/*
 * 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
 *
 *      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.beans.BeansException;
import org.springframework.lang.Nullable;

TargetSource that lazily accesses a singleton bean from a BeanFactory. 
Useful when a proxy reference is needed on initialization but the actual target object should not be initialized until first use. When the target bean is defined in an ApplicationContext (or a BeanFactory that is eagerly pre-instantiating singleton beans) it must be marked as "lazy-init" too, else it will be instantiated by said ApplicationContext (or BeanFactory) on startup. 
For example:
<bean id="serviceTarget" class="example.MyService" lazy-init="true">
  ...
</bean>
<bean id="service" class="org.springframework.aop.framework.ProxyFactoryBean">
  <property name="targetSource">
    <bean class="org.springframework.aop.target.LazyInitTargetSource">
      <property name="targetBeanName"><idref local="serviceTarget"/></property>
    </bean>
  </property>
</bean>
The "serviceTarget" bean will not get initialized until a method on the
"service" proxy gets invoked.
Subclasses can extend this class and override the postProcessTargetObject(Object) to perform some additional processing with the target object when it is first loaded. 
Author:
Juergen Hoeller, Rob Harrop
See Also:
BeanFactory.getBean
postProcessTargetObject
Since:
1.1.4/**
 * {@link org.springframework.aop.TargetSource} that lazily accesses a
 * singleton bean from a {@link org.springframework.beans.factory.BeanFactory}.
 *
 * <p>Useful when a proxy reference is needed on initialization but
 * the actual target object should not be initialized until first use.
 * When the target bean is defined in an
 * {@link org.springframework.context.ApplicationContext} (or a
 * {@code BeanFactory} that is eagerly pre-instantiating singleton beans)
 * it must be marked as "lazy-init" too, else it will be instantiated by said
 * {@code ApplicationContext} (or {@code BeanFactory}) on startup.
 * <p>For example:
 *
 * <pre class="code">
 * &lt;bean id="serviceTarget" class="example.MyService" lazy-init="true"&gt;
 *   ...
 * &lt;/bean&gt;
 *
 * &lt;bean id="service" class="org.springframework.aop.framework.ProxyFactoryBean"&gt;
 *   &lt;property name="targetSource"&gt;
 *     &lt;bean class="org.springframework.aop.target.LazyInitTargetSource"&gt;
 *       &lt;property name="targetBeanName"&gt;&lt;idref local="serviceTarget"/&gt;&lt;/property&gt;
 *     &lt;/bean&gt;
 *   &lt;/property&gt;
 * &lt;/bean&gt;</pre>
 *
 * The "serviceTarget" bean will not get initialized until a method on the
 * "service" proxy gets invoked.
 *
 * <p>Subclasses can extend this class and override the {@link #postProcessTargetObject(Object)} to
 * perform some additional processing with the target object when it is first loaded.
 *
 * @author Juergen Hoeller
 * @author Rob Harrop
 * @since 1.1.4
 * @see org.springframework.beans.factory.BeanFactory#getBean
 * @see #postProcessTargetObject
 */
@SuppressWarnings("serial")
public class LazyInitTargetSource extends AbstractBeanFactoryBasedTargetSource {

	@Nullable
	private Object target;


	@Override
	@Nullable
	public synchronized Object getTarget() throws BeansException {
		if (this.target == null) {
			this.target = getBeanFactory().getBean(getTargetBeanName());
			postProcessTargetObject(this.target);
		}
		return this.target;
	}

	
Subclasses may override this method to perform additional processing on
the target object when it is first loaded.
Params:
targetObject – the target object that has just been instantiated (and configured)/**
	 * Subclasses may override this method to perform additional processing on
	 * the target object when it is first loaded.
	 * @param targetObject the target object that has just been instantiated (and configured)
	 */
	protected void postProcessTargetObject(Object targetObject) {
	}

}