Spring AOP底层实现分析

蔚落 2022-05-10 02:36 197阅读 0赞

## Spring AOP代理对象的生成 ##

Spring提供了两种方式来生成代理对象: JdkProxy和**[Cglib][]**，具体使用哪种方式生成由AopProxyFactory根据AdvisedSupport对象的配置来决定。默认的策略是如果目标类是接口，则使用JDK动态代理技术，否则使用Cglib来生成代理。

![Image 1][]

aop.png

具体逻辑在 `org.springframework.aop.framework.DefaultAopProxyFactory`类中，源码如下：

/**
     * Spring AOP代理工厂
     */
    public class DefaultAopProxyFactory implements AopProxyFactory, Serializable {
    
        @Override
        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.");
                }
                //如果目标类是接口, 使用JDK动态代理来生成代理类及代理类实例对象
                if (targetClass.isInterface() || Proxy.isProxyClass(targetClass)) {
                    return new JdkDynamicAopProxy(config);
                }
                //使用Cglib生成代理类及代理类实例对象
                return new ObjenesisCglibAopProxy(config);
            }
            else {
                return new JdkDynamicAopProxy(config);
            }
        }
    
        private boolean hasNoUserSuppliedProxyInterfaces(AdvisedSupport config) {
            Class<?>[] ifcs = config.getProxiedInterfaces();
            return (ifcs.length == 0 || (ifcs.length == 1 && SpringProxy.class.isAssignableFrom(ifcs[0])));
        }
    
    }

### JDK动态代理技术生成代理类及实例对象 ###

下面我们来研究一下Spring如何使用JDK来生成代理对象，具体的生成代码放在`org.springframework.aop.framework.JdkDynamicAopProxy` 这个类中，直接上相关代码：

/**
     * JDK动态代理实现类
     */
    final class JdkDynamicAopProxy implements AopProxy, InvocationHandler, Serializable {
    
        /** use serialVersionUID from Spring 1.2 for interoperability */
        private static final long serialVersionUID = 5531744639992436476L;
    
        /** We use a static Log to avoid serialization issues */
        private static final Log logger = LogFactory.getLog(JdkDynamicAopProxy.class);
    
        /** Config used to configure this proxy */
        private final AdvisedSupport advised;
    
        /**
         * Is the {@link #equals} method defined on the proxied interfaces?
         */
        private boolean equalsDefined;
    
        /**
         * Is the {@link #hashCode} method defined on the proxied interfaces?
         */
        private boolean hashCodeDefined;
    
    
        /**
         * Construct a new JdkDynamicAopProxy for the given AOP configuration.
         * @param config the AOP configuration as AdvisedSupport object
         * @throws AopConfigException if the config is invalid. We try to throw an informative
         * exception in this case, rather than let a mysterious failure happen later.
         */
        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;
        }
    
        /**
         * 使用JDK动态代理生成代理类
         */
        @Override
        public Object getProxy() {
            return getProxy(ClassUtils.getDefaultClassLoader());
        }
    
        @Override
        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);
            return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
        }
    
        /**
         * Finds any {@link #equals} or {@link #hashCode} method that may be defined
         * on the supplied set of interfaces.
         * @param proxiedInterfaces the interfaces to introspect
         */
        private void findDefinedEqualsAndHashCodeMethods(Class<?>[] proxiedInterfaces) {
            for (Class<?> proxiedInterface : proxiedInterfaces) {
                Method[] methods = proxiedInterface.getDeclaredMethods();
                for (Method method : methods) {
                    if (AopUtils.isEqualsMethod(method)) {
                        this.equalsDefined = true;
                    }
                    if (AopUtils.isHashCodeMethod(method)) {
                        this.hashCodeDefined = true;
                    }
                    if (this.equalsDefined && this.hashCodeDefined) {
                        return;
                    }
                }
            }
        }
    }

JdkDynamicAopProxy 同时实现了AopProxy和InvocationHandler接口，InvocationHandler是JDK动态代理的核心，生成的代理对象的方法调用都会委托到InvocationHandler.invoke()方法。下面我们就通过分析这个类中实现的invoke()方法来具体看下Spring AOP是如何织入切面的。

@Override
        public Object invoke(Object proxy, Method method, Object[] args) 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)) {   //目标类没有实现eqauls()方法
                    // The target does not implement the equals(Object) method itself.
                    return equals(args[0]);
                }
                else if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)) {  //目标类没有实现hashCode()方法
                    // 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;
    
                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();
                }
    
                // Get the interception chain for this method.
                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()) {
                    // We can skip creating a MethodInvocation: just invoke the target directly
                    // Note that the final invoker must be an InvokerInterceptor so we know it does
                    // nothing but a reflective operation on the target, and no hot swapping or fancy proxying.
                    Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
                    retVal = AopUtils.invokeJoinpointUsingReflection(target, method, argsToUse);
                }
                else {
                    // We need to create a method invocation...
                    invocation = new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
                    // Proceed to the joinpoint through the interceptor chain.
                    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);
                }
            }
        }

主流程可以简述为：获取可以应用到此方法上的通知链（Interceptor Chain），如果有，则应用通知，并执行joinpoint；如果通知链为空，则直接反射执行joinpoint。

而这里的关键是通知链是如何获取的以及它又是如何执行的，下面逐一分析下。

首先，从上面的代码可以看到，通知链是通过AdvisedSupport.getInterceptorsAndDynamicInterceptionAdvice()这个方法来获取的,我们来看下这个方法的实现:

public List<Object> getInterceptorsAndDynamicInterceptionAdvice(Method method, Class<?> targetClass) {
            MethodCacheKey cacheKey = new MethodCacheKey(method);
            List<Object> cached = this.methodCache.get(cacheKey);
            if (cached == null) {
                cached = this.advisorChainFactory.getInterceptorsAndDynamicInterceptionAdvice(
                        this, method, targetClass);
                this.methodCache.put(cacheKey, cached);
            }
            return cached;
        }

可以看到实际的获取工作其实是由`org.springframework.aop.framework.AdvisorChainFactory`的 getInterceptorsAndDynamicInterceptionAdvice()这个方法来完成的，获取到的结果会被缓存。  
AdvisorChainFactory接口只有一个默认实现类 ：`DefaultAdvisorChainFactory`，下面来分析下这个类的实现：

package org.springframework.aop.framework;
    
    @SuppressWarnings("serial")
    public class DefaultAdvisorChainFactory implements AdvisorChainFactory, Serializable {
    
        @Override
        public List<Object> getInterceptorsAndDynamicInterceptionAdvice(
                Advised config, Method method, Class<?> targetClass) {
    
            // This is somewhat tricky... We have to process introductions first,
            // but we need to preserve order in the ultimate list.
            List<Object> interceptorList = new ArrayList<Object>(config.getAdvisors().length);
            Class<?> actualClass = (targetClass != null ? targetClass : method.getDeclaringClass());
            //查看是否包含IntroductionAdvisor  
            boolean hasIntroductions = hasMatchingIntroductions(config, actualClass);
            
            //用于将Advisor转化成MethodInterceptor
            AdvisorAdapterRegistry registry = GlobalAdvisorAdapterRegistry.getInstance();
    
            for (Advisor advisor : config.getAdvisors()) {
                if (advisor instanceof PointcutAdvisor) {
                    // Add it conditionally.
                    PointcutAdvisor pointcutAdvisor = (PointcutAdvisor) advisor;
                    if (config.isPreFiltered() || pointcutAdvisor.getPointcut().getClassFilter().matches(actualClass)) {
                        //将Advisor转化成Interceptor  
                        MethodInterceptor[] interceptors = registry.getInterceptors(advisor);
                        
                        //检查当前advisor的pointcut是否可以匹配当前方法  
                        MethodMatcher mm = pointcutAdvisor.getPointcut().getMethodMatcher();
                        if (MethodMatchers.matches(mm, method, actualClass, hasIntroductions)) {
                            if (mm.isRuntime()) {
                                // Creating a new object instance in the getInterceptors() method
                                // isn't a problem as we normally cache created chains.
                                for (MethodInterceptor interceptor : interceptors) {
                                    interceptorList.add(new InterceptorAndDynamicMethodMatcher(interceptor, mm));
                                }
                            }
                            else {
                                interceptorList.addAll(Arrays.asList(interceptors));
                            }
                        }
                    }
                }
                else if (advisor instanceof IntroductionAdvisor) {
                    IntroductionAdvisor ia = (IntroductionAdvisor) advisor;
                    if (config.isPreFiltered() || ia.getClassFilter().matches(actualClass)) {
                        Interceptor[] interceptors = registry.getInterceptors(advisor);
                        interceptorList.addAll(Arrays.asList(interceptors));
                    }
                }
                else {
                    Interceptor[] interceptors = registry.getInterceptors(advisor);
                    interceptorList.addAll(Arrays.asList(interceptors));
                }
            }
    
            return interceptorList;
        }
    
        /**
         * Determine whether the Advisors contain matching introductions.
         */
        private static boolean hasMatchingIntroductions(Advised config, Class<?> actualClass) {
            for (int i = 0; i < config.getAdvisors().length; i++) {
                Advisor advisor = config.getAdvisors()[i];
                if (advisor instanceof IntroductionAdvisor) {
                    IntroductionAdvisor ia = (IntroductionAdvisor) advisor;
                    if (ia.getClassFilter().matches(actualClass)) {
                        return true;
                    }
                }
            }
            return false;
        }
    
    }

这个方法执行完成后，Advised中配置能够应用到连接点或者目标类的Advisor全部被转化成了MethodInterceptor.

接下来，回到 `JdkDynamicAopProxy`的 invoke方法中，如下：

// 获取这个方法上的拦截器链
        List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
    
        if (chain.isEmpty()) {
            //直接调用
            Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
            retVal = AopUtils.invokeJoinpointUsingReflection(target, method, argsToUse);
        }
        else {
            // 创建MethodInvocation
            invocation = new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
            // Proceed to the joinpoint through the interceptor chain.
            retVal = invocation.proceed();
        }

从这段代码可以看出，如果得到的拦截器链为空，则直接反射调用目标方法，否则创建ReflectiveMethodInvocation，调用其proceed方法，触发拦截器链的执行，来看下 `ReflectiveMethodInvocation` 的proceed() 方法源码：

@Override
        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);
            }
        }
    
        /**
         * Invoke the joinpoint using reflection.
         * Subclasses can override this to use custom invocation.
         * @return the return value of the joinpoint
         * @throws Throwable if invoking the joinpoint resulted in an exception
         */
        protected Object invokeJoinpoint() throws Throwable {
            return AopUtils.invokeJoinpointUsingReflection(this.target, this.method, this.arguments);
        }

### Cglib生成代理类及实例对象 ###

接下来的分析会涉及到Cglib 使用，对Cglib不熟悉的同学，先看看 \[Cglib Tutorial\] ([https://github.com/cglib/cglib/wiki/Tutorial][https_github.com_cglib_cglib_wiki_Tutorial])。

Spring AOP中使用Cglib生成动态代理的类是  
`org.springframework.aop.framework.ObjenesisCglibAopProxy` ，它继承自 `org.springframework.aop.framework.CglibAopProxy`，我们首先来看看CglibAopProxy 的源码：

/**
     * Cglib动态代理实现类
     */
    class CglibAopProxy implements AopProxy, Serializable {
    
        // Constants for CGLIB callback array indices
        private static final int AOP_PROXY = 0;
        private static final int INVOKE_TARGET = 1;
        private static final int NO_OVERRIDE = 2;
        private static final int DISPATCH_TARGET = 3;
        private static final int DISPATCH_ADVISED = 4;
        private static final int INVOKE_EQUALS = 5;
        private static final int INVOKE_HASHCODE = 6;
    
    
        /** Logger available to subclasses; static to optimize serialization */
        protected static final Log logger = LogFactory.getLog(CglibAopProxy.class);
    
        /** Keeps track of the Classes that we have validated for final methods */
        private static final Map<Class<?>, Boolean> validatedClasses = new WeakHashMap<Class<?>, Boolean>();
    
    
        /** The configuration used to configure this proxy */
        protected final AdvisedSupport advised;
    
        protected Object[] constructorArgs;
    
        protected Class<?>[] constructorArgTypes;
    
        /** Dispatcher used for methods on Advised */
        private final transient AdvisedDispatcher advisedDispatcher;
    
        private transient Map<String, Integer> fixedInterceptorMap;
    
        private transient int fixedInterceptorOffset;
    
        public CglibAopProxy(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;
            this.advisedDispatcher = new AdvisedDispatcher(this.advised);
        }
        
            @Override
        public Object getProxy() {
            return getProxy(null);
        }
    
        @Override
        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);
                    }
                }
    
                // Validate the class, writing log messages as necessary.
                validateClassIfNecessary(proxySuperClass, classLoader);
    
                // Cglib Enhancer配置
                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));
    
                // Cglib 动态代理核心
                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);
    
                // 生成动态代理类和代理类实例
                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 (Exception ex) {
                // TargetSource.getTarget() failed
                throw new AopConfigException("Unexpected AOP exception", ex);
            }
        }
    
        protected Object createProxyClassAndInstance(Enhancer enhancer, Callback[] callbacks) {
            enhancer.setInterceptDuringConstruction(false);
            //设置方法回调
            enhancer.setCallbacks(callbacks);
            return (this.constructorArgs != null ?
                    enhancer.create(this.constructorArgTypes, this.constructorArgs) :
                    enhancer.create());
        }
    }

CglibAopProxy 和 JdkDynamicAopProxy类一样 实现了 `org.springframework.aop.framework.AopProxy`接口。

既然使用Cglib来生成代理类，那么其生成的代理对象的方法调用都会委托到Callback，我们来看一下 getCallbacks() 方法，源码如下：

private Callback[] getCallbacks(Class<?> rootClass) throws Exception {
            // Parameters used for optimisation choices...
            boolean exposeProxy = this.advised.isExposeProxy();
            boolean isFrozen = this.advised.isFrozen();
            boolean isStatic = this.advised.getTargetSource().isStatic();
    
            // Choose an "aop" interceptor (used for AOP calls).
            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,  // for normal advice
                    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 optimisations 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 optimisation 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;
        }

ObjenesisCglibAopProxy 类源码如下：

class ObjenesisCglibAopProxy extends CglibAopProxy {
    
        private static final Log logger = LogFactory.getLog(ObjenesisCglibAopProxy.class);
    
        private static final SpringObjenesis objenesis = new SpringObjenesis();
    
    
        /**
         * Create a new ObjenesisCglibAopProxy for the given AOP configuration.
         * @param config the AOP configuration as AdvisedSupport object
         */
        public ObjenesisCglibAopProxy(AdvisedSupport config) {
            super(config);
        }
    
    
        @Override
        @SuppressWarnings("unchecked")
        protected Object createProxyClassAndInstance(Enhancer enhancer, Callback[] callbacks) {
            Class<?> proxyClass = enhancer.createClass();
            Object proxyInstance = null;
    
            if (objenesis.isWorthTrying()) {
                try {
                    proxyInstance = objenesis.newInstance(proxyClass, enhancer.getUseCache());
                }
                catch (Throwable ex) {
                    logger.debug("Unable to instantiate proxy using Objenesis, " +
                            "falling back to regular proxy construction", ex);
                }
            }
    
            if (proxyInstance == null) {
                // Regular instantiation via default constructor...
                try {
                    proxyInstance = (this.constructorArgs != null ?
                            proxyClass.getConstructor(this.constructorArgTypes).newInstance(this.constructorArgs) :
                            proxyClass.newInstance());
                }
                catch (Throwable ex) {
                    throw new AopConfigException("Unable to instantiate proxy using Objenesis, " +
                            "and regular proxy instantiation via default constructor fails as well", ex);
                }
            }
    
            ((Factory) proxyInstance).setCallbacks(callbacks);
            return proxyInstance;
        }
    
    }

ObjenesisCglibAopProxy 重写了父类 `CglibAopProxy` 中的createProxyClassAndInstance方法，使用 [Objenesis][]来生成代理类实例对象。

SpringObjenesis 源码如下：

package org.springframework.objenesis;
    
    import org.springframework.core.SpringProperties;
    import org.springframework.objenesis.Objenesis;
    import org.springframework.objenesis.ObjenesisException;
    import org.springframework.objenesis.instantiator.ObjectInstantiator;
    import org.springframework.objenesis.strategy.InstantiatorStrategy;
    import org.springframework.objenesis.strategy.StdInstantiatorStrategy;
    import org.springframework.util.ConcurrentReferenceHashMap;
    
    public class SpringObjenesis implements Objenesis {
        public static final String IGNORE_OBJENESIS_PROPERTY_NAME = "spring.objenesis.ignore";
        private final InstantiatorStrategy strategy;
        private final ConcurrentReferenceHashMap<Class<?>, ObjectInstantiator<?>> cache;
        private volatile Boolean worthTrying;
    
        public SpringObjenesis() {
            this((InstantiatorStrategy)null);
        }
    
        public SpringObjenesis(InstantiatorStrategy strategy) {
            this.cache = new ConcurrentReferenceHashMap();
            this.strategy = (InstantiatorStrategy)(strategy != null?strategy:new StdInstantiatorStrategy());
            if(SpringProperties.getFlag("spring.objenesis.ignore")) {
                this.worthTrying = Boolean.FALSE;
            }
    
        }
    
        public boolean isWorthTrying() {
            return this.worthTrying != Boolean.FALSE;
        }
    
        public <T> T newInstance(Class<T> clazz, boolean useCache) {
            return !useCache?this.newInstantiatorOf(clazz).newInstance():this.getInstantiatorOf(clazz).newInstance();
        }
    
        public <T> T newInstance(Class<T> clazz) {
            return this.getInstantiatorOf(clazz).newInstance();
        }
    
        public <T> ObjectInstantiator<T> getInstantiatorOf(Class<T> clazz) {
            ObjectInstantiator instantiator = (ObjectInstantiator)this.cache.get(clazz);
            if(instantiator == null) {
                ObjectInstantiator newInstantiator = this.newInstantiatorOf(clazz);
                instantiator = (ObjectInstantiator)this.cache.putIfAbsent(clazz, newInstantiator);
                if(instantiator == null) {
                    instantiator = newInstantiator;
                }
            }
    
            return instantiator;
        }
    
        protected <T> ObjectInstantiator<T> newInstantiatorOf(Class<T> clazz) {
            Boolean currentWorthTrying = this.worthTrying;
    
            try {
                ObjectInstantiator err = this.strategy.newInstantiatorOf(clazz);
                if(currentWorthTrying == null) {
                    this.worthTrying = Boolean.TRUE;
                }
    
                return err;
            } catch (ObjenesisException var5) {
                if(currentWorthTrying == null) {
                    Throwable cause = var5.getCause();
                    if(cause instanceof ClassNotFoundException || cause instanceof IllegalAccessException) {
                        this.worthTrying = Boolean.FALSE;
                    }
                }
    
                throw var5;
            } catch (NoClassDefFoundError var6) {
                if(currentWorthTrying == null) {
                    this.worthTrying = Boolean.FALSE;
                }
    
                throw new ObjenesisException(var6);
            }
        }
    }

到此，关于Spring AOP内部实现原理分析就结束了。

作者：FX\_SKY  
链接：https://www.jianshu.com/p/16a2ad9f4fbc  
來源：简书  
简书著作权归作者所有，任何形式的转载都请联系作者获得授权并注明出处。

[Cglib]: https://link.jianshu.com?t=https://github.com/cglib/cglib
[Image 1]: 
[https_github.com_cglib_cglib_wiki_Tutorial]: https://link.jianshu.com?t=https://github.com/cglib/cglib/wiki/Tutorial
[Objenesis]: https://link.jianshu.com?t=http://objenesis.org/