You can create a user-defined method (UDM) containing one or more parameters and return type that is a JSON type.
You cannot create methods for the JSON type. The only methods a JSON type can use are those that are automatically created by Vantage. Therefore, you cannot specify a JSON type name in the FOR clause of a CREATE/REPLACE METHOD statement.
JSON FNC functions and Java classes and methods are provided to enable a UDF, UDM, or external stored procedure to access and set the value of a JSON parameter, or to get information about the JSON type parameter.