jetbrick.ioc.objects.SingletonObject Maven / Gradle / Ivy

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/**
 * Copyright 2013-2014 Guoqiang Chen, Shanghai, China. All rights reserved.
 *
 * Email: [email protected]
 * URL: http://subchen.github.io/
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package jetbrick.ioc.objects;

import jetbrick.ioc.Ioc;

// 单例模式
public abstract class SingletonObject implements IocObject {
    protected final Ioc ioc;
    private boolean initializing;
    private Object object;

    public SingletonObject(Ioc ioc) {
        this.ioc = ioc;
        this.initializing = false;
    }

    @Override
    public Object getObject() {
        if (object == null) {
            synchronized (this) {
                if (object == null) {
                    if (initializing) {
                        throw new IllegalStateException("Cycle dependencies on singleton bean detected: " + toString());
                    }
                    try {
                        initializing = true;
                        object = doGetObject();
                        initializing = false;
                    } catch (RuntimeException e) {
                        throw e;
                    } catch (Exception e) {
                        throw new RuntimeException(e);
                    }
                }
            }
        }
        return object;
    }

    protected abstract Object doGetObject() throws Exception;
}