Can't get time zone information when using mod_plsql? - oracle

Question

I have written a function to convert a date into a Unix time stamp. The function is written to work no matter what the current DST status is (e.g. EST or EDT). This is the function:
function unix_time_from_date(in_date in date) return number
as
ut number := 0;
tz varchar2(8) := '';
begin
-- Get the local timezone from the passed in date
-- Assuming the date supplied is for the local time zone
select
extract(
timezone_abbr from cast(in_date as timestamp with local time zone)
)
into tz
from dual;
-- Get the Unix timestamp
select
(new_time(in_date, tz, 'GMT') - to_date('01-JAN-1970', 'DD-MM-YYYY')) * (
86400)
into ut
from dual;
return ut;
end unix_time_from_date;
This function works great when I execute it from a client like JDeveloper. From what I gather, this is because the client is supplying time zone information to the first query. However, if I use the function from within a procedure that is called from a mod_plsql page, then I get the error ORA-01857: not a valid time zone. This error is being thrown from the new_time function because tz is set to 'UNK'.
So, I implemented a work-around for this problem like so:
function unix_time_from_date(in_date in date) return number
as
ut number := 0;
tz varchar2(8) := '';
begin
-- Get the local timezone from the passed in date
-- Assuming the date supplied is for the local time zone
select
extract(
timezone_abbr from cast(in_date as timestamp with local time zone)
)
into tz
from dual;
if tz = 'UNK' then
select
extract(
timezone_abbr from cast(sysdate as timestamp with local time zone)
)
into tz
from dual;
end if;
-- Get the Unix timestamp
select
(new_time(in_date, tz, 'GMT') - to_date('01-JAN-1970', 'DD-MM-YYYY')) * (
86400)
into ut
from dual;
return ut;
end unix_time_from_date;
Except, this still fails with tz being set to 'UNK'. Does anyone know what could be happening here? Why can't I get the local time zone abbreviation when the function is called from a Oracle Application Server process?

Answer 1

I guess this does not depends on the date parameter you are passing. It probably depends on the Operating system settings where the database server runs. In JDeveloper it is probably picking up from your Computers (OS) time zone settings. Try doing an ssh on the DB server and run the first two queries in your script (use the actual date in 'DD-MON-YY' format for first query). Both should be returning 'UNK'. The UNK (unknown) is likely because more than one timezone is returned.Examples: In the following examples, suppose that the current time zone is CST (US Central Time).
SELECT NEW_TIME(SYSDATE, 'CST', 'GMT') FROM DUAL --returns the date in London.
SELECT TO_CHAR(NEW_TIME(SYSDATE, 'CST', 'GMT'),'HH24:MI') FROM DUAL --returns the time, based on the 24-hour clock, in London.
SELECT TO_CHAR(NEW_TIME(SYSDATE + (14 / 24), 'PST', 'PST'),'DD-MON-YY HH24:MI') FROM DUAL --returns the date and time in China.
SELECT TO_CHAR(NEW_TIME(SYSDATE + (diff / 24), ‘GMT’, ‘GMT’),’DD-MON-YY HH24:MI’) FROM DUAL; --returns the date and time of your office.

Answer 2

Have you compared the NLS_DATE_FORMAT on your local machine and the server? You may find that a combination of differences in this, and the possibility that an impicit conversion is happening when the date is being passed in may be your problem here.

Answer 3

The function as written does not work when the session calling it does not have the time zone information set. Therefore, you need to explicitly specify the source time zone. The following function solves this problem (and corrects the return type):
function unix_time_from_date
(
in_date in date,
in_src_tz in varchar2 default 'America/New_York'
)
return integer
as
ut integer := 0;
tz varchar2(8) := '';
tz_date timestamp with time zone;
tz_stmt varchar2(255);
begin
-- Get the local time zone abbreviation from the passed in date
tz_stmt := 'select systimestamp at time zone ''' || in_src_tz || ''' from dual';
execute immediate tz_stmt into tz_date;
select
extract(timezone_abbr from tz_date)
into tz
from dual;
-- Get the Unix timestamp
select
(new_time(in_date, tz, 'GMT') - to_date('01-JAN-1970', 'DD-MM-YYYY')) * (86400)
into ut
from dual;
return ut;
end unix_time_from_date;
Note the addition of a second parameter to the function. This parameter, in_src_tz, is used to indicate what time zone the in_date parameter is in. The value of in_src_tz should be one of the timezone listed in the tzname column of the v$timezone_names table.
Also, you cannot simply select the value of the tzabbrev column in the v$timezone_names table due to time zone having multiple abbreviations. By using the extract, you will get the current abbreviation with DST factored in.