如何使用注释来表示参数化类型？

Question

I trying to using annotation processor to generate some methods like that:

void result(Consumer<Type> name){

}

Than I need to using a annotation to represent a parameter.

@Retention(RetentionPolicy.SOURCE)
public @interface Parameter {

  String name();

  Class<?> type();
}

But the annotation members only support compile-time constants, so it is impossible to delivery a parameterized type directly, for example the following illegal java code can't be represent by annotation.

@Parameter(name ="ids",type = ArrayList<Integer>.class)

I tried to declare a new annotation to represent the type, because the generic parameters can be one or more and nested, such as ArrayList <HashMap <String, String >> , but java does not support annotations reference itself, it will cause cyclic annotation element type error. the following annotation is illegal too.

public @interface Type{
  Class<?> type();
  Type[] parameters() default {};
}

@Retention(RetentionPolicy.SOURCE)
public @interface Parameter {

  String name();

  Type type();
}

Any solutions?

Answer 1

When you cannot represent a value as an annotation argument, the standard solution is to use a string instead. For example, instead of @Parameter(..., type = ArrayList<Integer>.class) , use @Parameter(..., type = "ArrayList<Integer>") , which can represent arbitrarily-nested parameterized types.

Your code that uses the annotations must do parsing and validation of the String argument.