001/*
002 * Copyright 2002-2012 the original author or authors.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *      https://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package org.springframework.aop.target;
018
019import org.springframework.beans.BeansException;
020import org.springframework.lang.Nullable;
021
022/**
023 * {@link org.springframework.aop.TargetSource} that lazily accesses a
024 * singleton bean from a {@link org.springframework.beans.factory.BeanFactory}.
025 *
026 * <p>Useful when a proxy reference is needed on initialization but
027 * the actual target object should not be initialized until first use.
028 * When the target bean is defined in an
029 * {@link org.springframework.context.ApplicationContext} (or a
030 * {@code BeanFactory} that is eagerly pre-instantiating singleton beans)
031 * it must be marked as "lazy-init" too, else it will be instantiated by said
032 * {@code ApplicationContext} (or {@code BeanFactory}) on startup.
033 * <p>For example:
034 *
035 * <pre class="code">
036 * &lt;bean id="serviceTarget" class="example.MyService" lazy-init="true"&gt;
037 *   ...
038 * &lt;/bean&gt;
039 *
040 * &lt;bean id="service" class="org.springframework.aop.framework.ProxyFactoryBean"&gt;
041 *   &lt;property name="targetSource"&gt;
042 *     &lt;bean class="org.springframework.aop.target.LazyInitTargetSource"&gt;
043 *       &lt;property name="targetBeanName"&gt;&lt;idref local="serviceTarget"/&gt;&lt;/property&gt;
044 *     &lt;/bean&gt;
045 *   &lt;/property&gt;
046 * &lt;/bean&gt;</pre>
047 *
048 * The "serviceTarget" bean will not get initialized until a method on the
049 * "service" proxy gets invoked.
050 *
051 * <p>Subclasses can extend this class and override the {@link #postProcessTargetObject(Object)} to
052 * perform some additional processing with the target object when it is first loaded.
053 *
054 * @author Juergen Hoeller
055 * @author Rob Harrop
056 * @since 1.1.4
057 * @see org.springframework.beans.factory.BeanFactory#getBean
058 * @see #postProcessTargetObject
059 */
060@SuppressWarnings("serial")
061public class LazyInitTargetSource extends AbstractBeanFactoryBasedTargetSource {
062
063        @Nullable
064        private Object target;
065
066
067        @Override
068        @Nullable
069        public synchronized Object getTarget() throws BeansException {
070                if (this.target == null) {
071                        this.target = getBeanFactory().getBean(getTargetBeanName());
072                        postProcessTargetObject(this.target);
073                }
074                return this.target;
075        }
076
077        /**
078         * Subclasses may override this method to perform additional processing on
079         * the target object when it is first loaded.
080         * @param targetObject the target object that has just been instantiated (and configured)
081         */
082        protected void postProcessTargetObject(Object targetObject) {
083        }
084
085}