/*
 * Copyright 2002-2012 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.aop.framework;

import java.io.Serializable;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.List;

import org.aopalliance.intercept.MethodInvocation;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.aop.AopInvocationException;
import org.springframework.aop.RawTargetAccess;
import org.springframework.aop.TargetSource;
import org.springframework.aop.support.AopUtils;
import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;

/**
 * JDK-based {@link AopProxy} implementation for the Spring AOP framework,
 * based on JDK {@link java.lang.reflect.Proxy dynamic proxies}.
 *
 * <p>Creates a dynamic proxy, implementing the interfaces exposed by
 * the AopProxy. Dynamic proxies <i>cannot</i> be used to proxy methods
 * defined in classes, rather than interfaces.
 *
 * <p>Objects of this type should be obtained through proxy factories,
 * configured by an {@link AdvisedSupport} class. This class is internal
 * to Spring's AOP framework and need not be used directly by client code.
 *
 * <p>Proxies created using this class will be thread-safe if the
 * underlying (target) class is thread-safe.
 *
 * <p>Proxies are serializable so long as all Advisors (including Advices
 * and Pointcuts) and the TargetSource are serializable.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @author Rob Harrop
 * @author Dave Syer
 * @see java.lang.reflect.Proxy
 * @see AdvisedSupport
 * @see ProxyFactory
 */
final class JdkDynamicAopProxy implements AopProxy, InvocationHandler, Serializable {

	/** use serialVersionUID from Spring 1.2 for interoperability */
	private static final long serialVersionUID = 5531744639992436476L;


	/*
	 * NOTE: We could avoid the code duplication between this class and the CGLIB
	 * proxies by refactoring "invoke" into a template method. However, this approach
	 * adds at least 10% performance overhead versus a copy-paste solution, so we sacrifice
	 * elegance for performance. (We have a good test suite to ensure that the different
	 * proxies behave the same :-)
	 * This way, we can also more easily take advantage of minor optimizations in each class.
	 */

	/** We use a static Log to avoid serialization issues */
	private static Log logger = LogFactory.getLog(JdkDynamicAopProxy.class);

	/** Config used to configure this proxy */
	private final AdvisedSupport advised;

	/**
	 * Is the {@link #equals} method defined on the proxied interfaces?
	 */
	private boolean equalsDefined;

	/**
	 * Is the {@link #hashCode} method defined on the proxied interfaces?
	 */
	private boolean hashCodeDefined;


	/**
	 * Construct a new JdkDynamicAopProxy for the given AOP configuration.
	 * @param config the AOP configuration as AdvisedSupport object
	 * @throws AopConfigException if the config is invalid. We try to throw an informative
	 * exception in this case, rather than let a mysterious failure happen later.
	 */
	public JdkDynamicAopProxy(AdvisedSupport config) throws AopConfigException {
		Assert.notNull(config, "AdvisedSupport must not be null");
		if (config.getAdvisors().length == 0 && config.getTargetSource() == AdvisedSupport.EMPTY_TARGET_SOURCE) {
			throw new AopConfigException("No advisors and no TargetSource specified");
		}
		this.advised = config;
	}


	public Object getProxy() {
		return getProxy(ClassUtils.getDefaultClassLoader());
	}

	/**
	 * <ol>
	 * <li>获取代理类要实现的接口,除了 Advised 对象中配置的,还会加上 SpringProxy, Advised(opaque=false)
	 * <li>检查上面得到的接口中有没有定义 equals 或者 hashcode 的接口
	 * <li>调用 Proxy.newProxyInstance 创建代理对象
	 * </ol>
	 */
	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);
		return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
	}

	/**
	 * Finds any {@link #equals} or {@link #hashCode} method that may be defined
	 * on the supplied set of interfaces.
	 * @param proxiedInterfaces the interfaces to introspect
	 */
	private void findDefinedEqualsAndHashCodeMethods(Class[] proxiedInterfaces) {
		for (Class proxiedInterface : proxiedInterfaces) {
			Method[] methods = proxiedInterface.getDeclaredMethods();
			for (Method method : methods) {
				if (AopUtils.isEqualsMethod(method)) {
					this.equalsDefined = true;
				}
				if (AopUtils.isHashCodeMethod(method)) {
					this.hashCodeDefined = true;
				}
				if (this.equalsDefined && this.hashCodeDefined) {
					return;
				}
			}
		}
	}


	/**
	 * Implementation of {@code InvocationHandler.invoke}.
	 * <p>Callers will see exactly the exception thrown by the target,
	 * unless a hook method throws an exception.
	 */
	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 {
			//eqauls()方法，具目标对象未实现此方法
			if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) {
				// The target does not implement the equals(Object) method itself.
				return equals(args[0]);
			}
			//hashCode()方法，具目标对象未实现此方法
			if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)) {
				// The target does not implement the hashCode() method itself.
				return hashCode();
			}
			//Advised 接口或者其父接口中定义的方法,直接反射调用,不应用通知
			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.
			//获得目标对象的类
			target = targetSource.getTarget();
			if (target != null) {
				targetClass = target.getClass();
			}

			//获取可以应用到此方法上的 Interceptor 列表
			// 给环绕通知做准备
			// Get the interception chain for this method.
			List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);

			// Check whether we have any advice. If we don't, we can fallback on direct
			// reflective invocation of the target, and avoid creating a MethodInvocation.
			//如果没有可以应用到此方法的通知(Interceptor)，此直接反射调用 method.invoke(target, args)
			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.
				retVal = AopUtils.invokeJoinpointUsingReflection(target, method, args);
			}
			else {
				// We need to create a method invocation...
				//创建 MethodInvocation
				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);
			}
		}
	}


	/**
	 * Equality means interfaces, advisors and TargetSource are equal.
	 * <p>The compared object may be a JdkDynamicAopProxy instance itself
	 * or a dynamic proxy wrapping a JdkDynamicAopProxy instance.
	 */
	@Override
	public boolean equals(Object other) {
		if (other == this) {
			return true;
		}
		if (other == null) {
			return false;
		}

		JdkDynamicAopProxy otherProxy;
		if (other instanceof JdkDynamicAopProxy) {
			otherProxy = (JdkDynamicAopProxy) other;
		}
		else if (Proxy.isProxyClass(other.getClass())) {
			InvocationHandler ih = Proxy.getInvocationHandler(other);
			if (!(ih instanceof JdkDynamicAopProxy)) {
				return false;
			}
			otherProxy = (JdkDynamicAopProxy) ih;
		}
		else {
			// Not a valid comparison...
			return false;
		}

		// If we get here, otherProxy is the other AopProxy.
		return AopProxyUtils.equalsInProxy(this.advised, otherProxy.advised);
	}

	/**
	 * Proxy uses the hash code of the TargetSource.
	 */
	@Override
	public int hashCode() {
		return JdkDynamicAopProxy.class.hashCode() * 13 + this.advised.getTargetSource().hashCode();
	}

}
