001/* 002 * Copyright 2002-2020 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 org.springframework.cache.Cache; 020import org.springframework.lang.Nullable; 021 022/** 023 * Common base class for {@link Cache} implementations that need to adapt 024 * {@code null} values (and potentially other such special values) before 025 * passing them on to the underlying store. 026 * 027 * <p>Transparently replaces given {@code null} user values with an internal 028 * {@link NullValue#INSTANCE}, if configured to support {@code null} values 029 * (as indicated by {@link #isAllowNullValues()}. 030 * 031 * @author Juergen Hoeller 032 * @since 4.2.2 033 */ 034public abstract class AbstractValueAdaptingCache implements Cache { 035 036 private final boolean allowNullValues; 037 038 039 /** 040 * Create an {@code AbstractValueAdaptingCache} with the given setting. 041 * @param allowNullValues whether to allow for {@code null} values 042 */ 043 protected AbstractValueAdaptingCache(boolean allowNullValues) { 044 this.allowNullValues = allowNullValues; 045 } 046 047 048 /** 049 * Return whether {@code null} values are allowed in this cache. 050 */ 051 public final boolean isAllowNullValues() { 052 return this.allowNullValues; 053 } 054 055 @Override 056 @Nullable 057 public ValueWrapper get(Object key) { 058 return toValueWrapper(lookup(key)); 059 } 060 061 @Override 062 @SuppressWarnings("unchecked") 063 @Nullable 064 public <T> T get(Object key, @Nullable Class<T> type) { 065 Object value = fromStoreValue(lookup(key)); 066 if (value != null && type != null && !type.isInstance(value)) { 067 throw new IllegalStateException( 068 "Cached value is not of required type [" + type.getName() + "]: " + value); 069 } 070 return (T) value; 071 } 072 073 /** 074 * Perform an actual lookup in the underlying store. 075 * @param key the key whose associated value is to be returned 076 * @return the raw store value for the key, or {@code null} if none 077 */ 078 @Nullable 079 protected abstract Object lookup(Object key); 080 081 082 /** 083 * Convert the given value from the internal store to a user value 084 * returned from the get method (adapting {@code null}). 085 * @param storeValue the store value 086 * @return the value to return to the user 087 */ 088 @Nullable 089 protected Object fromStoreValue(@Nullable Object storeValue) { 090 if (this.allowNullValues && storeValue == NullValue.INSTANCE) { 091 return null; 092 } 093 return storeValue; 094 } 095 096 /** 097 * Convert the given user value, as passed into the put method, 098 * to a value in the internal store (adapting {@code null}). 099 * @param userValue the given user value 100 * @return the value to store 101 */ 102 protected Object toStoreValue(@Nullable Object userValue) { 103 if (userValue == null) { 104 if (this.allowNullValues) { 105 return NullValue.INSTANCE; 106 } 107 throw new IllegalArgumentException( 108 "Cache '" + getName() + "' is configured to not allow null values but null was provided"); 109 } 110 return userValue; 111 } 112 113 /** 114 * Wrap the given store value with a {@link SimpleValueWrapper}, also going 115 * through {@link #fromStoreValue} conversion. Useful for {@link #get(Object)} 116 * and {@link #putIfAbsent(Object, Object)} implementations. 117 * @param storeValue the original value 118 * @return the wrapped value 119 */ 120 @Nullable 121 protected Cache.ValueWrapper toValueWrapper(@Nullable Object storeValue) { 122 return (storeValue != null ? new SimpleValueWrapper(fromStoreValue(storeValue)) : null); 123 } 124 125}