/*
* Copyright 2002-2005 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.util;
import java.io.Serializable;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import java.util.WeakHashMap;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
/**
* A simple decorator for a Map, encapsulating the workflow for caching
* expensive values in a target Map. Supports caching weak or strong keys.
*
* <p>This class is also an abstract template. Caching Map implementations
* should subclass and override the <code>create(key)</code> method which
* encapsulates expensive creation of a new object.
*
* @author Keith Donald
* @since 1.2.2
*/
public abstract class CachingMapDecorator implements Map, Serializable {
private static Object NULL_VALUE = new Object();
private static final Log logger = LogFactory.getLog(CachingMapDecorator.class);
private final Map targetMap;
/**
* Create a CachingMapDecorator with strong keys,
* using an underlying synchronized Map.
*/
public CachingMapDecorator() {
this(false);
}
/**
* Create a CachingMapDecorator,
* using an underlying synchronized Map.
* @param weakKeys whether to use weak references for keys
*/
public CachingMapDecorator(boolean weakKeys) {
Map internalMap = weakKeys ? (Map) new WeakHashMap() : new HashMap();
this.targetMap = Collections.synchronizedMap(internalMap);
}
/**
* Create a CachingMapDecorator with initial size,
* using an underlying synchronized Map.
* @param weakKeys whether to use weak references for keys
* @param size the initial cache size
*/
public CachingMapDecorator(boolean weakKeys, int size) {
Map internalMap = weakKeys ? (Map) new WeakHashMap(size) : new HashMap(size);
this.targetMap = Collections.synchronizedMap(internalMap);
}
/**
* Create a CachingMapDecorator for the given Map.
* <p>The passed-in Map won't get synchronized explicitly,
* so make sure to pass in a properly synchronized Map, if desired.
* @param targetMap the Map to decorate
*/
public CachingMapDecorator(Map targetMap) {
Assert.notNull(targetMap, "Target Map is required");
this.targetMap = targetMap;
}
public int size() {
return this.targetMap.size();
}
public boolean isEmpty() {
return this.targetMap.isEmpty();
}
public boolean containsKey(Object key) {
return this.targetMap.containsKey(key);
}
public boolean containsValue(Object value) {
return this.targetMap.containsValue(value);
}
public Object put(Object key, Object value) {
return this.targetMap.put(key, value);
}
public Object remove(Object key) {
return this.targetMap.remove(key);
}
public void putAll(Map t) {
this.targetMap.putAll(t);
}
public void clear() {
this.targetMap.clear();
}
public Set keySet() {
return this.targetMap.keySet();
}
public Collection values() {
return this.targetMap.values();
}
public Set entrySet() {
return this.targetMap.entrySet();
}
/**
* Get value for key.
* Creates and caches value if it doesn't already exist in the cache.
* <p>This implementation is <i>not</i> synchronized: This is highly
* concurrent but does not guarantee unique instances in the cache,
* as multiple values for the same key could get created in parallel.
* Consider overriding this method to synchronize it, if desired.
* @see #create(Object)
*/
public Object get(Object key) {
Object value = this.targetMap.get(key);
if (value == null) {
if (logger.isDebugEnabled()) {
logger.debug("Creating new expensive value for key '" + key + "'");
}
value = create(key);
if (value == null) {
value = NULL_VALUE;
}
if (logger.isDebugEnabled()) {
logger.debug("Caching expensive value: " + value);
}
put(key, value);
}
else {
if (logger.isDebugEnabled()) {
logger.debug("For key '" + key + "', returning cached value: " + value);
}
}
return (value == NULL_VALUE) ? null : value;
}
/**
* Create a value to cache for the given key.
* Called by <code>get</code> if there is no value cached already.
* @param key the cache key
* @see #get(Object)
*/
protected abstract Object create(Object key);
public String toString() {
return "CachingMapDecorator [" + getClass().getName() + "]:" + this.targetMap;
}
}