Spring中AOP的学习

今天对Proxy和cglib的原理进行了一些学习，主要是参考网上找来的资料：
准备工作，对cglig和proxy代理进行相关的学习。

1、cglib的学习，cglib是靠继承关系来实现代理的目的，即具体代码如下：

 public class AOPInstrumenter implements MethodInterceptor {
	private static Log logger = LogFactory.getLog(AOPInstrumenter.class);
	private Enhancer enhancer = new Enhancer();
	public Object getInstrumentedClass(Class clz) {
		enhancer.setSuperclass(clz);
		enhancer.setCallback(this);
		return enhancer.create();
	}
	public Object intercept(Object o, Method method, Object[] methodParameters,MethodProxy methodProxy) throws Throwable {
		logger.debug("Before Method =>" + method.getName());
		Object result = methodProxy.invokeSuper(o, methodParameters);
		logger.debug("After Method =>" + method.getName());
		return result;
	}
}

2、proxy代理，主要靠实现接口来实现代理的目的，即具体代码如下：

public class AOPHandler implements InvocationHandler {
	private static Log logger = LogFactory.getLog(AOPHandler.class);
	private List interceptors = null;
	private Object originalObject;
	/**
	 * 返回动态代理实例
	 * 
	 * @param obj
	 * @return
	 */
	public Object bind(Object obj) {
		this.originalObject = obj;
		return Proxy.newProxyInstance(obj.getClass().getClassLoader(), obj.getClass().getInterfaces(), this);
	}
	/**
	 * 在Invoke方法中，加载对应的Interceptor，并进行
	 * 预处理(before)、后处理(after)以及异常处理（exceptionThrow）过程
	 */
	public Object invoke(Object proxy, Method method, Object[] args)throws Throwable {
		Object result = null;
		Throwable ex = null;
		InvocationInfo invInfo = new InvocationInfo(proxy, method, args,result, ex);
		logger.debug("Invoking Before Intercetpors!");
		invokeInterceptorsBefore(invInfo);
		try {
			logger.debug("Invoking Proxy Method!");
			result = method.invoke(originalObject, args);
			invInfo.setResult(result);
			logger.debug("Invoking After Method!");
			invokeInterceptorsAfter(invInfo);
		} catch (Throwable tr) {
			invInfo.setException(tr);
			logger.debug("Invoking exceptionThrow Method!");
			invokeInterceptorsExceptionThrow(invInfo);
			throw new AOPRuntimeException(tr);
		}
		return result;
	}
	/**
	 * 加载Interceptor
	 * 
	 * @return
	 */
	private synchronized List getIntercetors() {
		if (null == interceptors) {
			interceptors = new ArrayList();
			//Todo：读取配置，加载Interceptor实例
			interceptors.add(new MyInterceptor());
		}
		return interceptors;
	}
	/**
	 * 执行预处理方法
	 * 
	 * @param invInfo
	 */
	private void invokeInterceptorsBefore(InvocationInfo invInfo) {
		List interceptors = getIntercetors();
		int len = interceptors.size();
		for (int i = 0; i < len; i++) {
			((Interceptor) interceptors.get(i)).before(invInfo);
		}
	}
	/**
	 * 执行后处理方法
	 * 
	 * @param invInfo
	 */
	private void invokeInterceptorsAfter(InvocationInfo invInfo) {
		List interceptors = getIntercetors();
		int len = interceptors.size();
		for (int i = len - 1; i >= 0; i--) {
			((Interceptor) interceptors.get(i)).after(invInfo);
		}
	}
	/**
	 * 执行异常处理方法
	 * 
	 * @param invInfo
	 */
	private void invokeInterceptorsExceptionThrow(InvocationInfo invInfo) {
		List interceptors = getIntercetors();
		int len = interceptors.size();
		for (int i = len - 1; i >= 0; i--) {
			((Interceptor) interceptors.get(i)).exceptionThrow(invInfo);
		}
	}
}

public class AOPFactory {
	static AOPHandler txHandler ;
	private static Log logger = LogFactory.getLog(AOPFactory.class);
	/**
	 * 根据类名创建类实例
	 * 
	 * @param clzName
	 * @return
	 * @throws ClassNotFoundException
	 */
	public static Object getClassInstance(String clzName) {
		Class cls;
		try {
			cls = Class.forName(clzName);
			return (Object) cls.newInstance();
		} catch (ClassNotFoundException e) {
			logger.debug(e);
			throw new AOPRuntimeException(e);
		} catch (InstantiationException e) {
			logger.debug(e);
			throw new AOPRuntimeException(e);
		} catch (IllegalAccessException e) {
			logger.debug(e);
			throw new AOPRuntimeException(e);
		}
	}
	/**
	 * 根据传入的类名，返回AOP代理对象
	 * 
	 * @param clzName
	 * @return
	 */
	public static Object getAOPProxyedObject(String clzName) {
		txHandler = new AOPHandler();
		Object obj = getClassInstance(clzName);
		return txHandler.bind(obj);
	}

	/**
	 * @return Returns the txHandler.
	 */
	public static AOPHandler getTxHandler() {
		return txHandler;
	}
}

public interface Interceptor {
	public void before(InvocationInfo invInfo);
	public void after(InvocationInfo invInfo);
	public void exceptionThrow(InvocationInfo invInfo);
}

public class MyInterceptor implements Interceptor {
	private static Log logger = LogFactory.getLog(MyInterceptor.class);
	public void before(InvocationInfo invInfo) {
		logger.debug("Pre-processing");
	}
	public void after(InvocationInfo invInfo) {
		logger.debug("Post-processing");
	}
	public void exceptionThrow(InvocationInfo invInfo) {
		logger.debug("Exception-processing");
	}
}

3、Spring中AOP的实现。剖析Spring中的cglig和proxy。
Spring中的核心模块为：bean和aop；其中bean模块对aop提供了支持。

public abstract class AbstractBeanFactory implements ConfigurableBeanFactory {
public Object getBean(String name, Class requiredType, Object[] args) throws BeansException {
		String beanName = transformedBeanName(name);
		Object bean = null;

		// Eagerly check singleton cache for manually registered singletons.
		Object sharedInstance = null;
		synchronized (this.singletonCache) {
			sharedInstance = this.singletonCache.get(beanName);
		}
		if (sharedInstance != null) {
			if (sharedInstance == CURRENTLY_IN_CREATION) {
				throw new BeanCurrentlyInCreationException(beanName);
			}
			if (logger.isDebugEnabled()) {
				logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
			}
			bean = getObjectForSharedInstance(name, sharedInstance);		}

		else {
			// Check if bean definition exists in this factory.
			RootBeanDefinition mergedBeanDefinition = null;
			try {
				mergedBeanDefinition = getMergedBeanDefinition(beanName, false);
			}
			catch (NoSuchBeanDefinitionException ex) {
				// Not found -> check parent.
				if (this.parentBeanFactory instanceof AbstractBeanFactory) {
					// Delegation to parent with args only possible for AbstractBeanFactory.
					return ((AbstractBeanFactory) this.parentBeanFactory).getBean(name, requiredType, args);
				}
				else if (this.parentBeanFactory != null && args == null) {
					// No args -> delegate to standard getBean method.
					return this.parentBeanFactory.getBean(name, requiredType);
				}
				throw ex;
			}

			checkMergedBeanDefinition(mergedBeanDefinition, beanName, requiredType, args);

			// Create bean instance.
			if (mergedBeanDefinition.isSingleton()) {
				synchronized (this.singletonCache) {
					// re-check singleton cache within synchronized block
					sharedInstance = this.singletonCache.get(beanName);
					if (sharedInstance == null) {
						if (logger.isInfoEnabled()) {
							logger.info("Creating shared instance of singleton bean '" + beanName + "'");
						}
						this.singletonCache.put(beanName, CURRENTLY_IN_CREATION);
						try {
							sharedInstance = createBean(beanName, mergedBeanDefinition, args);
							this.singletonCache.put(beanName, sharedInstance);
						}
						catch (BeansException ex) {
							this.singletonCache.remove(beanName);
							throw ex;
						}
					}
				}
				bean = getObjectForSharedInstance(name, sharedInstance);
			}
			else {
				// It's a prototype -> create a new instance.
				bean = createBean(name, mergedBeanDefinition, args);
			}
		}

		// Check if required type matches the type of the actual bean instance.
		if (requiredType != null && !requiredType.isAssignableFrom(bean.getClass())) {
			throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
		}
		return bean;
	}
}

public abstract class AbstractBeanFactory implements ConfigurableBeanFactory {
	protected Object getObjectForSharedInstance(String name, Object beanInstance) throws BeansException {
		String beanName = transformedBeanName(name);

		// Don't let calling code try to dereference the
		// bean factory if the bean isn't a factory.
		if (isFactoryDereference(name) && !(beanInstance instanceof FactoryBean)) {
			throw new BeanIsNotAFactoryException(beanName, beanInstance.getClass());
		}

		// Now we have the bean instance, which may be a normal bean or a FactoryBean.
		// If it's a FactoryBean, we use it to create a bean instance, unless the
		// caller actually wants a reference to the factory.
		if (beanInstance instanceof FactoryBean) {
			if (!isFactoryDereference(name)) {
				// Return bean instance from factory.
				FactoryBean factory = (FactoryBean) beanInstance;
				if (logger.isDebugEnabled()) {
					logger.debug("Bean with name '" + beanName + "' is a factory bean");
				}
				try {
					beanInstance = factory.getObject();
				}
				catch (Exception ex) {
					throw new BeanCreationException(beanName, "FactoryBean threw exception on object creation", ex);
				}
				if (beanInstance == null) {
					throw new FactoryBeanNotInitializedException(
					    beanName, "FactoryBean returned null object: " +
							"probably not fully initialized (maybe due to circular bean reference)");
				}
			}
			else {
	 			// The user wants the factory itself.
				if (logger.isDebugEnabled()) {
					logger.debug("Calling code asked for FactoryBean instance for name '" + beanName + "'");
				}
			}
		}

		return beanInstance;
	}
}

public class ProxyFactoryBean extends AdvisedSupport
    implements FactoryBean, BeanFactoryAware, AdvisedSupportListener {
	public Object getObject() throws BeansException {
		return this.singleton ? getSingletonInstance() : newPrototypeInstance();
	}


	private Object getSingletonInstance() {
		if (this.singletonInstance == null) {
			super.setFrozen(this.freezeProxy);
			this.singletonInstance = createAopProxy().getProxy();
		}
		return this.singletonInstance;
	}
}

final class JdkDynamicAopProxy implements AopProxy, InvocationHandler, Serializable {
	public Object getProxy(ClassLoader classLoader) {
		if (logger.isDebugEnabled()) {
			Class targetClass = this.advised.getTargetSource().getTargetClass();
			logger.debug("Creating JDK dynamic proxy" +
					(targetClass != null ? " for [" + targetClass.getName() + "]" : ""));
		}
		Class[] proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised);
		return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
	}
}

public class Cglib2AopProxy implements AopProxy, Serializable {
	public Object getProxy(ClassLoader classLoader) {
		if (logger.isDebugEnabled()) {
			Class targetClass = this.advised.getTargetSource().getTargetClass();
			logger.debug("Creating CGLIB2 proxy" +
					(targetClass != null ? " for [" + targetClass.getName() + "]" : ""));
		}

		Enhancer enhancer = new Enhancer();
		try {
			Class rootClass = this.advised.getTargetSource().getTargetClass();

			if (AopUtils.isCglibProxyClass(rootClass)) {
				enhancer.setSuperclass(rootClass.getSuperclass());
			}
			else {
				enhancer.setSuperclass(rootClass);
			}

			enhancer.setCallbackFilter(new ProxyCallbackFilter(this.advised));
			enhancer.setStrategy(new UndeclaredThrowableStrategy(UndeclaredThrowableException.class));
			enhancer.setInterfaces(AopProxyUtils.completeProxiedInterfaces(this.advised));

			Callback[] callbacks = getCallbacks(rootClass);
			enhancer.setCallbacks(callbacks);

			if(CglibUtils.canSkipConstructorInterception()) {
				enhancer.setInterceptDuringConstruction(false);
			}
			
			Class[] types = new Class[callbacks.length];
			for (int x = 0; x < types.length; x++) {
				types[x] = callbacks[x].getClass();
			}
			enhancer.setCallbackTypes(types);

			// generate the proxy class and create a proxy instance
			Object proxy;
			if (this.constructorArgs != null) {
				proxy = enhancer.create(this.constructorArgTypes, this.constructorArgs);
			}
			else {
				proxy = enhancer.create();
			}

			return proxy;
		}
		catch (CodeGenerationException ex) {
			throw new AspectException("Couldn't generate CGLIB subclass of class '" +
					this.advised.getTargetSource().getTargetClass() + "': " +
					"Common causes of this problem include using a final class or a non-visible class",
					ex);
		}
		catch (IllegalArgumentException ex) {
			throw new AspectException("Couldn't generate CGLIB subclass of class '" +
					this.advised.getTargetSource().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 AspectException("Unexpected AOP exception", ex);
		}
	}
}