cn.taketoday.aop.target.LazyInitTargetSource Maven / Gradle / Ivy
/*
* Original Author -> Harry Yang ([email protected]) https://taketoday.cn
* Copyright © TODAY & 2017 - 2021 All Rights Reserved.
*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see [http://www.gnu.org/licenses/]
*/
package cn.taketoday.aop.target;
import cn.taketoday.aop.TargetSource;
import cn.taketoday.beans.BeansException;
import cn.taketoday.beans.factory.BeanFactory;
import cn.taketoday.lang.Nullable;
/**
* {@link TargetSource} that lazily accesses a
* singleton bean from a {@link 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
* {@link cn.taketoday.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.
*
For example:
*
*
* <bean id="serviceTarget" class="example.MyService" lazy-init="true">
* ...
* </bean>
*
* <bean id="service" class="cn.taketoday.aop.framework.ProxyFactoryBean">
* <property name="targetSource">
* <bean class="cn.taketoday.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 {@link #postProcessTargetObject(Object)} to
* perform some additional processing with the target object when it is first loaded.
*
* @author Juergen Hoeller
* @author Rob Harrop
* @see BeanFactory#getBean
* @see #postProcessTargetObject
* @since 4.0
*/
@SuppressWarnings("serial")
public class LazyInitTargetSource extends AbstractBeanFactoryTargetSource {
@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.
*
* @param targetObject the target object that has just been instantiated (and configured)
*/
protected void postProcessTargetObject(Object targetObject) { }
}