org.springframework.cache.support.AbstractValueAdaptingCache Maven / Gradle / Ivy
/*
* Copyright 2002-2015 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.cache.support;
import org.springframework.cache.Cache;
/**
* Common base class for {@link Cache} implementations that need to adapt
* {@code null} values (and potentially other such special values) before
* passing them on to the underlying store.
*
* Transparently replaces given {@code null} user values with an internal
* {@link NullValue#INSTANCE}, if configured to support {@code null} values
* (as indicated by {@link #isAllowNullValues()}.
*
* @author Juergen Hoeller
* @since 4.2.2
*/
public abstract class AbstractValueAdaptingCache implements Cache {
private final boolean allowNullValues;
/**
* Create an {@code AbstractValueAdaptingCache} with the given setting.
* @param allowNullValues whether to allow for {@code null} values
*/
protected AbstractValueAdaptingCache(boolean allowNullValues) {
this.allowNullValues = allowNullValues;
}
/**
* Return whether {@code null} values are allowed in this cache.
*/
public final boolean isAllowNullValues() {
return this.allowNullValues;
}
@Override
public ValueWrapper get(Object key) {
Object value = lookup(key);
return toValueWrapper(value);
}
@Override
@SuppressWarnings("unchecked")
public T get(Object key, Class type) {
Object value = fromStoreValue(lookup(key));
if (value != null && type != null && !type.isInstance(value)) {
throw new IllegalStateException("Cached value is not of required type [" + type.getName() + "]: " + value);
}
return (T) value;
}
/**
* Perform an actual lookup in the underlying store.
* @param key the key whose associated value is to be returned
* @return the raw store value for the key
*/
protected abstract Object lookup(Object key);
/**
* Convert the given value from the internal store to a user value
* returned from the get method (adapting {@code null}).
* @param storeValue the store value
* @return the value to return to the user
*/
protected Object fromStoreValue(Object storeValue) {
if (this.allowNullValues && storeValue == NullValue.INSTANCE) {
return null;
}
return storeValue;
}
/**
* Convert the given user value, as passed into the put method,
* to a value in the internal store (adapting {@code null}).
* @param userValue the given user value
* @return the value to store
*/
protected Object toStoreValue(Object userValue) {
if (this.allowNullValues && userValue == null) {
return NullValue.INSTANCE;
}
return userValue;
}
/**
* Wrap the given store value with a {@link SimpleValueWrapper}, also going
* through {@link #fromStoreValue} conversion. Useful for {@link #get(Object)}
* and {@link #putIfAbsent(Object, Object)} implementations.
* @param storeValue the original value
* @return the wrapped value
*/
protected Cache.ValueWrapper toValueWrapper(Object storeValue) {
return (storeValue != null ? new SimpleValueWrapper(fromStoreValue(storeValue)) : null);
}
}