Java注释处理器是否能够删除注释的代码

Question

As we all know, we can automagicaly generate code using custom annotations and Java annotation processors as guys at project Lombook do. But can we remove the annotated code from compiled sources ?

I've tried searching the web for it, but only things that appear are "generate your code" topics and tutorials on "how to generate server with one annotation". It came to my mind while I was searching for ways to "compile out" debug messages from prod app. I can understand, that having the debug/test and production code is not a good practice, but sometimes it is needed to keep things simple. I think of few scenarios for this:

1. make debug only, laggy code used in developer-only version of code that can have different levels of importance for example:

@Debug(0) void cpuLightFunction(){}
@Debug(100) void cpuHeavyFunction(){} 

void doWork(){
   cpuLightFunction();
   cpuHeavyFunction();
}

In annotation processing step we could use some option to define max level of @Debug annotations that would be compiled. Any usage of @Debug with higher level would produce error or warning in the same way as @Deprecated

2. platform specyfic code versions - create custom @Platform(ANDROID) void doSomething() and @Plaform(IOS) void doSomething functions that run only on given plaform to get rid of polymorphic void doSomething(AndroidPlatform) or void doSomethingAndroid() code

3. have parts of code that are conditionally compiled:

@Optional("NetworkStub")
class NetworkStub{
   // ...
}

@Optional("PaymentStub")
class PaymentStub{
   // ...
}

and only use compiler/annotation processor options to enable/disable parts of the code, for example -Aoptional="NetworkStub" that would only compile code related to NetworkStub in the code and remove all code touching PaymentStub.

Answer 1

You can do this by writing an annotation processor that traverses and modifies the program's AST (abstract syntax tree) during compilation, before code generation.

That is how Project Lombok works.

This question is a near-duplicate of How to write a Java annotation processor? , but the accepted answer to that question says it's impossible, which is factually wrong.