/*
 * Copyright 2002-2018 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.target;

import org.springframework.aop.support.DefaultIntroductionAdvisor;
import org.springframework.aop.support.DelegatingIntroductionInterceptor;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanInitializationException;
import org.springframework.beans.factory.DisposableBean;
import org.springframework.lang.Nullable;

Abstract base class for pooling TargetSource implementations which maintain a pool of target instances, acquiring and releasing a target object from the pool for each method invocation. This abstract base class is independent of concrete pooling technology; see the subclass CommonsPool2TargetSource for a concrete example. 
Subclasses must implement the getTarget and releaseTarget methods based on their chosen object pool. The AbstractPrototypeBasedTargetSource.newPrototypeInstance() method inherited from AbstractPrototypeBasedTargetSource can be used to create objects in order to put them into the pool. 
Subclasses must also implement some of the monitoring methods from the PoolingConfig interface. The getPoolingConfigMixin() method makes these stats available on proxied objects through an IntroductionAdvisor. 
This class implements the DisposableBean interface in order to force subclasses to implement a DisposableBean.destroy() method, closing down their object pool. 
Author:
Rod Johnson, Juergen Hoeller
See Also:
getTarget
releaseTarget
DisposableBean.destroy/**
 * Abstract base class for pooling {@link org.springframework.aop.TargetSource}
 * implementations which maintain a pool of target instances, acquiring and
 * releasing a target object from the pool for each method invocation.
 * This abstract base class is independent of concrete pooling technology;
 * see the subclass {@link CommonsPool2TargetSource} for a concrete example.
 *
 * <p>Subclasses must implement the {@link #getTarget} and
 * {@link #releaseTarget} methods based on their chosen object pool.
 * The {@link #newPrototypeInstance()} method inherited from
 * {@link AbstractPrototypeBasedTargetSource} can be used to create objects
 * in order to put them into the pool.
 *
 * <p>Subclasses must also implement some of the monitoring methods from the
 * {@link PoolingConfig} interface. The {@link #getPoolingConfigMixin()} method
 * makes these stats available on proxied objects through an IntroductionAdvisor.
 *
 * <p>This class implements the {@link org.springframework.beans.factory.DisposableBean}
 * interface in order to force subclasses to implement a {@link #destroy()}
 * method, closing down their object pool.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @see #getTarget
 * @see #releaseTarget
 * @see #destroy
 */
@SuppressWarnings("serial")
public abstract class AbstractPoolingTargetSource extends AbstractPrototypeBasedTargetSource
		implements PoolingConfig, DisposableBean {

	
The maximum size of the pool. /** The maximum size of the pool. */
	private int maxSize = -1;


	
Set the maximum size of the pool.
Default is -1, indicating no size limit.
/**
	 * Set the maximum size of the pool.
	 * Default is -1, indicating no size limit.
	 */
	public void setMaxSize(int maxSize) {
		this.maxSize = maxSize;
	}

	
Return the maximum size of the pool.
/**
	 * Return the maximum size of the pool.
	 */
	@Override
	public int getMaxSize() {
		return this.maxSize;
	}


	@Override
	public final void setBeanFactory(BeanFactory beanFactory) throws BeansException {
		super.setBeanFactory(beanFactory);
		try {
			createPool();
		}
		catch (Throwable ex) {
			throw new BeanInitializationException("Could not create instance pool for TargetSource", ex);
		}
	}


	
Create the pool.
Throws:
Exception – to avoid placing constraints on pooling APIs/**
	 * Create the pool.
	 * @throws Exception to avoid placing constraints on pooling APIs
	 */
	protected abstract void createPool() throws Exception;

	
Acquire an object from the pool.
Throws:
Exception – we may need to deal with checked exceptions from pool
APIs, so we're forgiving with our exception signature
Returns:
an object from the pool/**
	 * Acquire an object from the pool.
	 * @return an object from the pool
	 * @throws Exception we may need to deal with checked exceptions from pool
	 * APIs, so we're forgiving with our exception signature
	 */
	@Override
	@Nullable
	public abstract Object getTarget() throws Exception;

	
Return the given object to the pool.
Params:
target – object that must have been acquired from the pool via a call to getTarget()
Throws:
Exception – to allow pooling APIs to throw exception
See Also:
getTarget/**
	 * Return the given object to the pool.
	 * @param target object that must have been acquired from the pool
	 * via a call to {@code getTarget()}
	 * @throws Exception to allow pooling APIs to throw exception
	 * @see #getTarget
	 */
	@Override
	public abstract void releaseTarget(Object target) throws Exception;


	
Return an IntroductionAdvisor that providing a mixin
exposing statistics about the pool maintained by this object.
/**
	 * Return an IntroductionAdvisor that providing a mixin
	 * exposing statistics about the pool maintained by this object.
	 */
	public DefaultIntroductionAdvisor getPoolingConfigMixin() {
		DelegatingIntroductionInterceptor dii = new DelegatingIntroductionInterceptor(this);
		return new DefaultIntroductionAdvisor(dii, PoolingConfig.class);
	}

}