Java 为mongo创建单例类

我正在尝试为java mongo驱动程序编写singleton。我试过这段代码，但它不正确。帮我纠正我的逻辑

public class MySingleton extends Mongo{
    private static MySingleton instance = null;
    private static Mongo mongo = null;

    protected MySingleton () 
          throws UnknownHostException,UnsupportedOperationException{


    }

    protected MySingleton (String ip, int port) 
               throws UnknownHostException,UnsupportedOperationException{

        mongo = new Mongo(ip,port);
        instance = (MySingleton) mongo;
    }

    public static synchronized MySingleton getInstance(String ip, int port) 
                     throws UnknownHostException{

        if (instance == null){
          instance =  new MySingleton(ip,port);
        }

         return instance;
    }
}

我得到了ClassCast异常，例如=（MySingleton）mongo；，这显然是错误的

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我已经知道MongoClient。Holder.singleton（）。connect（）方法，但它不能解决我的问题。因此，我希望创建自己的singleton类。

既然已经在扩展mongo实例，为什么还要保存另一个mongo实例呢

public class MySingleton extends Mongo{
    private static MySingleton instance = null;

    protected MySingleton () 
          throws UnknownHostException,UnsupportedOperationException{


    }

    protected MySingleton (String ip, int port) 
               throws UnknownHostException,UnsupportedOperationException{
        super(ip, port);
    }

    public static synchronized MySingleton getInstance(String ip, int port) 
                     throws UnknownHostException{

        if (instance == null){
          instance =  new MySingleton(ip,port);
        }

         return instance;
    }
}

如果您需要一个mongo实例，可以使用以下方法

 Mongo m = MySingleton.getInstance(ip,port);

我还建议您阅读以下内容，以便您可以使用其示例7。一个简单的单例

public class Singleton {
   public final static Singleton INSTANCE = new Singleton();
   private Singleton() {
         // Exists only to defeat instantiation.
      }
}   

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我们定义了MongoDB对MySingleton接口的实现

public类实现MySingleton
{
}