Java Stored Procedure: Invalid call: it can not return ResultSet

I am running the following example in my cubrid database.

function:

create function rset() return cursor
as language java
name 'JavaSP2.TResultSet() return java.sql.ResultSet'

Stored procedure:

public static class JavaSP2 {
public static ResultSet TResultSet(){

try{
Class.forName("cubrid.jdbc.driver.CUBRIDDriver");
Connection conn = DriverManager.getConnection("jdbc:default:connection:");
((CUBRIDConnection)con).setCharset("euc_kr");

String sql = "select * from station";
Statement stmt=con.createStatement();
ResultSet rs = stmt.executeQuery(sql);
((CUBRIDResultSet)rs).setReturnable();

return rs;
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
} 

CUBRID says:   

execute error:-911
line 1 is not executed (error)Error description:
Invalid call: it can not return ResultSet. 

I try to solve it doing casting but dont work. When I registering the function cubrid dont allow set  java.sql.ResultSet as return value instead use

CREATE FUNCTION "rset"() RETURN CURSOR
AS LANGUAGE JAVA 
NAME 'JavaSP2.TResultSet() return cubrid.jdbc.driver.CUBRIDResultSet'