/*
 * 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.support;

import java.io.IOException;
import java.io.ObjectInputStream;

import org.aopalliance.aop.Advice;

import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
import org.springframework.beans.factory.config.ConfigurableBeanFactory;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;

Abstract BeanFactory-based PointcutAdvisor that allows for any Advice
to be configured as reference to an Advice bean in a BeanFactory.
Specifying the name of an advice bean instead of the advice object itself
(if running within a BeanFactory) increases loose coupling at initialization time,
in order to not initialize the advice object until the pointcut actually matches.
Author:
Juergen Hoeller
See Also:
setAdviceBeanName
DefaultBeanFactoryPointcutAdvisor
Since:
2.0.2/**
 * Abstract BeanFactory-based PointcutAdvisor that allows for any Advice
 * to be configured as reference to an Advice bean in a BeanFactory.
 *
 * <p>Specifying the name of an advice bean instead of the advice object itself
 * (if running within a BeanFactory) increases loose coupling at initialization time,
 * in order to not initialize the advice object until the pointcut actually matches.
 *
 * @author Juergen Hoeller
 * @since 2.0.2
 * @see #setAdviceBeanName
 * @see DefaultBeanFactoryPointcutAdvisor
 */
@SuppressWarnings("serial")
public abstract class AbstractBeanFactoryPointcutAdvisor extends AbstractPointcutAdvisor implements BeanFactoryAware {

	@Nullable
	private String adviceBeanName;

	@Nullable
	private BeanFactory beanFactory;

	@Nullable
	private transient volatile Advice advice;

	private transient volatile Object adviceMonitor = new Object();


	
Specify the name of the advice bean that this advisor should refer to.
An instance of the specified bean will be obtained on first access
of this advisor's advice. This advisor will only ever obtain at most one
single instance of the advice bean, caching the instance for the lifetime
of the advisor.
See Also:
getAdvice()/**
	 * Specify the name of the advice bean that this advisor should refer to.
	 * <p>An instance of the specified bean will be obtained on first access
	 * of this advisor's advice. This advisor will only ever obtain at most one
	 * single instance of the advice bean, caching the instance for the lifetime
	 * of the advisor.
	 * @see #getAdvice()
	 */
	public void setAdviceBeanName(@Nullable String adviceBeanName) {
		this.adviceBeanName = adviceBeanName;
	}

	
Return the name of the advice bean that this advisor refers to, if any.
/**
	 * Return the name of the advice bean that this advisor refers to, if any.
	 */
	@Nullable
	public String getAdviceBeanName() {
		return this.adviceBeanName;
	}

	@Override
	public void setBeanFactory(BeanFactory beanFactory) {
		this.beanFactory = beanFactory;
		resetAdviceMonitor();
	}

	private void resetAdviceMonitor() {
		if (this.beanFactory instanceof ConfigurableBeanFactory) {
			this.adviceMonitor = ((ConfigurableBeanFactory) this.beanFactory).getSingletonMutex();
		}
		else {
			this.adviceMonitor = new Object();
		}
	}

	
Specify a particular instance of the target advice directly, avoiding lazy resolution in getAdvice(). 
Since:
3.1/**
	 * Specify a particular instance of the target advice directly,
	 * avoiding lazy resolution in {@link #getAdvice()}.
	 * @since 3.1
	 */
	public void setAdvice(Advice advice) {
		synchronized (this.adviceMonitor) {
			this.advice = advice;
		}
	}

	@Override
	public Advice getAdvice() {
		Advice advice = this.advice;
		if (advice != null) {
			return advice;
		}

		Assert.state(this.adviceBeanName != null, "'adviceBeanName' must be specified");
		Assert.state(this.beanFactory != null, "BeanFactory must be set to resolve 'adviceBeanName'");

		if (this.beanFactory.isSingleton(this.adviceBeanName)) {
			// Rely on singleton semantics provided by the factory.
			advice = this.beanFactory.getBean(this.adviceBeanName, Advice.class);
			this.advice = advice;
			return advice;
		}
		else {
			// No singleton guarantees from the factory -> let's lock locally but
			// reuse the factory's singleton lock, just in case a lazy dependency
			// of our advice bean happens to trigger the singleton lock implicitly...
			synchronized (this.adviceMonitor) {
				advice = this.advice;
				if (advice == null) {
					advice = this.beanFactory.getBean(this.adviceBeanName, Advice.class);
					this.advice = advice;
				}
				return advice;
			}
		}
	}

	@Override
	public String toString() {
		StringBuilder sb = new StringBuilder(getClass().getName());
		sb.append(": advice ");
		if (this.adviceBeanName != null) {
			sb.append("bean '").append(this.adviceBeanName).append("'");
		}
		else {
			sb.append(this.advice);
		}
		return sb.toString();
	}


	//---------------------------------------------------------------------
	// Serialization support
	//---------------------------------------------------------------------

	private void readObject(ObjectInputStream ois) throws IOException, ClassNotFoundException {
		// Rely on default serialization, just initialize state after deserialization.
		ois.defaultReadObject();

		// Initialize transient fields.
		resetAdviceMonitor();
	}

}