一个线程安全的单例模式示例

package com.tecsun.das.collect.modules.util.config;

import com.alibaba.fastjson.JSON;
import net.sf.json.JSONObject;
import org.apache.commons.lang3.StringUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
* Created by Zetting on 2016/9/22.
* Description:读取元配置信息
*/
public class MetaConfg {

private volatile static MetaConfg instance;
private volatile static Map<String,MetadataBean> configs =new HashMap<String, MetadataBean>();

private static Logger logger = LoggerFactory.getLogger(MetaConfg.class);

/**
 * 单例
 * @return
 */
private static MetaConfg getInstance(){
    if(instance == null){
        synchronized (MetaConfg.class){
            if(instance == null){
                instance = new MetaConfg();
            }
        }
    }
    return instance;
}

private MetaConfg(){

}

}