JEP proposed to target JDK 18: 400: UTF-8 by Default

[Simon Nash]

On 18/08/2021 20:49, Naoto Sato wrote:
> Hi Simon,
>
> Please post your comments at core-libs-dev mailing list, where the discussion should take place.
>
> Naoto
>
My apologies that I am late into the discussion of this JEP.

I am the developer of a fairly large application that uses file I/O extensively. In most cases, the charset should be UTF-8 and I have used an explicit charset 
parameter on all method invocations where this applies. In some cases, the charset needs to be the platform default charset to produce output that is readable 
by other programs or by a user (for example, Windows-1252 on some versions of Windows).

In the cases that need the platform default charset, I have omitted the charset (intentionally, not carelessly or accidentally). If the behaviour changes in 
these cases, it will produce unexpected results for users.

I could try to find all the method invocations that currently use the implicit default charset, although I have no idea how to do this other than reading every 
line of code. The problems with this are 1) that I would almost certainly miss some invocations that need to be changed and 2) more seriously, from what I have 
seen in the JEP I don't think there is a way to update these method invocations that works exactly as at present on all versions of Java back to JDK 8 and 
provides the same behaviour on JDK 18. This is because (as far as I can tell) there is no API call that returns the "old-style" platform default charset and can 
be used on all JDK versions from JDK 8 to JDK 18. Adding a -D option when the application is started isn't possible in some contexts such as launching the 
application from a Windows executable jar file association.

If I could make a single API call when the application is first started to force backward-compatible behaviour in all cases, this would solve the problem. This 
feels very much like a "hack" and I would much prefer a clean solution but it would be better than nothing.

Does this JEP provide some way to do what I need?

Simon