org.springframework.aop.target.EmptyTargetSource Maven / Gradle / Ivy
/*
* Copyright 2002-2023 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 java.io.Serializable;
import java.util.Objects;
import org.springframework.aop.TargetSource;
import org.springframework.lang.Nullable;
import org.springframework.util.ObjectUtils;
/**
* Canonical {@code 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 final 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, true);
/**
* Return an EmptyTargetSource for the given target Class.
* @param targetClass the target Class (may be {@code null})
* @see #getTargetClass()
*/
public static EmptyTargetSource forClass(@Nullable Class targetClass) {
return forClass(targetClass, true);
}
/**
* Return an EmptyTargetSource for the given target Class.
* @param targetClass the target Class (may be {@code null})
* @param isStatic whether the TargetSource should be marked as static
* @see #getTargetClass()
*/
public static EmptyTargetSource forClass(@Nullable Class targetClass, boolean isStatic) {
return (targetClass == null && isStatic ? INSTANCE : new EmptyTargetSource(targetClass, isStatic));
}
//---------------------------------------------------------------------
// Instance implementation
//---------------------------------------------------------------------
@Nullable
private final Class targetClass;
private final boolean isStatic;
/**
* Create a new instance of the {@link EmptyTargetSource} class.
* This constructor is {@code private} to enforce the
* Singleton pattern / factory method pattern.
* @param targetClass the target class to expose (may be {@code null})
* @param isStatic whether the TargetSource is marked as static
*/
private EmptyTargetSource(@Nullable Class targetClass, boolean isStatic) {
this.targetClass = targetClass;
this.isStatic = isStatic;
}
/**
* Always returns the specified target Class, or {@code null} if none.
*/
@Override
@Nullable
public Class getTargetClass() {
return this.targetClass;
}
/**
* Always returns {@code true}.
*/
@Override
public boolean isStatic() {
return this.isStatic;
}
/**
* Always returns {@code null}.
*/
@Override
@Nullable
public Object getTarget() {
return null;
}
/**
* Returns the canonical instance on deserialization in case
* of no target class, thus protecting the Singleton pattern.
*/
private Object readResolve() {
return (this.targetClass == null && this.isStatic ? INSTANCE : this);
}
@Override
public boolean equals(@Nullable Object other) {
return (this == other || (other instanceof EmptyTargetSource that &&
ObjectUtils.nullSafeEquals(this.targetClass, that.targetClass) &&
this.isStatic == that.isStatic));
}
@Override
public int hashCode() {
return Objects.hash(getClass(), this.targetClass);
}
@Override
public String toString() {
return "EmptyTargetSource: " +
(this.targetClass != null ? "target class [" + this.targetClass.getName() + "]" : "no target class") +
", " + (this.isStatic ? "static" : "dynamic");
}
}