/*
 * 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.
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package org.springframework.aop;

import org.springframework.lang.Nullable;

A TargetSource is used to obtain the current "target" of an AOP invocation, which will be invoked via reflection if no around advice chooses to end the interceptor chain itself. 
If a TargetSource is "static", it will always return the same target, allowing optimizations in the AOP framework. Dynamic target sources can support pooling, hot swapping, etc. 
Application developers don't usually need to work with TargetSources directly: this is an AOP framework interface. 
Author:
Rod Johnson, Juergen Hoeller/**
 * A {@code TargetSource} is used to obtain the current "target" of
 * an AOP invocation, which will be invoked via reflection if no around
 * advice chooses to end the interceptor chain itself.
 *
 * <p>If a {@code TargetSource} is "static", it will always return
 * the same target, allowing optimizations in the AOP framework. Dynamic
 * target sources can support pooling, hot swapping, etc.
 *
 * <p>Application developers don't usually need to work with
 * {@code TargetSources} directly: this is an AOP framework interface.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 */
public interface TargetSource extends TargetClassAware {

	
Return the type of targets returned by this TargetSource. 
Can return null, although certain usages of a TargetSource might just work with a predetermined target class. 
Returns:
the type of targets returned by this TargetSource/**
	 * Return the type of targets returned by this {@link TargetSource}.
	 * <p>Can return {@code null}, although certain usages of a {@code TargetSource}
	 * might just work with a predetermined target class.
	 * @return the type of targets returned by this {@link TargetSource}
	 */
	@Override
	@Nullable
	Class<?> getTargetClass();

	
Will all calls to getTarget() return the same object? 
In that case, there will be no need to invoke releaseTarget(Object), and the AOP framework can cache the return value of getTarget(). 
See Also:
getTarget
Returns:
true if the target is immutable/**
	 * Will all calls to {@link #getTarget()} return the same object?
	 * <p>In that case, there will be no need to invoke {@link #releaseTarget(Object)},
	 * and the AOP framework can cache the return value of {@link #getTarget()}.
	 * @return {@code true} if the target is immutable
	 * @see #getTarget
	 */
	boolean isStatic();

	
Return a target instance. Invoked immediately before the
AOP framework calls the "target" of an AOP method invocation.
Throws:
Exception – if the target object can't be resolved
Returns:
the target object which contains the joinpoint, or null if there is no actual target instance/**
	 * Return a target instance. Invoked immediately before the
	 * AOP framework calls the "target" of an AOP method invocation.
	 * @return the target object which contains the joinpoint,
	 * or {@code null} if there is no actual target instance
	 * @throws Exception if the target object can't be resolved
	 */
	@Nullable
	Object getTarget() throws Exception;

	
Release the given target object obtained from the getTarget() method, if any. 
Params:
target – object obtained from a call to getTarget()
Throws:
Exception – if the object can't be released/**
	 * Release the given target object obtained from the
	 * {@link #getTarget()} method, if any.
	 * @param target object obtained from a call to {@link #getTarget()}
	 * @throws Exception if the object can't be released
	 */
	void releaseTarget(Object target) throws Exception;

}