001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  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 implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.wicket.util.reference;
018
019import java.io.Serializable;
020import java.lang.ref.WeakReference;
021import java.util.function.Supplier;
022
023import org.apache.wicket.core.util.lang.WicketObjects;
024
025/**
026 * A serialization-safe reference to a {@link Class}
027 * 
028 * @author igor
029 * 
030 * @param <T>
031 *            type of class
032 */
033public class ClassReference<T> implements Serializable, Supplier<Class<T>>
034{
035        private static final long serialVersionUID = 1L;
036
037        private transient WeakReference<Class<T>> cache;
038        private final String name;
039
040        /**
041         * Constructor
042         * 
043         * @param clazz
044         *          The referenced class
045         */
046        public ClassReference(Class<T> clazz)
047        {
048                name = clazz.getName();
049                cache(clazz);
050        }
051
052        /**
053         * @return the {@link Class} stored in this reference
054         */
055        @Override
056        public Class<T> get()
057        {
058                Class<T> clazz = cache != null ? cache.get() : null;
059                if (clazz == null)
060                {
061                        clazz = WicketObjects.resolveClass(name);
062                        if (clazz == null)
063                        {
064                                throw new RuntimeException("Could not resolve class: " + name);
065                        }
066                        cache(clazz);
067                }
068                return clazz;
069        }
070
071        private void cache(Class<T> clazz)
072        {
073                cache = new WeakReference<>(clazz);
074        }
075
076        /**
077         * Diamond operator factory
078         * 
079         * @param clazz
080         *          The referenced class
081         * @return class reference
082         */
083        public static <T> ClassReference<T> of(Class<T> clazz)
084        {
085                return new ClassReference<>(clazz);
086        }
087}