How do I override Class<?>.getName() for certain classes?

Question

My goal is to be able to override what I get back from CustomClass.class.getName() and CustomClass.getClass().getName()

It should return a custom value, which I think is best to define in an attribute like

@NameOverride("Custom.fully.qualified.class.name")
public class CustomClass {}

Is there any way to do that?

Answer 1

Fred's answer is okay, but his aspect could be somewhat more elegant with less code and especially fewer reflection calls. Sorry, I prefer AspectJ native code style, but @AspectJ annotation style would not be much longer:

String around(Class clazz) : call(public String Class.getName()) && target(clazz) {
    NameOverride nameOverride = (NameOverride) clazz.getAnnotation(NameOverride.class);
    return nameOverride == null ? proceed(clazz) : nameOverride.value();
}

---

Here is the full source code. I added a class without annotation to show the different behaviour and also a restriction to class definitions - @Target(ElementType.TYPE) - to the annotation class. I am also showing package names and imports:

package test;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface NameOverride {
    String value();
}

package test;

public class NormalClass {}

package test;

@NameOverride("Custom.fully.qualified.class.name")
public class CustomClass {}

package test;

public class Main {
    public static void main(String[] args) {
        System.out.println(NormalClass.class.getName());
        System.out.println(CustomClass.class.getName());
        System.out.println(new NormalClass().getClass().getName());
        System.out.println(new CustomClass().getClass().getName());
    }
}

package aspectj;

import test.NameOverride;

public aspect GetNameOverrider {
    @SuppressWarnings({ "unchecked", "rawtypes" })
    String around(Class clazz) : call(public String Class.getName()) && target(clazz) {
        NameOverride nameOverride = (NameOverride) clazz.getAnnotation(NameOverride.class);
        return nameOverride == null ? proceed(clazz) : nameOverride.value();
    }
}

The output:

test.NormalClass
Custom.fully.qualified.class.name
test.NormalClass
Custom.fully.qualified.class.name

Answer 2

This is for sure not the best/fastest solution but maybe a POC...

First of all the file structure:

./src/aspectj:
GetNameOverrider.aj

./src/test:
CustomClass.java    Main.java       NameOverride.java

NameOverride.java:

@Retention(RetentionPolicy.RUNTIME)
public @interface NameOverride {
    String value();
}

GetNameOverrider.aj:

@Aspect
public class GetNameOverrider {
    @Around("call(String getName()) && !within(aspectj..*)")
    public String advice(ProceedingJoinPoint pjp) throws Throwable {

        String ret = (String) pjp.proceed();

        String className = "" + pjp.getTarget();
        className = className.replace("class ", "");
        try {
            test.NameOverride anno = Class.forName(className).getAnnotation(
                    test.NameOverride.class);

            if (anno != null) {
                return anno.value();
            }
        } catch (ClassNotFoundException e) {
            return ret;
        }

        return ret;
    }
}

gives me for Main.java:

public class Main {
    public static void main(String[] args) {
        System.out.println(CustomClass.class.getName());
        System.out.println(new CustomClass().getClass().getName());
    }
}

the output:

Custom.fully.qualified.class.name
Custom.fully.qualified.class.name