java - 为mongo创建单例类

Question

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

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;
    }
}

我收到 ClassCast 异常，例如 = (MySingleton) mongo;，这显然是不正确的。

我已经知道 MongoClient。 Holder.singleton(). connect() 方法，但它没有解决我的问题。所以我希望创建自己的单例类。

Answer 1

为什么您已经扩展了另一个 mongo 实例？

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;
    }
}

如果你需要一个mongo实例，你可以使用下面的方式。

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

我还建议阅读以下内容 singleton article这样您就可以使用它的示例 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.
      }
}