001/* -*- mode: Java; c-basic-offset: 2; indent-tabs-mode: nil; coding: utf-8-unix -*-
002 *
003 * Copyright © 2017–2019 microBean.
004 *
005 * Licensed under the Apache License, Version 2.0 (the "License");
006 * you may not use this file except in compliance with the License.
007 * You may obtain a copy of the License at
008 *
009 *     http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
014 * implied.  See the License for the specific language governing
015 * permissions and limitations under the License.
016 */
017package org.microbean.configuration.spi;
018
019import java.util.Map;
020
021import java.util.concurrent.ConcurrentHashMap;
022
023import java.util.function.Function;
024
025import org.microbean.configuration.spi.AbstractResourceLoadingConfiguration.Resource;
026
027public class CachingResourceLoader<T> implements Function<Map<? extends String, ? extends String>, Resource<? extends T>> {
028
029  private final Function<? super Map<? extends String, ? extends String>, ? extends Resource<? extends T>> delegate;
030
031  private final Map<Map<? extends String, ? extends String>, Resource<? extends T>> cache;
032  
033  public CachingResourceLoader(final Function<? super Map<? extends String, ? extends String>, ? extends Resource<? extends T>> delegate) {
034    super();
035    this.delegate = delegate;
036    this.cache = delegate == null ? null : new ConcurrentHashMap<>();
037  }
038
039  public Resource<? extends T> apply(final Map<? extends String, ? extends String> requestedConfigurationCoordinates) {
040    return this.cache == null ? null : this.cache.computeIfAbsent(requestedConfigurationCoordinates, k -> this.delegate.apply(k));
041  }
042
043}