--- возвращает список txt \ html \ xml
---function MESSAGE_TYPES_LIST return XMLTYPE;

--- возвращает список employees
---function EMPLOYEE_LIST return XMLTYPE;
---  employee  требуется id 
---function EMPLOYEE_GET return XMLTYPE;
---  employee  требуется id 
---function EMPLOYEE_SET return XMLTYPE;
---  employee  создается новый
---function EMPLOYEE_ADD return XMLTYPE;
---  employee  требуется id 
---function EMPLOYEE_DELETE return XMLTYPE;

connection = ds.getConnection();
stmt = (OracleCallableStatement) connection.prepareCall("{ ? = call EMPLOYEE_PACKAGE.EMPLOYEE_LIST() }");
stmt.registerOutParameter(1, OracleTypes.OPAQUE,"SYS.XMLTYPE");
OracleResultSet rs = (OracleResultSet) stmt.executeQuery();

или нужно делать 
???
oracle.sql.OPAQUE  result = (OPAQUE) stmt.getObject(1);

или как то так ? 
stmt.execute();
 XMLType employeexml = XMLType.createXML(stmt.getOPAQUE(1)); 
   
Document employeedoc = (Document) employeexml.getDOM(); 

        connection = ds.getConnection();
        stmt = (OracleCallableStatement) connection.prepareCall("{ ? = call EMPLOYEE_PACKAGE.EMPLOYEE_LIST() }");
        stmt.registerOutParameter(1, OracleTypes.OPAQUE,"SYS.XMLTYPE");
        stmt.execute();

        OPAQUE opaque = stmt.getOPAQUE(1);

OraclePreparedStatement stmt1 = (OraclePreparedStatement) connection.prepareStatement("select EMPLOYEE_PACKAGE.EMPLOYEE_LIST() from dual ");

select EMPLOYEE_PACKAGE.EMPLOYEE_LIST_TYPES() from DUAL;

{<EMPLOYEE_TYPE=admin>,<EMPLOYEE_TYPE=user>,<EMPLOYEE_TYPE=Anonymous>,}

       String sql = "select TYPES_CODE from EMPLOYEE_TABLES.T$EMPLOYEE#TYPES";
       Query q = getEntityManager().createNativeQuery(sql);
       List result = q.getResultList();