RFR: 8350880: (zipfs) Add support for read-only zip file systems [v4]

[Jaikiran Pai]

On Thu, 15 May 2025 18:27:35 GMT, David Beaumont <duke at openjdk.org> wrote:

>> Adding read-only support to ZipFileSystem.
>> 
>> The new `accessMode` environment property allows for readOnly and readWrite values, and ensures that the requested mode is consistent with what's returned.
>> 
>> This involved a little refactoring to ensure that "read only" state was set initially and only unset at the end of initialization if appropriate.
>> 
>> By making 2 methods return values (rather than silently set non-final fields as a side effect) it's now clear in what order fields are initialized and which are final (sadly there are still non-final fields, but only a split of this class into two types can fix that, since determining multi-jar support requires reading the file system).
>
> David Beaumont has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Changes based on review feedback.

src/jdk.zipfs/share/classes/jdk/nio/zipfs/ZipFileSystem.java line 114:

> 112:     private final ZipPath rootdir;
> 113:     // Starts in readOnly (safe mode), but might be reset at the end of initialization.
> 114:     private boolean readOnly = true;

If `readOnly` gets used by some code when a `ZipFileSystem` instance is being constructed (which is why I believe this can't be a `final` field), then I think we should not change this value to `true`. In other words, would this change now have a chance of introducing a `ReadOnlyFileSystemException` when constructing the `ZipFileSystem` whereas before it wouldn't?

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PR Review Comment: https://git.openjdk.org/jdk/pull/25178#discussion_r2093154523