001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing,
013 * software distributed under the License is distributed on an
014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 * KIND, either express or implied.  See the License for the
016 * specific language governing permissions and limitations
017 * under the License.
018 */
019package org.apache.shiro.util;
020
021/**
022 * TODO - Class JavaDoc
023 *
024 * @since 1.0
025 */
026public abstract class AbstractFactory<T> implements Factory<T> {
027
028    private boolean singleton;
029    private T singletonInstance;
030
031    public AbstractFactory() {
032        this.singleton = true;
033    }
034
035    public boolean isSingleton() {
036        return singleton;
037    }
038
039    public void setSingleton(boolean singleton) {
040        this.singleton = singleton;
041    }
042
043    public T getInstance() {
044        T instance;
045        if (isSingleton()) {
046            if (this.singletonInstance == null) {
047                this.singletonInstance = createInstance();
048            }
049            instance = this.singletonInstance;
050        } else {
051            instance = createInstance();
052        }
053        if (instance == null) {
054            String msg = "Factory 'createInstance' implementation returned a null object.";
055            throw new IllegalStateException(msg);
056        }
057        return instance;
058    }
059
060    protected abstract T createInstance();
061}