issue with full list copies in pekko-stream javadsl

[pjfanning]

see #1488

[samueleresca]

Few questions:

• should we create a follow-up issue to update the rest of the code to use the new CollectionUtil?
• Is it worth updating the existing documentation of the immutableSeq method to point to the new CollectionUtil object?

Otherwise looks good to me.

[pjfanning]

Few questions:

• should we create a follow-up issue to update the rest of the code to use the new CollectionUtil?
• Is it worth updating the existing documentation of the immutableSeq method to point to the new CollectionUtil object?

Otherwise looks good to me.

CollectionUtil is package private. I think there is a tradeoff between having centralised code but then also meaning that many Pekko libs require a minimum version of a shared Pekko lib like pekko-actor.
I looked at the other usages of Util.immutableSeq(java.util.List) in this repo and in pekko-http and they don't really seem to be in performance critical paths. Some of the changes in this PR are in performance critical paths for Java DSL users.

[samueleresca]

Few questions:

• should we create a follow-up issue to update the rest of the code to use the new CollectionUtil?
• Is it worth updating the existing documentation of the immutableSeq method to point to the new CollectionUtil object?

Otherwise looks good to me.

CollectionUtil is package private. I think there is a tradeoff between having centralised code but then also meaning that many Pekko libs require a minimum version of a shared Pekko lib like pekko-actor. I looked at the other usages of Util.immutableSeq(java.util.List) in this repo and in pekko-http and they don't really seem to be in performance critical paths. Some of the changes in this PR are in performance critical paths for Java DSL users.

Thanks for clarifying.