driver-legacy/src/main/com/mongodb/DBCollection.java
@Nullable
    public DBObject findOne(@Nullable final DBObject query, final DBCollectionFindOptions findOptions) {
        return find(query, findOptions).one();
    }
@Nullable
    public DBObject findOne(@Nullable final DBObject query, final DBCollectionFindOptions findOptions) {
        return find(query, findOptions).one();
    }
@ Nullable public DBObject findOne ( @ Nullable final DBObject query , final DBCollectionFindOptions findOptions ) { return find ( query , findOptions ) . one ( ) ; }
Get a single document from collection.

@param query          the selection criteria using query operators.
@param findOptions    the options for the find operation.
@return A document that satisfies the query specified as the argument to this method.
@mongodb.driver.manual tutorial/query-documents/ Querying
@since 3.4
Get a single document from collection .