/*
 * Copyright 2002-2017 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
 *
 *      https://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.config;

import java.util.List;

import org.w3c.dom.Node;

import org.springframework.aop.framework.ProxyFactoryBean;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.config.BeanDefinitionHolder;
import org.springframework.beans.factory.support.AbstractBeanDefinition;
import org.springframework.beans.factory.support.BeanDefinitionReaderUtils;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.ManagedList;
import org.springframework.beans.factory.support.RootBeanDefinition;
import org.springframework.beans.factory.xml.BeanDefinitionDecorator;
import org.springframework.beans.factory.xml.ParserContext;
import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;
import org.springframework.util.StringUtils;

Base implementation for BeanDefinitionDecorators wishing to add an interceptor to the resulting bean. 
This base class controls the creation of the ProxyFactoryBean bean definition and wraps the original as an inner-bean definition for the target property of ProxyFactoryBean. 
Chaining is correctly handled, ensuring that only one ProxyFactoryBean definition is created. If a previous BeanDefinitionDecorator already created the ProxyFactoryBean then the interceptor is simply added to the existing definition. 
Subclasses have only to create the BeanDefinition to the interceptor that they wish to add. 
Author:
Rob Harrop, Juergen Hoeller
See Also:
MethodInterceptor
Since:
2.0/**
 * Base implementation for
 * {@link org.springframework.beans.factory.xml.BeanDefinitionDecorator BeanDefinitionDecorators}
 * wishing to add an {@link org.aopalliance.intercept.MethodInterceptor interceptor}
 * to the resulting bean.
 *
 * <p>This base class controls the creation of the {@link ProxyFactoryBean} bean definition
 * and wraps the original as an inner-bean definition for the {@code target} property
 * of {@link ProxyFactoryBean}.
 *
 * <p>Chaining is correctly handled, ensuring that only one {@link ProxyFactoryBean} definition
 * is created. If a previous {@link org.springframework.beans.factory.xml.BeanDefinitionDecorator}
 * already created the {@link org.springframework.aop.framework.ProxyFactoryBean} then the
 * interceptor is simply added to the existing definition.
 *
 * <p>Subclasses have only to create the {@code BeanDefinition} to the interceptor that
 * they wish to add.
 *
 * @author Rob Harrop
 * @author Juergen Hoeller
 * @since 2.0
 * @see org.aopalliance.intercept.MethodInterceptor
 */
public abstract class AbstractInterceptorDrivenBeanDefinitionDecorator implements BeanDefinitionDecorator {

	@Override
	public final BeanDefinitionHolder decorate(Node node, BeanDefinitionHolder definitionHolder, ParserContext parserContext) {
		BeanDefinitionRegistry registry = parserContext.getRegistry();

		// get the root bean name - will be the name of the generated proxy factory bean
		String existingBeanName = definitionHolder.getBeanName();
		BeanDefinition targetDefinition = definitionHolder.getBeanDefinition();
		BeanDefinitionHolder targetHolder = new BeanDefinitionHolder(targetDefinition, existingBeanName + ".TARGET");

		// delegate to subclass for interceptor definition
		BeanDefinition interceptorDefinition = createInterceptorDefinition(node);

		// generate name and register the interceptor
		String interceptorName = existingBeanName + '.' + getInterceptorNameSuffix(interceptorDefinition);
		BeanDefinitionReaderUtils.registerBeanDefinition(
				new BeanDefinitionHolder(interceptorDefinition, interceptorName), registry);

		BeanDefinitionHolder result = definitionHolder;

		if (!isProxyFactoryBeanDefinition(targetDefinition)) {
			// create the proxy definition
			RootBeanDefinition proxyDefinition = new RootBeanDefinition();
			// create proxy factory bean definition
			proxyDefinition.setBeanClass(ProxyFactoryBean.class);
			proxyDefinition.setScope(targetDefinition.getScope());
			proxyDefinition.setLazyInit(targetDefinition.isLazyInit());
			// set the target
			proxyDefinition.setDecoratedDefinition(targetHolder);
			proxyDefinition.getPropertyValues().add("target", targetHolder);
			// create the interceptor names list
			proxyDefinition.getPropertyValues().add("interceptorNames", new ManagedList<String>());
			// copy autowire settings from original bean definition.
			proxyDefinition.setAutowireCandidate(targetDefinition.isAutowireCandidate());
			proxyDefinition.setPrimary(targetDefinition.isPrimary());
			if (targetDefinition instanceof AbstractBeanDefinition) {
				proxyDefinition.copyQualifiersFrom((AbstractBeanDefinition) targetDefinition);
			}
			// wrap it in a BeanDefinitionHolder with bean name
			result = new BeanDefinitionHolder(proxyDefinition, existingBeanName);
		}

		addInterceptorNameToList(interceptorName, result.getBeanDefinition());
		return result;
	}

	@SuppressWarnings("unchecked")
	private void addInterceptorNameToList(String interceptorName, BeanDefinition beanDefinition) {
		List<String> list = (List<String>) beanDefinition.getPropertyValues().get("interceptorNames");
		Assert.state(list != null, "Missing 'interceptorNames' property");
		list.add(interceptorName);
	}

	private boolean isProxyFactoryBeanDefinition(BeanDefinition existingDefinition) {
		return ProxyFactoryBean.class.getName().equals(existingDefinition.getBeanClassName());
	}

	protected String getInterceptorNameSuffix(BeanDefinition interceptorDefinition) {
		String beanClassName = interceptorDefinition.getBeanClassName();
		return (StringUtils.hasLength(beanClassName) ?
				StringUtils.uncapitalize(ClassUtils.getShortName(beanClassName)) : "");
	}

	
Subclasses should implement this method to return the BeanDefinition for the interceptor they wish to apply to the bean being decorated. /**
	 * Subclasses should implement this method to return the {@code BeanDefinition}
	 * for the interceptor they wish to apply to the bean being decorated.
	 */
	protected abstract BeanDefinition createInterceptorDefinition(Node node);

}