《Spring設計思想》AOP實現原理（基於JDK和基於CGLIB）

0、前言

     在上篇文章《Spring設計思想》AOP設計基本原理 中闡述了Spring AOP 的基本原理以及基本機制，本文將深入源碼，詳細闡述整個Spring AOP實現的整個過程。

    

1、Spring內部創建代理對象的過程

            在Spring的底層，如果我們配置了代理模式，Spring會爲每一個Bean創建一個對應的ProxyFactoryBean的FactoryBean來創建某個對象的代理對象。

            假定我們現在有一個接口TicketService及其實現類RailwayStation，我們打算創建一個代理類，在執行TicketService的方法時的各個階段，插入對應的業務代碼。

package org.luanlouis.meditations.thinkinginspring.aop;

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

    //售票
    public void sellTicket();

    //問詢
    public void inquire();

    //退票
    public void withdraw();
}

package org.luanlouis.meditations.thinkinginspring.aop;

/**
 * RailwayStation 實現 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("問詢.............");
    }

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

package org.luanlouis.meditations.thinkinginspring.aop;

import org.springframework.aop.MethodBeforeAdvice;

import java.lang.reflect.Method;

/**
 * 執行RealSubject對象的方法之前的處理意見
 * 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: 歡迎光臨代售點....");
    }
}

package org.luanlouis.meditations.thinkinginspring.aop;

import org.springframework.aop.AfterReturningAdvice;

import java.lang.reflect.Method;

/**
 * 返回結果時後的處理意見
 * 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：本次服務已結束....");
    }
}

package org.luanlouis.meditations.thinkinginspring.aop;

import org.springframework.aop.ThrowsAdvice;

import java.lang.reflect.Method;

/**
 * 拋出異常時的處理意見
 * 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("調用過程出錯啦！！！！！");
    }

} 

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;
    }
}

               現在，我們來手動使用ProxyFactoryBean來創建Proxy對象，並將相應的幾種不同的Advice加入這個proxy對應的各個執行階段中：

package org.luanlouis.meditations.thinkinginspring.aop;

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

/**
 * 通過ProxyFactoryBean 手動創建 代理對象
 * Created by louis on 2016/4/14.
 */
public class App {

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

        //1.針對不同的時期類型，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.創建ProxyFactoryBean,用以創建指定對象的Proxy對象
        ProxyFactoryBean proxyFactoryBean = new ProxyFactoryBean();
       //3.設置Proxy的接口
        proxyFactoryBean.setInterfaces(TicketService.class);
        //4. 設置RealSubject
        proxyFactoryBean.setTarget(railwayStation);
        //5.使用JDK基於接口實現機制的動態代理生成Proxy代理對象，如果想使用CGLIB，需要將這個flag設置成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通過ProxyFactoryBean生成Proxy對象
        TicketService ticketService = (TicketService) proxyFactoryBean.getObject();
        ticketService.sellTicket();

    }


}

不出意外的話，你會得到如下的輸出結果：

你會看到，我們成功地創建了一個通過一個ProxyFactoryBean和 真實的實例對象創建出了對應的代理對象，並將各個Advice加入到proxy代理對象中。

你會發現，在調用RailwayStation的sellticket()之前，成功插入了BeforeAdivce邏輯，而調用RailwayStation的sellticket()之後，AfterReturning邏輯也成功插入了。

AroundAdvice也成功包裹了sellTicket()方法，只不過這個AroundAdvice發生的時機有點讓人感到迷惑。實際上，這個背後的執行邏輯隱藏了Spring AOP關於AOP的關於Advice調度最爲核心的算法機制，這個將在本文後面詳細闡述。

另外，本例中ProxyFactoryBean是通過JDK的針對接口的動態代理模式生成代理對象的，具體機制，請看下面關於ProxyFactoryBean的介紹。

2、Spring AOP的核心---ProxyFactoryBean

          上面我們通過了純手動使用ProxyFactoryBean實現了AOP的功能。現在來分析一下上面的代碼：我們爲ProxyFactoryBean提供瞭如下信息：

1). Proxy應該感興趣的Adivce列表；

2). 真正的實例對象引用ticketService;

3).告訴ProxyFactoryBean使用基於接口實現的JDK動態代理機制實現proxy: 

4). Proxy應該具備的Interface接口：TicketService;

根據這些信息，ProxyFactoryBean就能給我們提供我們想要的Proxy對象了！那麼，ProxyFactoryBean幫我們做了什麼？

              Spring 使用工廠Bean模式創建每一個Proxy，對應每一個不同的Class類型，在Spring中都會有一個相對應的ProxyFactoryBean. 以下是ProxyFactoryBean的類圖。

如上所示，對於生成Proxy的工廠Bean而言，它要知道對其感興趣的Advice信息，而這類的信息，被維護到Advised中。Advised可以根據特定的類名和方法名返回對應的AdviceChain，用以表示需要執行的Advice串。

3、基於JDK面向接口的動態代理JdkDynamicAopProxy生成代理對象

JdkDynamicAopProxy類實現了AopProxy，能夠返回Proxy，並且，其自身也實現了InvocationHandler角色。也就是說，當我們使用proxy時，我們對proxy對象調用的方法，都最終被轉到這個類的invoke()方法中。

final class JdkDynamicAopProxy implements AopProxy, InvocationHandler, Serializable {
        //省略若干...
	/** Proxy的配置信息，這裏主要提供Advisor列表，並用於返回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());
	}
        //返回代理實例對象
	@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);
                //這裏的InvocationHandler設置成了當前實例對象，即對這個proxy調用的任何方法，都會調用這個類的invoke()方法
                //這裏的invoke方法被調用，動態查找Advice列表，組成ReflectMethodInvocation
		return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
	}
	/**
	 * 對當前proxy調用其上的任何方法，都將轉到這個方法上
         * 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.獲取當前調用方法的攔截鏈
			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.
                        //如果沒有攔截鏈，則直接調用Joinpoint連接點的方法。
			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...
                                //根據給定的攔截鏈和方法調用信息，創建新的MethodInvocation對象，整個攔截鏈的工作邏輯都在這個ReflectiveMethodInvocation裏 
				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、基於Cglib子類繼承方式的動態代理CglibAopProxy生成代理對象

基於Cglib子類繼承方式的動態代理CglibAopProxy生成代理對象：

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、各種Advice是的執行順序是如何和方法調用進行結合的？

JdkDynamicAopProxy 和CglibAopProxy只是創建代理方式的兩種方式而已，實際上我們爲方法調用添加的各種Advice的執行邏輯都是統一的。在Spring的底層，會把我們定義的各個Adivce分別 包裹成一個 MethodInterceptor,這些Advice按照加入Advised順序，構成一個AdivseChain.

比如我們上述的代碼：

        //5. 添加不同的Advice

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

當我們調用 ticketService.sellTicket()時，Spring會把這個方法調用轉換成一個MethodInvocation對象，然後結合上述的我們添加的各種Advice,組成一個ReflectiveMethodInvocation:

 各種Advice本質而言是一個方法調用攔截器，現在讓我們看看各個Advice攔截器都幹了什麼？

/**
 * 包裹MethodBeforeAdvice的方法攔截器
 * 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 {
		//在調用方法之前，先執行BeforeAdvice
		this.advice.before(mi.getMethod(), mi.getArguments(), mi.getThis() );
		return mi.proceed();
	}

}

/**
 * 包裹AfterReturningAdvice的方法攔截器
 * 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 {
		//先調用invocation
		Object retVal = mi.proceed();
		//調用成功後，調用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定義的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，先執行代碼，捕獲異常
		try {
			return mi.proceed();
		}
		catch (Throwable ex) {
			//獲取異常處理方法
			Method handlerMethod = getExceptionHandler(ex);
			//調用異常處理方法
			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();
		}
	}

}

關於AroundAdivce,其本身就是一個MethodInterceptor，所以不需要額外做轉換了。

細心的你會發現，在攔截器串中，每個攔截器最後都會調用MethodInvocation的proceed()方法。如果按照簡單的攔截器的執行串來執行的話，MethodInvocation的proceed()方法至少要執行N次(N表示攔截器Interceptor的個數)，因爲每個攔截器都會調用一次proceed()方法。更直觀地講，比如我們調用了ticketService.sellTicket()方法，那麼，按照這個邏輯，我們會打印出四條記錄：

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

這樣我們肯定不是我們需要的結果！！！！因爲按照我們的理解，只應該有一條"售票............"纔對。真實的Spring的方法調用過程能夠控制這個邏輯按照我們的思路執行，Spring將這個整個方法調用過程連同若干個Advice組成的攔截器鏈組合成ReflectiveMethodInvocation對象，讓我們來看看這一執行邏輯是怎麼控制的：

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對象
		this.target = target;//真實的realSubject對象
		this.targetClass = targetClass;//被代理的類類型
		this.method = BridgeMethodResolver.findBridgedMethod(method);//方法引用
		this.arguments = AopProxyUtils.adaptArgumentsIfNecessary(method, arguments);//調用參數
		this.interceptorsAndDynamicMethodMatchers = interceptorsAndDynamicMethodMatchers;//Advice攔截器鏈
	}


	@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 {
		//	沒有攔截器，則直接調用Joinpoint上的method，即直接調用MethodInvocation We start with an index of -1 and increment early.
		if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) {
			return invokeJoinpoint();
		}
                // 取得第攔截器鏈上第N個攔截器 
		Object interceptorOrInterceptionAdvice =
				this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex);
		//PointcutInterceptor會走這個邏輯
                if (interceptorOrInterceptionAdvice instanceof InterceptorAndDynamicMethodMatcher) {
			// Evaluate dynamic method matcher here: static part will already have
			// been evaluated and found to match.
			InterceptorAndDynamicMethodMatcher dm =
					(InterceptorAndDynamicMethodMatcher) interceptorOrInterceptionAdvice;
			//當前攔截器是符合攔截規則，每個攔截器可以定義是否特定的類和方法名是否符合攔截規則
                        //實際上PointCut定義的方法簽名最後會轉換成這個MethodMatcher，並置於攔截器中
                        if (dm.methodMatcher.matches(this.method, this.targetClass, this.arguments)) {
			     //符合攔截規則，調用攔截器invoke()	
                             return dm.interceptor.invoke(this);
			}
			else {
				// Dynamic matching failed.
				// Skip this interceptor and invoke the next in the chain.
                                // 當前方法不需要攔截器操作，則直接往前推進
                                return proceed();
			}
		}
		else {
			// It's an interceptor, so we just invoke it: The pointcut will have
			// been evaluated statically before this object was constructed.
                        //直接調用攔截器，
                        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);
	}

上述的代碼比較冗雜，解釋起來比較繁瑣，請看下面一張圖，你就知道這段代碼的思路了：

實例分析

根據上面的執行鏈上的邏輯，我們將我們上面舉的例子的輸出結果在整理一下：

Advice攔截器的添加順序:

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

第一個攔截器：AfterReturningAdvice

第一個添加的是afterReturningAdivce,它所處的位置是第一個攔截器，執行的操作就是：

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

也就是說，先完成MethodInvocation的proceed()方法再執行相應的advice；而調用了mi.proceed()方法，導致了當前的調用鏈後移，進行和後續的操作，也就是說，AfterReturningAdvice只能等到整個攔截器鏈上所有執行完畢後纔會生效，所以：AFTER_RETURNING:本次服務已結束.... 這句話排在了最後：

第二個攔截器：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;
    }

現在執行到了第二個攔截器，首先輸出了"AROUND_ADVICE:BEGIN......"，接着調用Invocation.proceed(),等到剩餘的執行完後，再輸出"AROUND_ADVICE:END....."：

第三個攔截器：ThrowsAdvice:

ThrowsAdvice攔截器的處理模式是：

	@Override
	public Object invoke(MethodInvocation mi) throws Throwable {
		try {
		       //先執行invocation.proceed();	
                       return mi.proceed();
		}
		catch (Throwable ex) {
                       //捕捉錯誤，調用afterThrowing()方法
                        Method handlerMethod = getExceptionHandler(ex);
			if (handlerMethod != null) {
				invokeHandlerMethod(mi, ex, handlerMethod);
			}
			throw ex;
		}
	}

上述的邏輯是，先執行Invocation.proceed();如果這個過程中拋出異常，則調用ThrowsAdvice。

第四個攔截器:BeforeAdvice:

這個攔截器的工作邏輯如下：

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

綜上所有的攔截器過程，我們就能理解，爲什麼我們剛開始的輸出爲什麼是下面這樣了：

6、PointCut與Advice的結合------Adivce的條件執行

上面我們提供了幾個Adivce，你會發現，這些Advice是無條件地加入了我們創建的對象中。無論調用Target的任何方法，這些Advice都會被觸發到。

那麼，我們可否告訴Advice，只讓它對特定的方法或特定類起作用呢？ 這個實際上是要求我們添加一個過濾器，如果滿足條件，則Advice生效，否則無效。Spring將這個過濾器抽象成如下的接口：

public interface MethodMatcher {

	/**
	 * 提供方法簽名和所屬的Class類型，判斷是否支持 
         * 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;

}

將這個匹配器MethodMatcher和攔截器Interceptor 結合到一起，就構成了一個新的類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;
	}

}

我們再將上述的包含整個攔截器執行鏈邏輯的ReflectiveMethodInvocation實現的核心代碼在過一遍：

	@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);
		//起到一定的過濾作用，如果不匹配，則直接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;
			//滿足匹配規則，則攔截器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.
                                //攔截器尚未生效，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);
		}
	}

實戰：

我們現在實現一個PointcutAdisor，PointcutAdvisor表示擁有某個Pointcut的Advisor。

package org.luanlouis.meditations.thinkinginspring.aop;

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

/**
 * 實現一個PointcutAdvisor，通過提供的Pointcut,對Advice的執行進行過濾
 * 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;

/**
 * 通過ProxyFactoryBean 手動創建 代理對象
 * Created by louis on 2016/4/14.
 */
public class App {

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

        //1.針對不同的時期類型，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.創建ProxyFactoryBean,用以創建指定對象的Proxy對象
        ProxyFactoryBean proxyFactoryBean = new ProxyFactoryBean();
       //3.設置Proxy的接口
        proxyFactoryBean.setInterfaces(TicketService.class);
        //4. 設置RealSubject
        proxyFactoryBean.setTarget(railwayStation);
        //5.使用JDK基於接口實現機制的動態代理生成Proxy代理對象，如果想使用CGLIB，需要將這個flag設置成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);

        //手動創建一個pointcut,專門攔截sellTicket方法
        AspectJExpressionPointcut pointcut = new AspectJExpressionPointcut();
        pointcut.setExpression("execution( * sellTicket(..))");
        //傳入創建的beforeAdvice和pointcut
        FilteredAdvisor sellBeforeAdvior = new FilteredAdvisor(pointcut,beforeAdvice);
        //添加到FactoryBean中
        proxyFactoryBean.addAdvisor(sellBeforeAdvior);
        
        //通過ProxyFactoryBean生成
        TicketService ticketService = (TicketService) proxyFactoryBean.getObject();
        ticketService.sellTicket();
        System.out.println("---------------------------");
        ticketService.inquire();

    }


}

這個時候，你會看到輸出：

從結果中你可以清晰地看到，我們可以對某一個Advisor(即Advice)添加一個pointcut限制，這樣就可以針對指定的方法執行Advice了！本例中使用了PointcutAdvisor,實際上，帶底層代碼中，Spring會將PointcutAdvisor轉換成InterceptorAndDynamicMethodMatcher 參與ReflectiveMethodInvocation關於攔截器鏈的執行邏輯：

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 的轉換  
                               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、總結

            至此，你已經瞭解了Spring的AOP的精髓，以及Spring的整個工作機制。我個人認爲,想要理解Spring AOP，你需要從ProxyFactoryBean 開始，逐步地分析整個代理的構建過程：

            1. 代理對象是怎麼生成的(JDK or Cglib)

            2. Advice鏈(即攔截器鏈)的構造過程以及執行機制

            3. 如何在Advice上添加pointcut,並且這個pointcut是如何工作的(實際上起到的過濾作用)

     

           最後再講一下性能問題，如上面描述的，Spring創建Proxy的過程邏輯雖然很清晰，但是你也看到，對於我們每一個方法調用，都會經過非常複雜的層層Advice攔截判斷，是否需要攔截處理，這個開銷是非常大的。記得Spring的documentation介紹，如果使用Spring的AOP，對項目而言會造成10%的性能消耗，So，用AOP之前要仔細考慮一下性能問題~~~~~

            

作者的話

     本文使用的源碼，已經託管到Github上，讀者可以自行clone查看測驗~

      源碼地址：https://github.com/LuanLouis/thinking-in-spring.git ,請fetch branch : aop-principle   分支~

本文關於Spring AOP的設計原理僅是本人個人的見解和看法，如有任何疑問和錯誤，請不吝指出，敬請賜教，共同進步！