setAccessible() alternative with Jigsaw

Claes Redestad claes.redestad at
Fri Mar 31 13:55:34 UTC 2017

Hi Matej,

there's a recent addition in Lookup.defineClass which might fit your need,



On 03/31/2017 03:46 PM, Matej Novotny wrote:
> Hello,
> I work on Weld, context dependency injection framework.
> Long story short - we need to generate proxies for classes - bytecode which we then "register" with the class loader using java.lang.ClassLoader#defineClass.
> Obviously, for this you need reflections - to load java.lang.ClassLoader, then to load the method itself, and most importantly, to make the method accessible cause it's `protected`.
> In JDK 9, this blows up as soon as you try to make the method accessible (invocation of setAccessible).
> Fair enough, but what is the "legitimate" alternative?
> I know I can --add-opens  / --add-opens / --permit-illegal-access
> But all those just bypass the checks and don't really solve it. I am looking for an intended way to do such stuff.
> I am pretty sure there are many frameworks which need to do this in one way or the other.
> So far I have found workarounds which involve using `sun.misc.Unsafe` because there (for some reason) you are allowed to invoke setAccessible().
> Is this the official intended backdoor? Because it sure does not look any safer/cleaner solution than the original one...
> Any thoughts appreciated
> Matej

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