《Spring设计思想》AOP实现原理（基于JDK和基于CGLIB）

0、前言

     在上篇文章 《Spring设计思想》AOP设计基本原理 中阐述了Spring AOP 的基本原理以及基本机制，本文将深入源码，详细阐述整个Spring AOP实现的整个过程。

    

读完本文，你将了解到：

1、Spring内部创建代理对象的过程
2、Spring AOP的核心---ProxyFactoryBean
3、基于JDK面向接口的动态代理JdkDynamicAopProxy生成代理对象
4、基于Cglib子类继承方式的动态代理CglibAopProxy生成代理对象
5、各种Advice是的执行顺序是如何和方法调用进行结合的？
6、PointCut与Advice的结合------Adivce的条件执行
7、总结

1、Spring内部创建代理对象的过程

            在Spring的底层，如果我们配置了代理模式，Spring会为每一个Bean创建一个对应的ProxyFactoryBean的FactoryBean来创建某个对象的代理对象。

            假定我们现在有一个接口TicketService及其实现类RailwayStation，我们打算创建一个代理类，在执行TicketService的方法时的各个阶段，插入对应的业务代码。

package org.luanlouis.meditations.thinkinginspring.aop;

/**
 * 售票服务
 * Created by louis on 2016/4/14.
 */
public interface TicketService {

    //售票
    public void sellTicket();

    //问询
    public void inquire();

    //退票
    public void withdraw();
}

package org.luanlouis.meditations.thinkinginspring.aop;

/**
 * RailwayStation 实现 TicketService
 * Created by louis on 2016/4/14.
 */
public class RailwayStation implements TicketService {

    public void sellTicket(){
        System.out.println("售票............");
    }

    public void inquire() {
        System.out.println("问询.............");
    }

    public void withdraw() {
        System.out.println("退票.............");
    }
}

package org.luanlouis.meditations.thinkinginspring.aop;

import org.springframework.aop.MethodBeforeAdvice;

import java.lang.reflect.Method;

/**
 * 执行RealSubject对象的方法之前的处理意见
 * Created by louis on 2016/4/14.
 */
public class TicketServiceBeforeAdvice implements MethodBeforeAdvice {

    public void before(Method method, Object[] args, Object target) throws Throwable {
        System.out.println("BEFORE_ADVICE: 欢迎光临代售点....");
    }
}

package org.luanlouis.meditations.thinkinginspring.aop;

import org.springframework.aop.AfterReturningAdvice;

import java.lang.reflect.Method;

/**
 * 返回结果时后的处理意见
 * Created by louis on 2016/4/14.
 */
public class TicketServiceAfterReturningAdvice implements AfterReturningAdvice {
    @Override
    public void afterReturning(Object returnValue, Method method, Object[] args, Object target) throws Throwable {
        System.out.println("AFTER_RETURNING：本次服务已结束....");
    }
}

package org.luanlouis.meditations.thinkinginspring.aop;

import org.springframework.aop.ThrowsAdvice;

import java.lang.reflect.Method;

/**
 * 抛出异常时的处理意见
 * Created by louis on 2016/4/14.
 */
public class TicketServiceThrowsAdvice implements ThrowsAdvice {

    public void afterThrowing(Exception ex){
        System.out.println("AFTER_THROWING....");
    }
    public void afterThrowing(Method method, Object[] args, Object target, Exception ex){
        System.out.println("调用过程出错啦！！！！！");
    }

} 

package org.luanlouis.meditations.thinkinginspring.aop;

import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;
import org.springframework.aop.aspectj.AspectJAroundAdvice;

/**
 *
 * AroundAdvice
 * Created by louis on 2016/4/15.
 */
public class TicketServiceAroundAdvice implements MethodInterceptor {
    @Override
    public Object invoke(MethodInvocation invocation) throws Throwable {
        System.out.println("AROUND_ADVICE:BEGIN....");
        Object returnValue = invocation.proceed();
        System.out.println("AROUND_ADVICE:END.....");
        return returnValue;
    }
}

               现在，我们来手动使用ProxyFactoryBean来创建Proxy对象，并将相应的几种不同的Advice加入这个proxy对应的各个执行阶段中：

package org.luanlouis.meditations.thinkinginspring.aop;

import org.aopalliance.aop.Advice;
import org.springframework.aop.framework.ProxyFactoryBean;

/**
 * 通过ProxyFactoryBean 手动创建 代理对象
 * Created by louis on 2016/4/14.
 */
public class App {

    public static void main(String[] args) throws Exception {

        //1.针对不同的时期类型，提供不同的Advice
        Advice beforeAdvice = new TicketServiceBeforeAdvice();
        Advice afterReturningAdvice = new TicketServiceAfterReturningAdvice();
        Advice aroundAdvice = new TicketServiceAroundAdvice();
        Advice throwsAdvice = new TicketServiceThrowsAdvice();

        RailwayStation railwayStation = new RailwayStation();

        //2.创建ProxyFactoryBean,用以创建指定对象的Proxy对象
        ProxyFactoryBean proxyFactoryBean = new ProxyFactoryBean();
       //3.设置Proxy的接口
        proxyFactoryBean.setInterfaces(TicketService.class);
        //4. 设置RealSubject
        proxyFactoryBean.setTarget(railwayStation);
        //5.使用JDK基于接口实现机制的动态代理生成Proxy代理对象，如果想使用CGLIB，需要将这个flag设置成true
        proxyFactoryBean.setProxyTargetClass(true);

        //6. 添加不同的Advice

        proxyFactoryBean.addAdvice(afterReturningAdvice);
        proxyFactoryBean.addAdvice(aroundAdvice);
        proxyFactoryBean.addAdvice(throwsAdvice);
        proxyFactoryBean.addAdvice(beforeAdvice);
        proxyFactoryBean.setProxyTargetClass(false);
        //7通过ProxyFactoryBean生成Proxy对象
        TicketService ticketService = (TicketService) proxyFactoryBean.getObject();
        ticketService.sellTicket();

    }


}

不出意外的话，你会得到如下的输出结果：

你会看到，我们成功地创建了一个通过一个ProxyFactoryBean和 真实的实例对象创建出了对应的代理对象，并将各个Advice加入到proxy代理对象中。

你会发现，在调用RailwayStation的sellticket()之前，成功插入了BeforeAdivce逻辑，而调用RailwayStation的sellticket()之后，AfterReturning逻辑也成功插入了。

AroundAdvice也成功包裹了sellTicket()方法，只不过这个AroundAdvice发生的时机有点让人感到迷惑。实际上，这个背后的执行逻辑隐藏了Spring AOP关于AOP的关于Advice调度最为核心的算法机制，这个将在本文后面详细阐述。

另外，本例中ProxyFactoryBean是通过JDK的针对接口的动态代理模式生成代理对象的，具体机制，请看下面关于ProxyFactoryBean的介绍。

2、Spring AOP的核心---ProxyFactoryBean

          上面我们通过了纯手动使用ProxyFactoryBean实现了AOP的功能。现在来分析一下上面的代码：我们为ProxyFactoryBean提供了如下信息：

1). Proxy应该感兴趣的Adivce列表；

2). 真正的实例对象引用ticketService;

3).告诉ProxyFactoryBean使用基于接口实现的JDK动态代理机制实现proxy: 

4). Proxy应该具备的Interface接口：TicketService;

根据这些信息，ProxyFactoryBean就能给我们提供我们想要的Proxy对象了！那么，ProxyFactoryBean帮我们做了什么？

              Spring 使用工厂Bean模式创建每一个Proxy，对应每一个不同的Class类型，在Spring中都会有一个相对应的ProxyFactoryBean. 以下是ProxyFactoryBean的类图。

如上所示，对于生成Proxy的工厂Bean而言，它要知道对其感兴趣的Advice信息，而这类的信息，被维护到Advised中。Advised可以根据特定的类名和方法名返回对应的AdviceChain，用以表示需要执行的Advice串。

3、基于JDK面向接口的动态代理JdkDynamicAopProxy生成代理对象

JdkDynamicAopProxy类实现了AopProxy，能够返回Proxy，并且，其自身也实现了InvocationHandler角色。也就是说，当我们使用proxy时，我们对proxy对象调用的方法，都最终被转到这个类的invoke()方法中。

final class JdkDynamicAopProxy implements AopProxy, InvocationHandler, Serializable {
        //省略若干...
	/** Proxy的配置信息，这里主要提供Advisor列表，并用于返回AdviceChain */
	private final AdvisedSupport advised;

	/**
	 * 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;
	}


	@Override
	public Object getProxy() {
		return getProxy(ClassUtils.getDefaultClassLoader());
	}
        //返回代理实例对象
	@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);
		findDefinedEqualsAndHashCodeMethods(proxiedInterfaces);
                //这里的InvocationHandler设置成了当前实例对象，即对这个proxy调用的任何方法，都会调用这个类的invoke()方法
                //这里的invoke方法被调用，动态查找Advice列表，组成ReflectMethodInvocation
		return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
	}
	/**
	 * 对当前proxy调用其上的任何方法，都将转到这个方法上
         * Implementation of {@code InvocationHandler.invoke}.
	 * <p>Callers will see exactly the exception thrown by the target,
	 * unless a hook method throws an exception.
	 */
	@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)) {
				// The target does not implement the equals(Object) method itself.
				return equals(args[0]);
			}
			if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)) {
				// The target does not implement the hashCode() method itself.
				return hashCode();
			}
			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.获取当前调用方法的拦截链
			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.
                        //如果没有拦截链，则直接调用Joinpoint连接点的方法。
			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...
                                //根据给定的拦截链和方法调用信息，创建新的MethodInvocation对象，整个拦截链的工作逻辑都在这个ReflectiveMethodInvocation里 
				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.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);
			}
		}
	}
}

4、基于Cglib子类继承方式的动态代理CglibAopProxy生成代理对象

基于Cglib子类继承方式的动态代理CglibAopProxy生成代理对象：

package org.springframework.aop.framework;
/**
 * CGLIB-based {@link AopProxy} implementation for the Spring AOP framework.
 *
 * <p>Formerly named {@code Cglib2AopProxy}, as of Spring 3.2, this class depends on
 * Spring's own internally repackaged version of CGLIB 3.</i>.
 */
@SuppressWarnings("serial")
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;


	/**
	 * Create a new CglibAopProxy 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 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);
	}

	/**
	 * Set constructor arguments to use for creating the proxy.
	 * @param constructorArgs the constructor argument values
	 * @param constructorArgTypes the constructor argument types
	 */
	public void setConstructorArguments(Object[] constructorArgs, Class<?>[] constructorArgTypes) {
		if (constructorArgs == null || constructorArgTypes == null) {
			throw new IllegalArgumentException("Both 'constructorArgs' and 'constructorArgTypes' need to be specified");
		}
		if (constructorArgs.length != constructorArgTypes.length) {
			throw new IllegalArgumentException("Number of 'constructorArgs' (" + constructorArgs.length +
					") must match number of 'constructorArgTypes' (" + constructorArgTypes.length + ")");
		}
		this.constructorArgs = constructorArgs;
		this.constructorArgTypes = constructorArgTypes;
	}


	@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);

			// Configure CGLIB 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));

			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);
		}
		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);
		enhancer.setCallbacks(callbacks);
		return (this.constructorArgs != null ?
				enhancer.create(this.constructorArgTypes, this.constructorArgs) :
				enhancer.create());
	}

	/**
	 * Creates the CGLIB {@link Enhancer}. Subclasses may wish to override this to return a custom
	 * {@link Enhancer} implementation.
	 */
	protected Enhancer createEnhancer() {
		return new Enhancer();
	}



	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;
	}


	/**
	 * General purpose AOP callback. Used when the target is dynamic or when the
	 * proxy is not frozen.
	 */
	private static class DynamicAdvisedInterceptor implements MethodInterceptor, Serializable {

		private final AdvisedSupport advised;

		public DynamicAdvisedInterceptor(AdvisedSupport advised) {
			this.advised = advised;
		}

		@Override
		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();
				}
				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())) {
					// 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 = methodProxy.invoke(target, argsToUse);
				}
				else {
					// We need to create a method invocation...
					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);
				}
			}
		}
		//省略...
	}


	/**
	 * Implementation of AOP Alliance MethodInvocation used by this AOP proxy.
	 */
	private static class CglibMethodInvocation extends ReflectiveMethodInvocation {

		private final MethodProxy methodProxy;

		private final boolean publicMethod;

		public CglibMethodInvocation(Object proxy, Object target, Method method, Object[] arguments,
				Class<?> targetClass, List<Object> interceptorsAndDynamicMethodMatchers, MethodProxy methodProxy) {

			super(proxy, target, method, arguments, targetClass, interceptorsAndDynamicMethodMatchers);
			this.methodProxy = methodProxy;
			this.publicMethod = Modifier.isPublic(method.getModifiers());
		}

		/**
		 * Gives a marginal performance improvement versus using reflection to
		 * invoke the target when invoking public methods.
		 */
		@Override
		protected Object invokeJoinpoint() throws Throwable {
			if (this.publicMethod) {
				return this.methodProxy.invoke(this.target, this.arguments);
			}
			else {
				return super.invokeJoinpoint();
			}
		}
	}

}

5、各种Advice是的执行顺序是如何和方法调用进行结合的？

JdkDynamicAopProxy 和CglibAopProxy只是创建代理方式的两种方式而已，实际上我们为方法调用添加的各种Advice的执行逻辑都是统一的。在Spring的底层，会把我们定义的各个Adivce分别 包裹成一个 MethodInterceptor,这些Advice按照加入Advised顺序，构成一个AdivseChain.

比如我们上述的代码：

        //5. 添加不同的Advice

        proxyFactoryBean.addAdvice(afterReturningAdvice);
        proxyFactoryBean.addAdvice(aroundAdvice);
        proxyFactoryBean.addAdvice(throwsAdvice);
        proxyFactoryBean.addAdvice(beforeAdvice);
        proxyFactoryBean.setProxyTargetClass(false);
        //通过ProxyFactoryBean生成
        TicketService ticketService = (TicketService) proxyFactoryBean.getObject();
        ticketService.sellTicket();

当我们调用 ticketService.sellTicket()时，Spring会把这个方法调用转换成一个MethodInvocation对象，然后结合上述的我们添加的各种Advice,组成一个ReflectiveMethodInvocation:

 各种Advice本质而言是一个方法调用拦截器，现在让我们看看各个Advice拦截器都干了什么？

/**
 * 包裹MethodBeforeAdvice的方法拦截器
 * Interceptor to wrap am {@link org.springframework.aop.MethodBeforeAdvice}.
 * Used internally by the AOP framework; application developers should not need
 * to use this class directly.
 *
 * @author Rod Johnson
 */
@SuppressWarnings("serial")
public class MethodBeforeAdviceInterceptor implements MethodInterceptor, Serializable {

	private MethodBeforeAdvice advice;


	/**
	 * Create a new MethodBeforeAdviceInterceptor for the given advice.
	 * @param advice the MethodBeforeAdvice to wrap
	 */
	public MethodBeforeAdviceInterceptor(MethodBeforeAdvice advice) {
		Assert.notNull(advice, "Advice must not be null");
		this.advice = advice;
	}

	@Override
	public Object invoke(MethodInvocation mi) throws Throwable {
		//在调用方法之前，先执行BeforeAdvice
		this.advice.before(mi.getMethod(), mi.getArguments(), mi.getThis() );
		return mi.proceed();
	}

}

/**
 * 包裹AfterReturningAdvice的方法拦截器
 * Interceptor to wrap am {@link org.springframework.aop.AfterReturningAdvice}.
 * Used internally by the AOP framework; application developers should not need
 * to use this class directly.
 *
 * @author Rod Johnson
 */
@SuppressWarnings("serial")
public class AfterReturningAdviceInterceptor implements MethodInterceptor, AfterAdvice, Serializable {

	private final AfterReturningAdvice advice;


	/**
	 * Create a new AfterReturningAdviceInterceptor for the given advice.
	 * @param advice the AfterReturningAdvice to wrap
	 */
	public AfterReturningAdviceInterceptor(AfterReturningAdvice advice) {
		Assert.notNull(advice, "Advice must not be null");
		this.advice = advice;
	}

	@Override
	public Object invoke(MethodInvocation mi) throws Throwable {
		//先调用invocation
		Object retVal = mi.proceed();
		//调用成功后，调用AfterReturningAdvice
		this.advice.afterReturning(retVal, mi.getMethod(), mi.getArguments(), mi.getThis());
		return retVal;
	}

}

/**
 * Interceptor to wrap an after-throwing advice.
 *
 * <p>The signatures on handler methods on the {@code ThrowsAdvice}
 * implementation method argument must be of the form:<br>
 *
 * {@code void afterThrowing([Method, args, target], ThrowableSubclass);}
 *
 * <p>Only the last argument is required.
 *
 * <p>Some examples of valid methods would be:
 *
 * <pre class="code">public void afterThrowing(Exception ex)</pre>
 * <pre class="code">public void afterThrowing(RemoteException)</pre>
 * <pre class="code">public void afterThrowing(Method method, Object[] args, Object target, Exception ex)</pre>
 * <pre class="code">public void afterThrowing(Method method, Object[] args, Object target, ServletException ex)</pre>
 *
 * <p>This is a framework class that need not be used directly by Spring users.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 */
public class ThrowsAdviceInterceptor implements MethodInterceptor, AfterAdvice {

	private static final String AFTER_THROWING = "afterThrowing";

	private static final Log logger = LogFactory.getLog(ThrowsAdviceInterceptor.class);


	private final Object throwsAdvice;

	/** Methods on throws advice, keyed by exception class */
	private final Map<Class<?>, Method> exceptionHandlerMap = new HashMap<Class<?>, Method>();


	/**
	 * Create a new ThrowsAdviceInterceptor for the given ThrowsAdvice.
	 * @param throwsAdvice the advice object that defines the exception
	 * handler methods (usually a {@link org.springframework.aop.ThrowsAdvice}
	 * implementation)
	 */
	public ThrowsAdviceInterceptor(Object throwsAdvice) {
		Assert.notNull(throwsAdvice, "Advice must not be null");
		this.throwsAdvice = throwsAdvice;

		Method[] methods = throwsAdvice.getClass().getMethods();
		for (Method method : methods) {
			//ThrowsAdvice定义的afterThrowing方法是Handler方法
			if (method.getName().equals(AFTER_THROWING) &&
					(method.getParameterTypes().length == 1 || method.getParameterTypes().length == 4) &&
					Throwable.class.isAssignableFrom(method.getParameterTypes()[method.getParameterTypes().length - 1])
				) {
				// Have an exception handler
				this.exceptionHandlerMap.put(method.getParameterTypes()[method.getParameterTypes().length - 1], method);
				if (logger.isDebugEnabled()) {
					logger.debug("Found exception handler method: " + method);
				}
			}
		}

		if (this.exceptionHandlerMap.isEmpty()) {
			throw new IllegalArgumentException(
					"At least one handler method must be found in class [" + throwsAdvice.getClass() + "]");
		}
	}

	public int getHandlerMethodCount() {
		return this.exceptionHandlerMap.size();
	}

	/**
	 * Determine the exception handle method. Can return null if not found.
	 * @param exception the exception thrown
	 * @return a handler for the given exception type
	 */
	private Method getExceptionHandler(Throwable exception) {
		Class<?> exceptionClass = exception.getClass();
		if (logger.isTraceEnabled()) {
			logger.trace("Trying to find handler for exception of type [" + exceptionClass.getName() + "]");
		}
		Method handler = this.exceptionHandlerMap.get(exceptionClass);
		while (handler == null && exceptionClass != Throwable.class) {
			exceptionClass = exceptionClass.getSuperclass();
			handler = this.exceptionHandlerMap.get(exceptionClass);
		}
		if (handler != null && logger.isDebugEnabled()) {
			logger.debug("Found handler for exception of type [" + exceptionClass.getName() + "]: " + handler);
		}
		return handler;
	}

	@Override
	public Object invoke(MethodInvocation mi) throws Throwable {
		//使用大的try，先执行代码，捕获异常
		try {
			return mi.proceed();
		}
		catch (Throwable ex) {
			//获取异常处理方法
			Method handlerMethod = getExceptionHandler(ex);
			//调用异常处理方法
			if (handlerMethod != null) {
				invokeHandlerMethod(mi, ex, handlerMethod);
			}
			throw ex;
		}
	}

	private void invokeHandlerMethod(MethodInvocation mi, Throwable ex, Method method) throws Throwable {
		Object[] handlerArgs;
		if (method.getParameterTypes().length == 1) {
			handlerArgs = new Object[] { ex };
		}
		else {
			handlerArgs = new Object[] {mi.getMethod(), mi.getArguments(), mi.getThis(), ex};
		}
		try {
			method.invoke(this.throwsAdvice, handlerArgs);
		}
		catch (InvocationTargetException targetEx) {
			throw targetEx.getTargetException();
		}
	}

}

关于AroundAdivce,其本身就是一个MethodInterceptor，所以不需要额外做转换了。

细心的你会发现，在拦截器串中，每个拦截器最后都会调用MethodInvocation的proceed()方法。如果按照简单的拦截器的执行串来执行的话，MethodInvocation的proceed()方法至少要执行N次(N表示拦截器Interceptor的个数)，因为每个拦截器都会调用一次proceed()方法。更直观地讲，比如我们调用了ticketService.sellTicket()方法，那么，按照这个逻辑，我们会打印出四条记录：

售票............
售票............
售票............
售票............

这样我们肯定不是我们需要的结果！！！！因为按照我们的理解，只应该有一条"售票............"才对。真实的Spring的方法调用过程能够控制这个逻辑按照我们的思路执行，Spring将这个整个方法调用过程连同若干个Advice组成的拦截器链组合成ReflectiveMethodInvocation对象，让我们来看看这一执行逻辑是怎么控制的：

public class ReflectiveMethodInvocation implements ProxyMethodInvocation, Cloneable {

	protected final Object proxy;

	protected final Object target;

	protected final Method method;

	protected Object[] arguments;

	private final Class<?> targetClass;

	/**
	 * Lazily initialized map of user-specific attributes for this invocation.
	 */
	private Map<String, Object> userAttributes;

	/**
	 * List of MethodInterceptor and InterceptorAndDynamicMethodMatcher
	 * that need dynamic checks.
	 */
	protected final List<?> interceptorsAndDynamicMethodMatchers;

	/**
	 * Index from 0 of the current interceptor we're invoking.
	 * -1 until we invoke: then the current interceptor.
	 */
	private int currentInterceptorIndex = -1;


	/**
	 * Construct a new ReflectiveMethodInvocation with the given arguments.
	 * @param proxy the proxy object that the invocation was made on
	 * @param target the target object to invoke
	 * @param method the method to invoke
	 * @param arguments the arguments to invoke the method with
	 * @param targetClass the target class, for MethodMatcher invocations
	 * @param interceptorsAndDynamicMethodMatchers interceptors that should be applied,
	 * along with any InterceptorAndDynamicMethodMatchers that need evaluation at runtime.
	 * MethodMatchers included in this struct must already have been found to have matched
	 * as far as was possibly statically. Passing an array might be about 10% faster,
	 * but would complicate the code. And it would work only for static pointcuts.
	 */
	protected ReflectiveMethodInvocation(
			Object proxy, Object target, Method method, Object[] arguments,
			Class<?> targetClass, List<Object> interceptorsAndDynamicMethodMatchers) {

		this.proxy = proxy;//proxy对象
		this.target = target;//真实的realSubject对象
		this.targetClass = targetClass;//被代理的类类型
		this.method = BridgeMethodResolver.findBridgedMethod(method);//方法引用
		this.arguments = AopProxyUtils.adaptArgumentsIfNecessary(method, arguments);//调用参数
		this.interceptorsAndDynamicMethodMatchers = interceptorsAndDynamicMethodMatchers;//Advice拦截器链
	}


	@Override
	public final Object getProxy() {
		return this.proxy;
	}

	@Override
	public final Object getThis() {
		return this.target;
	}

	@Override
	public final AccessibleObject getStaticPart() {
		return this.method;
	}

	/**
	 * Return the method invoked on the proxied interface.
	 * May or may not correspond with a method invoked on an underlying
	 * implementation of that interface.
	 */
	@Override
	public final Method getMethod() {
		return this.method;
	}

	@Override
	public final Object[] getArguments() {
		return (this.arguments != null ? this.arguments : new Object[0]);
	}

	@Override
	public void setArguments(Object... arguments) {
		this.arguments = arguments;
	}


	@Override
	public Object proceed() throws Throwable {
		//	没有拦截器，则直接调用Joinpoint上的method，即直接调用MethodInvocation We start with an index of -1 and increment early.
		if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) {
			return invokeJoinpoint();
		}
                // 取得第拦截器链上第N个拦截器 
		Object interceptorOrInterceptionAdvice =
				this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex);
		//PointcutInterceptor会走这个逻辑
                if (interceptorOrInterceptionAdvice instanceof InterceptorAndDynamicMethodMatcher) {
			// Evaluate dynamic method matcher here: static part will already have
			// been evaluated and found to match.
			InterceptorAndDynamicMethodMatcher dm =
					(InterceptorAndDynamicMethodMatcher) interceptorOrInterceptionAdvice;
			//当前拦截器是符合拦截规则，每个拦截器可以定义是否特定的类和方法名是否符合拦截规则
                        //实际上PointCut定义的方法签名最后会转换成这个MethodMatcher，并置于拦截器中
                        if (dm.methodMatcher.matches(this.method, this.targetClass, this.arguments)) {
			     //符合拦截规则，调用拦截器invoke()	
                             return dm.interceptor.invoke(this);
			}
			else {
				// Dynamic matching failed.
				// Skip this interceptor and invoke the next in the chain.
                                // 当前方法不需要拦截器操作，则直接往前推进
                                return proceed();
			}
		}
		else {
			// It's an interceptor, so we just invoke it: The pointcut will have
			// been evaluated statically before this object was constructed.
                        //直接调用拦截器，
                        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);
	}

上述的代码比较冗杂，解释起来比较繁琐，请看下面一张图，你就知道这段代码的思路了：

实例分析

根据上面的执行链上的逻辑，我们将我们上面举的例子的输出结果在整理一下：

Advice拦截器的添加顺序:

        proxyFactoryBean.addAdvice(afterReturningAdvice);
        proxyFactoryBean.addAdvice(aroundAdvice);
        proxyFactoryBean.addAdvice(throwsAdvice);
        proxyFactoryBean.addAdvice(beforeAdvice);

第一个拦截器：AfterReturningAdvice

第一个添加的是afterReturningAdivce,它所处的位置是第一个拦截器，执行的操作就是：

	@Override
	public Object invoke(MethodInvocation mi) throws Throwable {
		Object retVal = mi.proceed();
		this.advice.afterReturning(retVal, mi.getMethod(), mi.getArguments(), mi.getThis());
		return retVal;
	}

也就是说，先完成MethodInvocation的proceed()方法再执行相应的advice；而调用了mi.proceed()方法，导致了当前的调用链后移，进行和后续的操作，也就是说，AfterReturningAdvice只能等到整个拦截器链上所有执行完毕后才会生效，所以： AFTER_RETURNING:本次服务已结束.... 这句话排在了最后：

第二个拦截器：AroundAdvice

    @Override
    public Object invoke(MethodInvocation invocation) throws Throwable {
        System.out.println("AROUND_ADVICE:BEGIN....");
        Object returnValue = invocation.proceed();
        System.out.println("AROUND_ADVICE:END.....");
        return returnValue;
    }

现在执行到了第二个拦截器，首先输出了"AROUND_ADVICE:BEGIN......"，接着调用Invocation.proceed(),等到剩余的执行完后，再输出"AROUND_ADVICE:END....."：

第三个拦截器：ThrowsAdvice:

ThrowsAdvice拦截器的处理模式是：

	@Override
	public Object invoke(MethodInvocation mi) throws Throwable {
		try {
		       //先执行invocation.proceed();	
                       return mi.proceed();
		}
		catch (Throwable ex) {
                       //捕捉错误，调用afterThrowing()方法
                        Method handlerMethod = getExceptionHandler(ex);
			if (handlerMethod != null) {
				invokeHandlerMethod(mi, ex, handlerMethod);
			}
			throw ex;
		}
	}

上述的逻辑是，先执行Invocation.proceed();如果这个过程中抛出异常，则调用ThrowsAdvice。

第四个拦截器:BeforeAdvice:

这个拦截器的工作逻辑如下：

	@Override
	public Object invoke(MethodInvocation mi) throws Throwable {
		this.advice.before(mi.getMethod(), mi.getArguments(), mi.getThis() );//先执行Advice
		return mi.proceed();//后执行Invocation
	}

综上所有的拦截器过程，我们就能理解，为什么我们刚开始的输出为什么是下面这样了：

6、PointCut与Advice的结合------Adivce的条件执行

上面我们提供了几个Adivce，你会发现，这些Advice是无条件地加入了我们创建的对象中。无论调用Target的任何方法，这些Advice都会被触发到。

那么，我们可否告诉Advice，只让它对特定的方法或特定类起作用呢？ 这个实际上是要求我们添加一个过滤器，如果满足条件，则Advice生效，否则无效。Spring将这个过滤器抽象成如下的接口：

public interface MethodMatcher {

	/**
	 * 提供方法签名和所属的Class类型，判断是否支持 
         * Perform static checking whether the given method matches. If this
	 * returns {@code false} or if the {@link #isRuntime()} method
	 * returns {@code false}, no runtime check (i.e. no.
	 * {@link #matches(java.lang.reflect.Method, Class, Object[])} call) will be made.
	 * @param method the candidate method
	 * @param targetClass the target class (may be {@code null}, in which case
	 * the candidate class must be taken to be the method's declaring class)
	 * @return whether or not this method matches statically
	 */
	boolean matches(Method method, Class<?> targetClass);

	/**
	 * Is this MethodMatcher dynamic, that is, must a final call be made on the
	 * {@link #matches(java.lang.reflect.Method, Class, Object[])} method at
	 * runtime even if the 2-arg matches method returns {@code true}?
	 * <p>Can be invoked when an AOP proxy is created, and need not be invoked
	 * again before each method invocation,
	 * @return whether or not a runtime match via the 3-arg
	 * {@link #matches(java.lang.reflect.Method, Class, Object[])} method
	 * is required if static matching passed
	 */
	boolean isRuntime();

	/**
	 * Check whether there a runtime (dynamic) match for this method,
	 * which must have matched statically.
	 * <p>This method is invoked only if the 2-arg matches method returns
	 * {@code true} for the given method and target class, and if the
	 * {@link #isRuntime()} method returns {@code true}. Invoked
	 * immediately before potential running of the advice, after any
	 * advice earlier in the advice chain has run.
	 * @param method the candidate method
	 * @param targetClass the target class (may be {@code null}, in which case
	 * the candidate class must be taken to be the method's declaring class)
	 * @param args arguments to the method
	 * @return whether there's a runtime match
	 * @see MethodMatcher#matches(Method, Class)
	 */
	boolean matches(Method method, Class<?> targetClass, Object... args);


	/**
	 * Canonical instance that matches all methods.
	 */
	MethodMatcher TRUE = TrueMethodMatcher.INSTANCE;

}

将这个匹配器MethodMatcher和拦截器Interceptor 结合到一起，就构成了一个新的类InterceptorAndDynamicMethodMatcher ：

/**
 * Internal framework class, combining a MethodInterceptor instance
 * with a MethodMatcher for use as an element in the advisor chain.
 *
 * @author Rod Johnson
 */
class InterceptorAndDynamicMethodMatcher {

	final MethodInterceptor interceptor;

	final MethodMatcher methodMatcher;

	public InterceptorAndDynamicMethodMatcher(MethodInterceptor interceptor, MethodMatcher methodMatcher) {
		this.interceptor = interceptor;
		this.methodMatcher = methodMatcher;
	}

}

我们再将上述的包含整个拦截器执行链逻辑的ReflectiveMethodInvocation实现的核心代码在过一遍：

	@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);
		//起到一定的过滤作用，如果不匹配，则直接skip
                if (interceptorOrInterceptionAdvice instanceof InterceptorAndDynamicMethodMatcher) {
			// Evaluate dynamic method matcher here: static part will already have
			// been evaluated and found to match.
			InterceptorAndDynamicMethodMatcher dm =
					(InterceptorAndDynamicMethodMatcher) interceptorOrInterceptionAdvice;
			//满足匹配规则，则拦截器Advice生效
                        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.
                                //拦截器尚未生效，直接skip
                                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);
		}
	}

实战：

我们现在实现一个PointcutAdisor，PointcutAdvisor表示拥有某个Pointcut的Advisor。

package org.luanlouis.meditations.thinkinginspring.aop;

import org.aopalliance.aop.Advice;
import org.springframework.aop.Pointcut;
import org.springframework.aop.PointcutAdvisor;

/**
 * 实现一个PointcutAdvisor，通过提供的Pointcut,对Advice的执行进行过滤
 * Created by louis on 2016/4/16.
 */
public class FilteredAdvisor implements PointcutAdvisor {

    private Pointcut pointcut;
    private Advice advice;

    public FilteredAdvisor(Pointcut pointcut, Advice advice) {
        this.pointcut = pointcut;
        this.advice = advice;
    }

    /**
     * Get the Pointcut that drives this advisor.
     */
    @Override
    public Pointcut getPointcut() {
        return pointcut;
    }

    @Override
    public Advice getAdvice() {
        return advice;
    }

    @Override
    public boolean isPerInstance() {
        return false;
    }
}

package org.luanlouis.meditations.thinkinginspring.aop;

import org.aopalliance.aop.Advice;
import org.springframework.aop.aspectj.AspectJExpressionPointcut;
import org.springframework.aop.framework.ProxyFactoryBean;

/**
 * 通过ProxyFactoryBean 手动创建 代理对象
 * Created by louis on 2016/4/14.
 */
public class App {

    public static void main(String[] args) throws Exception {

        //1.针对不同的时期类型，提供不同的Advice
        Advice beforeAdvice = new TicketServiceBeforeAdvice();
        Advice afterReturningAdvice = new TicketServiceAfterReturningAdvice();
        Advice aroundAdvice = new TicketServiceAroundAdvice();
        Advice throwsAdvice = new TicketServiceThrowsAdvice();

        RailwayStation railwayStation = new RailwayStation();

        //2.创建ProxyFactoryBean,用以创建指定对象的Proxy对象
        ProxyFactoryBean proxyFactoryBean = new ProxyFactoryBean();
       //3.设置Proxy的接口
        proxyFactoryBean.setInterfaces(TicketService.class);
        //4. 设置RealSubject
        proxyFactoryBean.setTarget(railwayStation);
        //5.使用JDK基于接口实现机制的动态代理生成Proxy代理对象，如果想使用CGLIB，需要将这个flag设置成true
        proxyFactoryBean.setProxyTargetClass(true);

        //5. 添加不同的Advice

        proxyFactoryBean.addAdvice(afterReturningAdvice);
        proxyFactoryBean.addAdvice(aroundAdvice);
        proxyFactoryBean.addAdvice(throwsAdvice);
        //proxyFactoryBean.addAdvice(beforeAdvice);
        proxyFactoryBean.setProxyTargetClass(false);

        //手动创建一个pointcut,专门拦截sellTicket方法
        AspectJExpressionPointcut pointcut = new AspectJExpressionPointcut();
        pointcut.setExpression("execution( * sellTicket(..))");
        //传入创建的beforeAdvice和pointcut
        FilteredAdvisor sellBeforeAdvior = new FilteredAdvisor(pointcut,beforeAdvice);
        //添加到FactoryBean中
        proxyFactoryBean.addAdvisor(sellBeforeAdvior);
        
        //通过ProxyFactoryBean生成
        TicketService ticketService = (TicketService) proxyFactoryBean.getObject();
        ticketService.sellTicket();
        System.out.println("---------------------------");
        ticketService.inquire();

    }


}

这个时候，你会看到输出：

从结果中你可以清晰地看到，我们可以对某一个Advisor(即Advice)添加一个pointcut限制，这样就可以针对指定的方法执行Advice了！本例中使用了PointcutAdvisor,实际上，带底层代码中，Spring会将PointcutAdvisor转换成InterceptorAndDynamicMethodMatcher 参与ReflectiveMethodInvocation关于拦截器链的执行逻辑：

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());
		boolean hasIntroductions = hasMatchingIntroductions(config, actualClass);
		AdvisorAdapterRegistry registry = GlobalAdvisorAdapterRegistry.getInstance();
                
		for (Advisor advisor : config.getAdvisors()) {
                                //PointcutAdvisor向 InterceptorAndDynamicMethodMatcher 的转换  
                               if (advisor instanceof PointcutAdvisor) {
				// Add it conditionally.
				PointcutAdvisor pointcutAdvisor = (PointcutAdvisor) advisor;
				if (config.isPreFiltered() || pointcutAdvisor.getPointcut().getClassFilter().matches(actualClass)) {
					MethodInterceptor[] interceptors = registry.getInterceptors(advisor);
					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;
	}

}

7、总结

            至此，你已经了解了Spring的AOP的精髓，以及Spring的整个工作机制。我个人认为,想要理解Spring AOP，你需要从ProxyFactoryBean 开始，逐步地分析整个代理的构建过程：

            1. 代理对象是怎么生成的(JDK or Cglib)

            2. Advice链(即拦截器链)的构造过程以及执行机制

            3. 如何在Advice上添加pointcut,并且这个pointcut是如何工作的(实际上起到的过滤作用)

     

           最后再讲一下性能问题，如上面描述的，Spring创建Proxy的过程逻辑虽然很清晰，但是你也看到，对于我们每一个方法调用，都会经过非常复杂的层层Advice拦截判断，是否需要拦截处理，这个开销是非常大的。记得Spring的documentation介绍，如果使用Spring的AOP，对项目而言会造成10%的性能消耗，So，用AOP之前要仔细考虑一下性能问题~~~~~

            

作者的话

     本文使用的源码，已经托管到Github上，读者可以自行clone查看测验~

      源码地址：https://github.com/LuanLouis/thinking-in-spring.git ,请fetch branch : aop-principle   分支~

本文关于Spring AOP的设计原理仅是本人个人的见解和看法，如有任何疑问和错误，请不吝指出，敬请赐教，共同进步！