org.springframework.aop.target.EmptyTargetSource Maven / Gradle / Ivy
/*
* 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 java.io.Serializable;
import org.springframework.aop.TargetSource;
import org.springframework.util.ObjectUtils;
/**
* Canonical TargetSource when there is no target
* (or just the target class known), and behavior is supplied
* by interfaces and advisors only.
*
* @author Rod Johnson
* @author Juergen Hoeller
*/
public class EmptyTargetSource implements TargetSource, Serializable {
/** use serialVersionUID from Spring 1.2 for interoperability */
private static final long serialVersionUID = 3680494563553489691L;
//---------------------------------------------------------------------
// Static factory methods
//---------------------------------------------------------------------
/**
* The canonical (Singleton) instance of this {@link EmptyTargetSource}.
*/
public static final EmptyTargetSource INSTANCE = new EmptyTargetSource(null);
/**
* Return an EmptyTargetSource for the given target Class.
* @param targetClass the target Class (may be null)
* @see #getTargetClass()
*/
public static EmptyTargetSource forClass(Class targetClass) {
return (targetClass == null ? INSTANCE : new EmptyTargetSource(targetClass));
}
//---------------------------------------------------------------------
// Instance implementation
//---------------------------------------------------------------------
private final Class targetClass;
/**
* Create a new instance of the {@link EmptyTargetSource} class.
* This constructor is private to enforce the
* Singleton pattern / factory method pattern.
* @param targetClass the target class to expose (may be null)
*/
private EmptyTargetSource(Class targetClass) {
this.targetClass = targetClass;
}
/**
* Always returns the specified target Class, or null if none.
*/
public Class getTargetClass() {
return this.targetClass;
}
/**
* Always returns true.
*/
public boolean isStatic() {
return true;
}
/**
* Always returns null.
*/
public Object getTarget() {
return null;
}
/**
* Nothing to release.
*/
public void releaseTarget(Object target) {
}
/**
* Returns the canonical instance on deserialization in case
* of no target class, thus protecting the Singleton pattern.
*/
private Object readResolve() {
return (this.targetClass == null ? INSTANCE : this);
}
public boolean equals(Object other) {
return (this == other || (other instanceof EmptyTargetSource &&
ObjectUtils.nullSafeEquals(this.targetClass, ((EmptyTargetSource) other).targetClass)));
}
public int hashCode() {
return EmptyTargetSource.class.hashCode() * 13 + ObjectUtils.nullSafeHashCode(this.targetClass);
}
public String toString() {
return "EmptyTargetSource: " +
(this.targetClass != null ? "target class [" + this.targetClass + "]" : "no target class");
}
}