How to find out if a class has Jakarta Validation constraints within a byte-buddy plugin

[jafarre-bi]

Hello,

I want to write a byte-buddy plugin to weave in Jakarta Validation into my classes at build time.
The standard and recommended way to find out whether a class contains validation constraints starts with:
Validation.buildDefaultValidatorFactory().getValidator().getConstraintsForClass(Class)
But the plugin only provides a TypeDescription, from which it appears there is no way to obtain the Class.
Can I achieve what I need?

Thanks.

[raphw]

Byte Buddy does not load the class, but parses it to avoid execution of static initializers and the like.

You would need to reimplement the logic of that method. Fortunately, Byte Buddy offers methods with the same names for all properties as the reflection API (with the exception of invoke).

[jafarre-bi]

I guess I could also load the class myself, decide whether it needs to be instrumented and discard it. Do you see any problem with this approach?

[raphw]

No, you can of course load the class path and apply the method.

[jafarre-bi]

So, that's the approach I took, and it looks promising.
This may be out of the scope of the question, but I'm new to Byte-Buddy, and there are still some concepts which aren't totally clear to me.
(By the way, from what I've been able to see until now, Byte Buddy is an amazing piece of great work. Thanks for it!)
My first implementation uses @Advice, which fits my needs, except for the lack of caching when using @Advice.Origin with a parameter of type Method or Constructor. Are there any plans to add caching to this annotation in the same way there is for @Origin? And how would it be different if, instead of Advice, I just used MethodDelegation? My advice is a very simple @OnMethodEnter using @This, @Origin and @AllArguments (I omit Advice. for brevity). Would the resulting code be different if I used method delegation?
Thank you!

[raphw]

You can already cache the value, if you set the corresponding property on the annotation. This does however require adding a field to the instrumented class, what often defeats the purpose of advice.

[jafarre-bi]

There's the cache property in net.bytebuddy.implementation.bind.annotation.Origin, but I can't see such property in net.bytebuddy.asm.Advice.Origin. Am I missing something?

[raphw]

You are right, I did not add an option for that. What you can do instead would be to create your own binding using Advice.withCustomBinding(), where you can use a binding you implement yourself. Here you can easily cache this.

I might add the caching possibility later.

[jafarre-bi]

One more question. I'm using the maven plugin for this. I need to get the path where classes are being looked up to load them. This is, for transform-test, ${project.build.testOutputDirectory}. The easiest way I can think of to get that information is just to pass it as a constructor parameter to the plugin. I've tried several variations of the following:

<transformation>
   <plugin>com.example.MyBuddyPlugin</plugin>
   <arguments>
      <index>0</index>
      <value>${project.build.testOutputDirectory}</value>
   </arguments>
</transformation>

And none of them work. It complains about the lack of a setter for the properties index and value, which are just public attributes with a getter. What am I doing wrong?

[raphw]

Does your plugin define a public constructor with one argument of type String?

[jafarre-bi]

Yes, it complains about the PluginArgument class itself:
Unable to parse configuration of mojo net.bytebuddy:byte-buddy-maven-plugin:1.17.7:transform-test for parameter value: Cannot find default setter in class net.bytebuddy.build.maven.PluginArgument

[jafarre-bi]

Found it. Of the many variations I had tried, I hadn't tried this:

<transformation>
   <plugin>com.example.MyBuddyPlugin</plugin>
   <arguments>
      <argument>
         <value>${project.build.testOutputDirectory}</value>
      </argument>
   </arguments>
</transformation>

Not sure how I missed it. Perhaps because I expected each entry in <arguments> to be a <value>, as happens in some plugins that take lists. The truth is that the error message is a bit misleading. Thanks :)

[jafarre-bi]

Ok, this is working, thanks a lot for your help :)