@Nullable
    public DBObject findOne(final DBObject query, final DBObject projection) {
        return findOne(query, projection, null, getReadPreference());
    }
@Nullable
    public DBObject findOne(final DBObject query, final DBObject projection) {
        return findOne(query, projection, null, getReadPreference());
    }
@ Nullable public DBObject findOne ( final DBObject query , final DBObject projection ) { return findOne ( query , projection , null , getReadPreference ( ) ) ; }
Get a single document from collection.

@param query      the selection criteria using query operators.
@param projection specifies which fields MongoDB will return from the documents in the result set.
@return A document that satisfies the query specified as the argument to this method.
@mongodb.driver.manual tutorial/query-documents/ Querying
Get a single document from collection .