Re: Method.getMethod for varargs?

On 11/30/2017 4:20 AM, [email protected] wrote:
> Hi,
> 
> I'm new to using ASM and I'm trying to look up some method with varargs and I
> don't understand how to format the string input to getMethod to match the
> actual signature.
> 
> I'm calling getMethod like this:
>          method = Method.getMethod(stringArg);
> 
> The method I want to inspect is declared in the code as:
>    void log(Foo foo, Object... bar);
> 
> When I pass in "stringArg" as
>     void log(mypackagage/Foo, [java/lang/Object)
> I get back a Method where getDescriptor() returns this
>     (Lmypackage/Foo;[Ljava/lang/Object;)V
> 
> If I make a MethodVisitor and look how the "desc" argument in the
> visitMethodInsn(int opcode, String owner, String name, String desc, boolean
> itf) looks like when visiting the "log" method, "desc"  looks like this:
>     (Lmypackage/Foo;L[java/lang/Object;)V
> 
> That is, the former has "[L" and the latter has "L[" for the varargs; I'm
> obviously doing this wrong.
> 
> I've tried calling getMethod with the bracket at the end:
>     void log(mypackagage/Foo, java/lang/Object[)
> and then my method gets the signature
>    (Lmypackage/Foo;Ljava/lang/Object[;)V
> Which still isn't a match with what I see in the visitor.
> 
> So what should I pass in to get the description with "L["?

The usual Java Method.getMethod takes a String name for the name of the
method, e.g., "log", and zero or more Class objects for the types of the
arguments.  These would be written Foo.class and Object[].class.

At the bytecode level, according to javap, the descriptor is:
  "(Lmypackage/Foo;[Ljava/lang/Object;)V"

That should definitely match some method on the ASM side.  Since the ...
stuff turns into an array type during compilation, ASM is not going to
do anything special with it.  [L etc. is the correct form; L[ should
not occur.  So I don't really have an answer.  Either something is
pretty broken or you're reading that descriptor incorrectly ...

Regards - Eliot Moss


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