Re: RFR:8143413:add toEpochSecond methods for efficient access

Tue, 01 Dec 2015 06:23:43 -0800 

Hi Sherman,

On 11/30/2015 6:09 PM, Xueming Shen wrote:

On 11/30/2015 01:26 PM, Stephen Colebourne wrote:

Converting LocalDate<-> java.util.Date is the question with the
largest number of votes on SO:
http://stackoverflow.com/questions/21242110/convert-java-util-date-to-java-time-localdate/21242111 
The proposed method is designed to make the conversion easier. It also
plugs an obvious gap in the API.

While the LocalTime/OffsetTime methods are of lower importance, not
having them would result in inconsistency between the various classes.
We've already added factory methods to LocalTime for Java 9, these are
just the other half of the picture.



I'm not sure I understand the idea of "the proposed method is designed to
make the conversion easier", as the SO is mainly about j.u.Date->LocalDate, 
not the other way around, from LocalDate -> j.u.Date.
I think the issue is about *other* libraries that manipulate time via epochSeconds not about j.u.Date conversions. The concern was about performance and creating garbage along the way. 

Roger
As I said in the previous email, it might be "common" to use the j.u.Date to abstract a "local date" and/or a "local time" (no other choice) before java.time, and now there is the need to provide a migration path from those "local date/ time" to the j.t.LocalDate/Time. But convert backward from the new date/time type to the "old" j.u.Date should not be encouraged (guess this is also the 
consensus we agreed on back to jsr203).
What are the "factory methods" you are referring to here? JDK-8133079, The 
LocalDate/LocalTime.ofInstant()?
(btw, these two methods see missing the "since 1.9/9" tag)
It seems to me that the ofInstant(Instant, ZondId) is from a "super-set" of date/time to a "sub-set", without any assumption of "default value", it is 
similar to the conversion from zdt->ldt->ld/lt, and I can see the "small"
improvement

from|
Date input = new Date();
LocalDatedate =input.toInstant().atZone(ZoneId.systemDefault()).toLocalDate();| 

to
|LocalDatedate =LocalDate.ofInstant(input.toInstant(),ZoneId.systemDefault()));|
The proposed pair toEpochSecond() however is doing the other way around and with an unusual assumption of the missing date/time piece to a "default value" 
(midnight, the epoch day).

personally I think

localDate.atTime(LocalTime.MIDNIGHT).toEpochSecond(ZoneOffset);
localTime.atDate(LocalDate.EPOCHDATE).toEpochSecond(ZoneOffset);
is clean and good enough to help this backward conversion (with the addition 
of LocalDate.EPOCHDATE/DAY constant). Maybe, the vm can even help to
remove that LocalDateTime middle man, with some arrangement.

-Sherman


Note that these methods are specifically not referencing
java.util.Date itself. Epoch seconds is the appropriate intermediate
form here, and still widely used.

Stephen
On 30 November 2015 at 19:36, Xueming Shen<xueming.s...@oracle.com> wrote: 
On 11/30/2015 10:37 AM, Stephen Colebourne wrote:

This is based on user difficulties picked up via Stack Overflow. These
methods aim to provide a simpler and faster approach, particularly for
cases converting to/from java.util.Date.

Can you be a little more specific on this one? We now have Instance<=>
Date,
and considerably we might add LocalDateTime<=>  Date with an offset, if
really
really desired (for performance? to save a Instant object as the bridge?). 
But I'm
a little confused about the connection among LocalDate/LocalTime, epoch
seconds
and j.u.Date here. Are you saying someone wants to convert

j.t.LocalDate ->  epoch seconds ->  j.u.Date
j.t.LocalTime ->  epoch seconds ->  j.u.Date
and uses the converted j.u.Date to represent a local date (date with time 
part to
be 0) and/or the local time (with year/month/day to be epoch time) in the 
"old"
system which only has j.u.Date, and has to use the j.u.Date to abstract the 
"local
date" and "local time"?

I think we agreed back to JSR310 that we don't try to add such kind of
"bridge/
convenient/utility" methods into the new java.time package, but only in the old date/calendar classes, if really needed. So if these methods are only to 
help
migrate/bridge between the "old" and "new" calendar systems, the java.time 
might not be the best place for them?


For the time cases, the convention of 1970-01-01 is natural and
commonly used in many codebases.
I'm not sure about that, especially the "natural" part. It might be "common" 
in
the old days if you only have j.u.Date", and might be forced to use
1970-01-01
to fill in the "date" part even when you are really only interested in
"time" part
of it in your app. One of the advantage of java.time.LDT/LD/LT is now we 
have
separate abstract for these different need, I don't see the common need of 
having a LocalTime only meas the "local time" of 1970-01-01, or I
misunderstood
something here.

-Sherman




Stephen



On 30 November 2015 at 18:15, Xueming Shen<xueming.s...@oracle.com>
wrote:

Hi,

While it is kinda understandable to have LocalDate.toEpochSecond(...)
to get the epoch seconds since 1970.1.1, with the assumption of the
time is at the midnight of that day. It is strange to have the
Local/OffsetTime
to have two public methods with the assumption of the "date" is at epoch 
year/month/day. What's the use case/scenario for these two proposed
methods?

-Sherman


On 11/30/2015 06:36 AM, Stephen Colebourne wrote:
The method Javadoc (specs) for each of the three new methods needs to 
be enhanced.

For the date ones it needs to say
"The resulting date will have a time component of midnight at the
start of the day."

For the time ones it needs to say
"The resulting time will be on 1970-01-01."

Some of the line wrapping in the tests looks like it is not indented
correctly.

Otherwise looks fine,
thanks
Stephen
On 30 November 2015 at 11:50, nadeesh tv<nadeesh...@oracle.com> wrote: 
Hi all,

Please review a fix for

Bug Id -https://bugs.openjdk.java.net/browse/JDK-8143413

Issue - add toEpochSecond methods for efficient access

webrev - http://cr.openjdk.java.net/~ntv/8143413/webrev.01/

-- Thanks and Regards,
Nadeesh TV



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