001/*
002 * Copyright 2002-2017 the original author or authors.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *      https://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package org.springframework.cache.support;
018
019import java.io.Serializable;
020
021import org.springframework.lang.Nullable;
022
023/**
024 * Simple serializable class that serves as a {@code null} replacement
025 * for cache stores which otherwise do not support {@code null} values.
026 *
027 * @author Juergen Hoeller
028 * @since 4.2.2
029 * @see AbstractValueAdaptingCache
030 */
031public final class NullValue implements Serializable {
032
033        /**
034         * The canonical representation of a {@code null} replacement, as used by the
035         * default implementation of {@link AbstractValueAdaptingCache#toStoreValue}/
036         * {@link AbstractValueAdaptingCache#fromStoreValue}.
037         * @since 4.3.10
038         */
039        public static final Object INSTANCE = new NullValue();
040
041        private static final long serialVersionUID = 1L;
042
043
044        private NullValue() {
045        }
046
047        private Object readResolve() {
048                return INSTANCE;
049        }
050
051
052        @Override
053        public boolean equals(@Nullable Object obj) {
054                return (this == obj || obj == null);
055        }
056
057        @Override
058        public int hashCode() {
059                return NullValue.class.hashCode();
060        }
061
062        @Override
063        public String toString() {
064                return "null";
065        }
066
067}