org.springframework.aop.target.AbstractLazyCreationTargetSource Maven / Gradle / Ivy
/*
* 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.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.aop.TargetSource;
import org.springframework.lang.Nullable;
/**
* {@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 {@code 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 {@code null} if the
* target is {@code 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 {@code null}.
* @see #isInitialized()
*/
@Override
@Nullable
public synchronized Class getTargetClass() {
return (this.lazyTarget != null ? this.lazyTarget.getClass() : null);
}
@Override
public boolean isStatic() {
return false;
}
/**
* Returns the lazy-initialized target object,
* creating it on-the-fly if it doesn't exist already.
* @see #createObject()
*/
@Override
public synchronized Object getTarget() throws Exception {
if (this.lazyTarget == null) {
logger.debug("Initializing lazy target object");
this.lazyTarget = createObject();
}
return this.lazyTarget;
}
@Override
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;
}