FrankChen021 commented on pull request #12232:
URL: https://github.com/apache/druid/pull/12232#issuecomment-1059917494


   > I think there's also some flag that stops these messages from happening:
   > 
   > ```
   > WARNING: An illegal reflective access operation has occurred
   > WARNING: Illegal reflective access by 
com.google.inject.internal.cglib.core.$ReflectUtils$1 
(file:dist/druid/lib/guice-4.1.0.jar) to method 
java.lang.ClassLoader.defineClass(java.lang.String,byte[],int,int,java.security.ProtectionDomain)
   > WARNING: Please consider reporting this to the maintainers of 
com.google.inject.internal.cglib.core.$ReflectUtils$1
   > WARNING: Use --illegal-access=warn to enable warnings of further illegal 
reflective access operations
   > WARNING: All illegal access operations will be denied in a future release
   > ```
   > 
   > I see them on all server startups when running on Java 11. They seem 
harmless but they look scary, like the cops are going to come and toss you in 
jail.
   
   I made an further investigation on this.
   
   Guice to [5.0.1 (see the 
highlights)](https://github.com/google/guice/wiki/Guice501) eliminates this 
warning. 
   But unfortunately, guice 5.0.1 uses some APIs in newer guava, and the lowest 
guava version that is compatible with guice 5.0.1 is 20.0. Currently Druid is 
using guava 16.0.
   
   I noticed that there're some PRs(#11668, #10290, #10683) working on 
upgrading guava to new version, but they were blocked due to compatibility 
problem with hadoop 2.
   
   So, before we upgrade guava to newer version, we can't eliminate this 
warning by upgrading guice. 
   cc @gianm 


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