[improve][broker] Replace String.intern() with Guava Interner

[lhotari]

Motivation

It is not recommended to use String.intern() at all. Guava contains a better replacement in it's Interner class.

Gradle build tool has been using Guava's interner for years (since it was introduced in 2015 with gradle/gradle@799e03e6) and it has been a successful solution in reducing String instance duplication without the problems that String.intern() has.

Modifications

Replace String.intern() with the singleton instance that uses Guava Interner

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

[tisonkun]

might cause memory leaks outside of DoS attacks since the instances will never be collected by GC

Can you provide evidence of this statement? I'm surprised if it's the case it should be a JDK bug. And the original PR introduced these lines #952 used it to reduce String objects.

[lhotari]

might cause memory leaks outside of DoS attacks since the instances will never be collected by GC

Can you provide evidence of this statement? I'm surprised if it's the case it should be a JDK bug. And the original PR introduced these lines #952 used it to reduce String objects.

@tisonkun String intern seemed to have improved in JDK 8 and my knowledge about that was outdated. I was wrong about "never be collected by GC". Interned String instances will get collected as the last resort, in Full GC.
I'll remove the DoS argumentation from the PR description. However, as I mentioned, Guava's Interner is a very well optimized solution for interning objects. It has been used in Gradle since 2015 and it's very performant.

[tisonkun]

Thanks for your explanation :D