Proposal: JDK-8231640 - (prop) Canonical property storage

[Alan Bateman]

On 24/08/2021 15:07, Jaikiran Pai wrote:
> The java.util.Properties class allows the properties to be written out 
> to a stream or through a writer. In its current form, the 
> specification of these APIs state that a comment comprising of the 
> current date is always written out. The spec doesn't make any 
> guarantees about the order of the properties when they are written out.
>
> There have been requests asking to make these APIs more deterministic. 
> These requests, from what I have seen, mainly ask for:
>
> - A way to disable writing out the date comment
> - A way to write out the properties in a deterministic and 
> reproducible way
>
> There have been discussions in the mailing list in the past which have 
> been captured in JDK-8231640[1]. In these discussions, there has been 
> an inclination to not touch the current existing API implementations 
> and instead introduce new API(s) to achieve the proposed use cases.
>
> Before starting off with an implementation, I wanted to try and get 
> some inputs on what the new API(s) would look like and what the scope 
> of such a work should be.

Another possibility is to add an overload of store that adds a 
java.time.Instant argument for the timestamp. It could be specified as 
Instant.EPOCH where reproducibility is required.

Magnus brings up the possibility of specifying that the store methods 
look for SOURCE_DATE_EPOCH. As it happens, someone tried that [1]. With 
a spec change and the correct implementation then it should be feasible 
option to explore.

We touched on the ordering issue in the jdk-dev discussion in 2019. I 
think that can be changed to write in sorted key order without a spec 
change, although it could be a useful property to specify.

-Alan

[1] https://bugs.openjdk.java.net/browse/JDK-8272157