001    // Copyright 2011 The Apache Software Foundation
002    //
003    // Licensed under the Apache License, Version 2.0 (the "License");
004    // you may not use this file except in compliance with the License.
005    // You may obtain a copy of the License at
006    //
007    // http://www.apache.org/licenses/LICENSE-2.0
008    //
009    // Unless required by applicable law or agreed to in writing, software
010    // distributed under the License is distributed on an "AS IS" BASIS,
011    // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012    // See the License for the specific language governing permissions and
013    // limitations under the License.
014    
015    package org.apache.tapestry5.internal.plastic;
016    
017    import java.util.HashMap;
018    import java.util.Map;
019    
020    /**
021     * Quick and dirty key/value cache that is subclassed to provide the logic that generates the value for
022     * a missing key.
023     * 
024     * @param <S>
025     * @param <T>
026     */
027    public abstract class Cache<S, T>
028    {
029        private Map<S, T> innerCache = new HashMap<S, T>();
030    
031        public T get(S input)
032        {
033            T result = innerCache.get(input);
034    
035            if (result == null)
036            {
037                result = convert(input);
038                innerCache.put(input, result);
039            }
040    
041            return result;
042        }
043    
044        protected abstract T convert(S input);
045    }