RFR: 8350880: (zipfs) Add support for read-only zip file systems [v12]

[Xueming Shen]

On Wed, 21 May 2025 23:30:18 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:
> 
>   More tweaking...

Looks like I'm late to the party :-) My apologies if this has already been discussed a long time ago. My question is whether it's really necessary to restrict the 'read-only' flag to existing ZIP files only. I don't see any issue with allowing the creation of a new, empty ZIP file and marking it as read-only. Sure, it might be useless since it's just an empty zip file system, but that's up to the user.  Not a very strong opinion though.

283  *           <li>
284  *               If the value is {@code "readOnly"}, the file system is created
285  *               <em>read-only</em>, and {@link java.nio.file.FileSystem#isReadOnly()
286  *               isReadOnly()} will always return {@code true}. Creating a
287  *               <em>read-only</em> file system requires the underlying ZIP file to
288  *               already exist.
289  *               Specifying the {@code create} property as {@code true} with the
290  *               {@code accessMode} as {@code readOnly} will cause an {@code
291  *               IllegalArgumentException} to be thrown when creating the ZIP file
292  *               system.
293  *           </li>

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PR Comment: https://git.openjdk.org/jdk/pull/25178#issuecomment-2906012555