d6a7aefd1d
Unfortunately, it is not possible to raise the byte code level beyond
Java 1.8 for classes generated using CGLIB due to the fact that CGLIB
generates STATICHOOK methods which set static final fields outside the
initializer method <clinit> (i.e., a static initialization block).
Attempting to raise the level to Java 17 (or even Java 9) results in
exceptions like the following.
Caused by: java.lang.IllegalAccessError: Update to static final field
org.example.MyBean$$SpringCGLIB$$0.CGLIB$THREAD_CALLBACKS attempted from
a different method (CGLIB$STATICHOOK1) than the initializer method <clinit>
at org.example.MyBean$$SpringCGLIB$$0.CGLIB$STATICHOOK1(<generated>)
at org.example.MyBean$$SpringCGLIB$$0.<clinit>(<generated>)
This commit therefore introduces inline comments pointing out why we
stay with Java 1.8 byte code level with CGLIB.
See gh-34602
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