Spring中AOP的學習

1、cglib的學習，cglib是靠繼承關係來實現代理的目的，即具體代碼如下：

Java代碼

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;
}
}

 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，主要靠實現接口來實現代理的目的，即具體代碼如下：

Java代碼

public class AOPHandler implements InvocationHandler {
private static Log logger = LogFactory.getLog(AOPHandler.class);
private List interceptors = null;
private Object originalObject;
/**
* 返回動態代理實例
*
* @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，加載對應的Interceptor，並進行
* 預處理(before)、後處理(after)以及異常處理（exceptionThrow）過程
*/
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;
}
/**
* 加載Interceptor
*
* @return
*/
private synchronized List getIntercetors() {
if (null == interceptors) {
interceptors = new ArrayList();
//Todo：讀取配置，加載Interceptor實例
interceptors.add(new MyInterceptor());
}
return interceptors;
}
/**
* 執行預處理方法
*
* @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);
}
}
/**
* 執行後處理方法
*
* @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);
}
}
/**
* 執行異常處理方法
*
* @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 AOPHandler implements InvocationHandler {
	private static Log logger = LogFactory.getLog(AOPHandler.class);
	private List interceptors = null;
	private Object originalObject;
	/**
	 * 返回動態代理實例
	 * 
	 * @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，加載對應的Interceptor，並進行
	 * 預處理(before)、後處理(after)以及異常處理（exceptionThrow）過程
	 */
	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;
	}
	/**
	 * 加載Interceptor
	 * 
	 * @return
	 */
	private synchronized List getIntercetors() {
		if (null == interceptors) {
			interceptors = new ArrayList();
			//Todo：讀取配置，加載Interceptor實例
			interceptors.add(new MyInterceptor());
		}
		return interceptors;
	}
	/**
	 * 執行預處理方法
	 * 
	 * @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);
		}
	}
	/**
	 * 執行後處理方法
	 * 
	 * @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);
		}
	}
	/**
	 * 執行異常處理方法
	 * 
	 * @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);
		}
	}
}

Java代碼

public class AOPFactory {
static AOPHandler txHandler ;
private static Log logger = LogFactory.getLog(AOPFactory.class);
/**
* 根據類名創建類實例
*
* @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);
}
}
/**
* 根據傳入的類名，返回AOP代理對象
*
* @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 class AOPFactory {
	static AOPHandler txHandler ;
	private static Log logger = LogFactory.getLog(AOPFactory.class);
	/**
	 * 根據類名創建類實例
	 * 
	 * @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);
		}
	}
	/**
	 * 根據傳入的類名，返回AOP代理對象
	 * 
	 * @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;
	}
}

Java代碼

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

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

Java代碼

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");
}
}

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的實現。剖析Spring中的cglig和proxy。
Spring中的核心模塊爲：bean和aop；其中bean模塊對aop提供了支持。

Java代碼

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 {
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;
	}
}

Java代碼

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 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;
	}
}

Java代碼

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;
}
}

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;
	}
}

Java代碼

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);
}
}

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);
	}
}

Java代碼

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);
}
}
}

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