method matcher here: static part will already have
// been evaluated and found to match.
InterceptorAndDynamicMethodMatcher dm =
(InterceptorAndDynamicMethodMatcher) interceptorOrInterceptionAdvice;
if (dm.methodMatcher.matches(this.method, this.targetClass, this.arguments)) {
return dm.interceptor.invoke(this);
}
else {
// Dynamic matching failed.
// Skip this interceptor and invoke the next in the chain.
return proceed();
}
}
else {
// It's an interceptor, so we just invoke it: The pointcut will have
// been evaluated statically before this object was constructed.
return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
}
}(proxy, target, method, args, targetClass, chain);
// 执行链接器链
retVal = invocation.proceed();
}
// Massage return value if necessary.
Class<?> returnType = method.getReturnType();
if (retVal != null && retVal == target &&
returnType != Object.class && returnType.isInstance(proxy) &&
!RawTargetAccess.class.isAssignableFrom(method.getDeclaringClass())) {
// Special case: it returned "this" and the return type of the method
// is type-compatible. Note that we can't help if the target sets
// a reference to itself in another returned object.
retVal = proxy;
}
else if (retVal == null && returnType != Void.TYPE && returnType.isPrimitive()) {
throw new AopInvocationException(
"Null return value from advice does not match primitive return type for: " + method);
}
return retVal;
}
finally {
if (target != null && !targetSource.isStatic()) {
// Must have come from TargetSource.
targetSource.releaseTarget(target);
}
if (setProxyContext) {
// Restore old proxy.
AopContext.setCurrentProxy(oldProxy);
}
}
}
上面方法主要创建链一个拦截器链，并将拦截器封装在ReflectiveMethodInvocation，以便使用其proceed方法进行链接表用链接器
public Object proceed() throws Throwable {
// 执行完所有增强后执行切点方法
if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) {
return invokeJoinpoint();
}
//获取下一个要执行的拦截器
Object interceptorOrInterceptionAdvice =
this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex);
if (interceptorOrInterceptionAdvice instanceof InterceptorAndDynamicMethodMatcher) {
// Evaluate dynamic method matcher here: static part will already have
// 动态匹配
InterceptorAndDynamicMethodMatcher dm =
(InterceptorAndDynamicMethodMatcher) interceptorOrInterceptionAdvice;
if (dm.methodMatcher.matches(this.method, this.targetClass, this.arguments)) {
return dm.interceptor.invoke(this);
}
else {
// 不匹配则不执行拦截器
return proceed();
}
}
else {
// 普通拦截器，直接调用拦截器
// 将this作为参数传递以保证当前实例中调用链的执行
return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
}
}
ReflectiveMethodInvocation主要作用是维护链链接调用的计数器，记录当前调用链接的位置，以便链可以有序地进行下去。
2、CGLIB代理
CGLIB是一个强大、高性能的字节码生成库，它用于在运行时扩展Java类和实现接口；本质上它是通过动态的生成一个子类去覆盖所要代理的类（非final修饰的类和方法）。Enhancer是一个非常重要的类，它允许为非接口类型创建一个JAVA代理，Enhancer动态的创建给定类的子类并且拦截代理类的所有的方法，和JDK动态代理不一样的是不管是接口还是类它都能正常工作。
CGLIB被许多AOP框架使用，比如SpringAOP和dynaop，为他们提供方法的interception（拦截）。
- net.sf.cglib.proxy.Callback接口：在cglib包中是一个很关键的接口，所有被net.sf.cglib.proxy.Enhancer类调用的回调（callback）接口都要继承这个接口。
- net.sf.cglib.proxy.MethodInterceptor接口:是通用的回调（callback）类型，他经常被AOP用来实现拦截（intercept）方法的调用；
CGLIB使用示例
public class EnhancerDemo {
public static void main(String[] args) {
Enhancer enhancer = new Enhancer();
enhancer.setSuperclass(EnhancerDemo.class);
enhancer.setCallback(new MethodInterceptorImpl());
EnhancerDemo demo = (EnhancerDemo) enhancer.create();
demo.test();
System.out.println(demo);
}
public void test(){
System.out.println("EnhancerDemo test()");
}
private static class MethodInterceptorImpl implements MethodInterceptor{
@Override
public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
System.out.println("Before invoke" + method);
Object result = methodProxy.invokeSuper(o, objects);
System.out.println("Before after" + method);
return result;
}
}
}
运行结果：
Before invokepublic void EnhancerDemo.test()
EnhancerDemo test()
Before afterpublic void com.jesper.seckill.cglib.EnhancerDemo.test()
Before invokepublic java.lang.String java.lang.Object.toString()
Before invokepublic native int java.lang.Object.hashCode()
Before afterpublic native int java.lang.Object.hashCode()
Before afterpublic java.lang.String java.lang.Object.toString()
EnhancerDemo$$EnhancerByCGLIB$$c2c14280@7fac631b
完成CGLIB代理的类是委托给CglibAopProxy类去实现的，入口是getProxy()，具体如下：
public Object getProxy(ClassLoader classLoader) {
if (logger.isDebugEnabled()) {
logger.debug("Creating CGLIB proxy: target source is " + this.advised.getTargetSource());
}
try {
Class<?> rootClass = this.advised.getTargetClass();
Assert.state(rootClass != null, "Target class must be available for creating a CGLIB proxy");
Class<?> proxySuperClass = rootClass;
if (ClassUtils.isCglibProxyClass(rootClass)) {
proxySuperClass = rootClass.getSuperclass();
Class<?>[] additionalInterfaces = rootClass.getInterfaces();
for (Class<?> additionalInterface : additionalInterfaces) {
this.advised.addInterface(additionalInterface);
}
}
// 验证Class
validateClassIfNecessary(proxySuperClass, classLoader);
// 创建及配置Enhancer
Enhancer enhancer = createEnhancer();
if (classLoader != null) {
enhancer.setClassLoader(classLoader);
if (classLoader instanceof SmartClassLoader &&
((SmartClassLoader) classLoader).isClassReloadable(proxySuperClass)) {
enhancer.setUseCache(false);
}
}
enhancer.setSuperclass(proxySuperClass);
enhancer.setInterfaces(AopProxyUtils.completeProxiedInterfaces(this.advised));
enhancer.setNamingPolicy(SpringNamingPolicy.INSTANCE);
enhancer.setStrategy(new ClassLoaderAwareUndeclaredThrowableStrategy(classLoader));
//设置拦截器
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);
// 生成代理类以及创建代理
return createProxyClassAndInstance(enhancer, callbacks);
}
catch (CodeGenerationException ex) {
throw new AopConfigException("Could not generate CGLIB subclass of class [" +
this.advised.getTargetClass() + "]: " +
"Common causes of this problem include using a final class or a non-visible class",
ex);
}
catch (IllegalArgumentException ex) {
throw new AopConfigException("Could not generate CGLIB subclass of class [" +
this.advised.getTargetClass() + "]: " +
"Common causes of this problem include using a final class or a non-visible class",
ex);
}
catch (Throwable ex) {
// TargetSource.getTarget() failed
throw new AopConfigException("Unexpected AOP exception", ex);
}
}
上面是创建Spring的Enhancer的过程，主要是通过getCallbacks方法设置拦截器链
private Callback[] getCallbacks(Class<?> rootClass) throws Exception {
// Parameters used for optimization choices...
boolean exposeProxy = this.advised.isExposeProxy();
boolean isFrozen = this.advised.isFrozen();
boolean isStatic = this.advised.getTargetSource().isStatic();
// 将拦截器封装在DynamicAdvisedInterceptor中
Callback aopInterceptor = new DynamicAdvisedInterceptor(this.advised);
// Choose a "straight to target" interceptor. (used for calls that are
// unadvised but can return this). May be required to expose the proxy.
Callback targetInterceptor;
if (exposeProxy) {
targetInterceptor = isStatic ?
new StaticUnadvisedExposedInterceptor(this.advised.getTargetSource().getTarget()) :
new DynamicUnadvisedExposedInterceptor(this.advised.getTargetSource());
}
else {
targetInterceptor = isStatic ?
new StaticUnadvisedInterceptor(this.advised.getTargetSource().getTarget()) :
new DynamicUnadvisedInterceptor(this.advised.getTargetSource());
}
// Choose a "direct to target" dispatcher (used for
// unadvised calls to static targets that cannot return this).
Callback targetDispatcher = isStatic ?
new StaticDispatcher(this.advised.getTargetSource().getTarget()) : new SerializableNoOp();
Callback[] mainCallbacks = new Callback[] {
aopInterceptor, // 将拦截器链加入Callback中
targetInterceptor, // invoke target without considering advice, if optimized
new SerializableNoOp(), // no override for methods mapped to this
targetDispatcher, this.advisedDispatcher,
new EqualsInterceptor(this.advised),
new HashCodeInterceptor(this.advised)
};
Callback[] callbacks;
// If the target is a static one and the advice chain is frozen,
// then we can make some optimizations by sending the AOP calls
// direct to the target using the fixed chain for that method.
if (isStatic && isFrozen) {
Method[] methods = rootClass.getMethods();
Callback[] fixedCallbacks = new Callback[methods.length];
this.fixedInterceptorMap = new HashMap<String, Integer>(methods.length);
// TODO: small memory optimization here (can skip creation for methods with no advice)
for (int x = 0; x < methods.length; x++) {
List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(methods[x], rootClass);
fixedCallbacks[x] = new FixedChainStaticTargetInterceptor(
chain, this.advised.getTargetSource().getTarget(), this.advised.getTargetClass());
this.fixedInterceptorMap.put(methods[x].toString(), x);
}
// Now copy both the callbacks from mainCallbacks
// and fixedCallbacks into the callbacks array.
callbacks = new Callback[mainCallbacks.length + fixedCallbacks.length];
System.arraycopy(mainCallbacks, 0, callbacks, 0, mainCallbacks.length);
System.arraycopy(fixedCallbacks, 0, callbacks, mainCallbacks.length, fixedCallbacks.length);
this.fixedInterceptorOffset = mainCallbacks.length;
}
else {
callbacks = mainCallbacks;
}
return callbacks;
}
上面将advised属性封装成DynamicAdvisedInterceptor并加入callbacks，CGLIB中对于方法的拦截是通过自定义的拦截器（实现MethodInterceptor接口）加入Callback中并调用代理时直接**拦截器的intercept方法来实现的。因此，对于CGLIB方法实现的代理，其核心逻辑必然在DynamicAdvisedInterceptor中的intercept方法
public Object intercept(Object proxy, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
Object oldProxy = null;
boolean setProxyContext = false;
Class<?> targetClass = null;
Object target = null;
try {
if (this.advised.exposeProxy) {
// Make invocation available if necessary.
oldProxy = AopContext.setCurrentProxy(proxy);
setProxyContext = true;
}
// May be null. Get as late as possible to minimize the time we
// "own" the target, in case it comes from a pool...
target = getTarget();
if (target != null) {
targetClass = target.getClass();
}
//获取拦截器链
List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
Object retVal;
// Check whether we only have one InvokerInterceptor: that is,
// no real advice, but just reflective invocation of the target.
if (chain.isEmpty() && Modifier.isPublic(method.getModifiers())) {
// 如果拦截器链为空则直接**原方法
Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
retVal = methodProxy.invoke(target, argsToUse);
}
else {
//进入链
retVal = new CglibMethodInvocation(proxy, target, method, args, targetClass, chain, methodProxy).proceed();
}
retVal = processReturnType(proxy, target, method, retVal);
return retVal;
}
finally {
if (target != null) {
releaseTarget(target);
}
if (setProxyContext) {
// Restore old proxy.
AopContext.setCurrentProxy(oldProxy);
}
}
}
上面的实现与JDK方法实现的invoke方法差不多，都是首先构造链，然后封装此链进行串联调用。
总结
- 创建代理之前需要获取增强方法或增强器，获取过程需要对标记为AspectJ注解的类进行增强器的提取，根据不同的注解类型封装不同的增强器
- 创建代理实现分为JDK动态代理和CGLIB代理，如果目标对象实现了接口，默认情况会使用JDK动态代理，否则是采用CGLIB代理，CGLIB代理是通过动态的生成一个子类去覆盖所要代理的类（非final修饰的类和方法），不管是接口还是类都可以代理，Spring会自动在JDK动态代理和CGLIB之间转换。
- JDK动态代理的invoke方法和CGLIB代理的intercept方法核心逻辑大同小异，都是首先构造拦截器链，然后封装此链进行串联调用。
参考《Spring源码深度解析》