Question

I have been getting some strange errors with Mongodb, and in Mongodb, you are supposed to mainatin the Mongo singleton. I just wanted to make sure that this is infact valid.

public class DBManager {
    public static Mongo mongoSingleton = null;

    public static synchronized void getMongo(){
         if(mongoSingleton == null){
              mongoSingleton = new Mongo();
         }
         return mongoSingleton;
    }
}

Thanks!

Answer 1

You have to set your public member mongoSingleton as private and to hide the default constructor

so

private static Mongo mongoSingleton = null;

private Mongo() {

}

the class Mongo implementation

public class Mongo {
    private static volatile Mongo instance;
    private Mongo() {
        ...
    }

    public static Mongo getInstance() {
        if (instance == null) {
            synchronized (Mongo.class) {
                if (instance == null) { // yes double check
                    instance = new Mongo();
                }
            }
        }

        return instance;
    }
}

usage

Mongo.getInstance();