user6719582 user6719582 - 3 months ago 9
Java Question

How to annotate java package and reflect metadata

I would like to annotite java package using simple annotation:

@Target(ElementType.PACKAGE)
public @interface Related {
int apiVersion() default 0;
}


However when I try to add it to any package I've got compilation error

Error:(1, 14) java: cannot find symbol
symbol: class Related
location: package com.test.xxx


Any help appreciated!

EDIT

After searching a bit I found also this kind of error

Error:(1, 1) java: package annotations should be in file package-info.java

Answer

To be able to place annotation on package you should create package-info.java file which should contain package definition like this:

@Related
package tld.some.name;

To be able to reflect reflect package you also need to set up RetentionPolicy.RUNTIME

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.PACKAGE)
public @interface Related {
    // stuff...
}

And then you can finally reflect package:

SomeClassInPackage.class.getPackage().getAnnotation(Related.class)

You can also reflect package by name using java.lang.Package

Package.getPackage("tld.some.name").getAnnotation(Related.class)