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/*
 * Copyright 2002-2007 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
 *
 *      http://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.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.aop.TargetSource;

/**
 * {@link org.springframework.aop.TargetSource} implementation that will
 * lazily create a user-managed object.
 *
 * 

Creation of the lazy target object is controlled by the user by implementing * the {@link #createObject()} method. This TargetSource will invoke * this method the first time the proxy is accessed. * *

Useful when you need to pass a reference to some dependency to an object * but you don't actually want the dependency to be created until it is first used. * A typical scenario for this is a connection to a remote resource. * * @author Rob Harrop * @author Juergen Hoeller * @since 1.2.4 * @see #isInitialized() * @see #createObject() */ public abstract class AbstractLazyCreationTargetSource implements TargetSource { /** Logger available to subclasses */ protected final Log logger = LogFactory.getLog(getClass()); /** The lazily initialized target object */ private Object lazyTarget; /** * Return whether the lazy target object of this TargetSource * has already been fetched. */ public synchronized boolean isInitialized() { return (this.lazyTarget != null); } /** * This default implementation returns null if the * target is null (it is hasn't yet been initialized), * or the target class if the target has already been initialized. *

Subclasses may wish to override this method in order to provide * a meaningful value when the target is still null. * @see #isInitialized() */ public synchronized Class getTargetClass() { return (this.lazyTarget != null ? this.lazyTarget.getClass() : null); } public boolean isStatic() { return false; } /** * Returns the lazy-initialized target object, * creating it on-the-fly if it doesn't exist already. * @see #createObject() */ public synchronized Object getTarget() throws Exception { if (this.lazyTarget == null) { logger.debug("Initializing lazy target object"); this.lazyTarget = createObject(); } return this.lazyTarget; } public void releaseTarget(Object target) throws Exception { // nothing to do } /** * Subclasses should implement this method to return the lazy initialized object. * Called the first time the proxy is invoked. * @return the created object * @throws Exception if creation failed */ protected abstract Object createObject() throws Exception; }





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