Re: Java 8 java.time support in FreeMarker 2

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Friday, January 20, 2017, 11:14:32 AM, Geoffrey De Smet wrote:

>> I was thinking about how to support the time API introduced in Java 8
>> (JSR-310). It's on the Contributors Wanted page for a long time, and
>> now we also have a Jira request for it
>> (https://issues.apache.org/jira/browse/FREEMARKER-35).
>>
>> (There's also this: https://github.com/amedia/freemarker-java-8 This
>> doesn't expose the Java API of the objects, but add a few own methods,
>> most importantly "format".)
>>
>> I think that we shouldn't support the java.time types specifically. We
>> hardly want to add 12+ new TemplateModel-s for them
>> (InstantTemplateModel, DurationTemplateModel, LocalDateTemplateModel,
>> MonthDayTemplateModel, etc.), and I think that a such complex and
>> platform specific thing shouldn't be part of the FTL type system
>> anyway. Consistently with that decision, we wouldn't replicate the
>> methods of these things with built-ins either (especially as templates
>> mostly only meant to display these objects). So java.time objects
>> should just fall into the same category as any random application
>> specific class. Thus the DefaultObjectWrapper will expose their Java
>> API-s too, so you can automatically write someLocalDate.year or even
>> someLocalDate.plusDays(1). (Out-of-the-box you won't be able to pass
>> in enums though...) What this so far doesn't solve is formatting. For
>> that, we should improve on how one can format objects of any "random"
>> class. So the user should be able to configure FM so that instances of
>> an user-specified class can be formatted with ?string(...), and also
>> can have a default format specified (similarly to number_format,
>> date_format, etc.). So it's the same logic that we have for numbers
>> and pre-java-8 date-s, only extended to any classes.
>>
>> We still have to "cheat" a bit. If FreeMarker runs on Java 8, it
>> should pre-configure itself to deal with those 12+ java.time classes
>> (otherwise the user had to copy-paste some long configuration
>> fragment). Also we should add a few variation of `.now` that returns
>> the value with Java 8 types.
>>
>> What do you think about this approach?
>
> I think you only need 1 new class: TemporalTemplateModel (or 
> TemporalAccessorTemplateModel), not 12+.
>
> All those 12+ java.time objects implement the interface Temporal and 
> TemporalAccessor.
> For example, LocalDate implements Temporal and TemporalAccessor
> DateTimeFormatter is the class to parse and format (so read and write)
> any of those 12 temporal types.
>
> Writing any such type is easy with 
> DateTimeFormatter.format(TemporalAccessor):
> DateTimeFormatter dateTimeFormatter = 
> DateTimeFormatter.ofPattern("yyyy-MM-dd hh:mm:ss")
> // Landed on moon on 1969-07-20
> String s1 = "Landed on moon on " + 
> dateTimeFormatter.format(LocalDate.of(1969,7,20));
> // Landed on moon at 1969-07-20 20:18
> String s2 = "Landed on moon at " + 
> dateTimeFormatter.format(LocalDateTime.of(1969,7,20,20,18);
>
>
> https://docs.oracle.com/javase/8/docs/api/java/time/LocalDate.html
>
> https://docs.oracle.com/javase/8/docs/api/java/time/temporal/Temporal.html
>
> https://docs.oracle.com/javase/8/docs/api/java/time/format/DateTimeFormatter.html
>
>
>
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-- 
Thanks,
 Daniel Dekany


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