Feedback on proposal for #ReflectiveAccessToNonExportedTypes

[Alan Bateman]

On 12/07/2016 10:28, Andrew Dinn wrote:

> :
> I think I need to ask you to clarify this as it doesn't seem to
> recognise the point I was making. Of course, that may well indicate that
> I have failed to understand the precise behaviour of exports dynamic.
>
> Let us assume Module M exports dynamic P, where P is a package which
> contains a public class C_pub and a non-public class C_pri (let's say it
> is package-protected).
>
> My understanding is that this means that:
>
> Java source files for classes not in module M which import these classes
> or reference them by name will suffer a compile-time error.
Correct. Also an error (IllegalAccessError) at run-time if you create 
the bytecode by other means (or maybe dropping the public modifier and 
not re-compiling the compiler for example).

>
> References to the corresponding instances of class Class for C_pub or
> C_pri may nevertheless be obtained by methods of classes not in Module M
> at runtime (e.g. using a classloader lookup by name).
Correct. This is visibility and is not changed (try Class.forName to 
load C_Pri with JDK 8 and you'll see the same thing).

>
> References to members of these classes (methods or fields) may be
> obtained by methods of classes not in Module M (e.g. by using the public
> API of Class).
Correct. However if you attempt access (Method::invoke, Field::get, 
Constructor::newInstance) then it will fail with IllegalAccessException 
(exactly the same as JDK 8 and older).

>
> Calls to setEnabled(true) on those members will succeed even when the
> calling method is not in class M (assuming the call is not invalidated
> by the usual (mon-module) security restrictions)
I assume you mean setAccessible(true), the sledge hammer that breaks the 
door down by suppressing Java Language access checks. In this case, 
package P is exported, and so setAccessible(true) will succeed.

>
> The latter is so irrespective of whether we are referring to class C_pub
> or C_pri and irrespective of whether the member of C_pub or C_pri in
> question is public or non-public.
If a library or framework really needs to get at types or members that 
aren't accessible then this is what it will typically too. There are 
sometimes better solutions with Lookup objects but maybe the discussion 
will go there. For now I assume we need to establish the basics.

-Alan