    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    }