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
021import org.apache.shiro.lang.util.Factory;
022
023/**
024 * AbstractFactory.
025 *
026 * @param <T> T
027 * @since 1.0
028 */
029public abstract class AbstractFactory<T> implements Factory<T> {
030
031    private boolean singleton;
032    private T singletonInstance;
033
034    public AbstractFactory() {
035        this.singleton = true;
036    }
037
038    public boolean isSingleton() {
039        return singleton;
040    }
041
042    public void setSingleton(boolean singleton) {
043        this.singleton = singleton;
044    }
045
046    public T getInstance() {
047        T instance;
048        if (isSingleton()) {
049            if (this.singletonInstance == null) {
050                this.singletonInstance = createInstance();
051            }
052            instance = this.singletonInstance;
053        } else {
054            instance = createInstance();
055        }
056        if (instance == null) {
057            String msg = "Factory 'createInstance' implementation returned a null object.";
058            throw new IllegalStateException(msg);
059        }
060        return instance;
061    }
062
063    protected abstract T createInstance();
064}