RFR: 8312630: java/security should not create unmodifiable collections with redundant wrapping

[Xue-Lei Andrew Fan]

On Wed, 26 Jul 2023 06:11:56 GMT, Xue-Lei Andrew Fan <xuelei at openjdk.org> wrote:

>> Some java/security classes apply the below coding style,
>> 
>> Set<T> set = ...;
>> Set<T> unmodifiableSet = Collections.unmodifiableSet(new HashSet<>(set));
>> 
>> It may be unnecessary to wrap that `set` with HashSet before creating `unmodifiableSet`.
>> Some usages on `Collections.unmodifiableList` and `Collections.unmodifiableMap` have the same issue.
>
> Note: Please don't backport this update unless [JDK-6323374](https://bugs.openjdk.org/browse/JDK-6323374) is backport as well.

> @XueleiFan Thanks for your review and more infos!
> 
> I just dug a bit history and found [JDK-8258514](https://bugs.openjdk.org/browse/JDK-8258514) applied `List::copyOf` instead of `Collections::unmodifiableList`. Now, I also follow this way and use `List/Set/Map::copyOf`.

The use of copyOf for the update is mainly because the Collections::unmodifiableList was not updated yet at that time.  It could be simpler to keep the behavior consistent by using Collections::unmodifiableList in this update.  Otherwise, more effect may be required to check if the use of copyOf could change the behaviors.

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PR Comment: https://git.openjdk.org/jdk/pull/15008#issuecomment-1652370187