Compiling annotations

Introduction

When you are writing your annotation in JavaDoc, you need to post-compile your classes in order to parse the sources, retrieve the JavaDoc annotations, process and validate the annotations and finally put them into the bytecode as regular Java 5 RuntimeVisible annotations.

This is done by using the backport175 compiler, AnnotationC.

AnnotationC compiler

You can run AnnotationC either from the command line or using the Ant task.

You invoke the compiler like this:

java [options...] org.codehaus.backport175.compiler.AnnotationC
     [-verbose]
     -src <path to src dir>
     -classes <path to classes dir>
     [-dest <path to destination dir>]
     [-config <optional property file(s) for annotations>]

The last option -config <property file(s)> points to the (or several files separated by classpath separator - ; or : depending on you OS) property file which defines annotation aliases (or imports) by mapping the names to the fully qualified class names of the annotation interface.

Note that if you are using the -dest option, the anonymous inner classes will not be copied to the destination directory, since the anonymous classes are not taken into account by the annotation compiler. In such a case it is recommended to add the following (if using Ant) just after the call to AnnotationC when the -dest option is used: (adapt according to the directories you are using)

<copy todir="classes/annotated" overwrite="false"> 
    <fileset dir="classes/regular"/> 
</copy>

Annotation definition file

Since the annotations are written in JavaDoc, there is no way of doing imports of the annotations interfaces.

This leaves you two options:

• either you use the fully qualified name of the annotation interface when writing the the annotations, e.g.:

  Code Block
  java
  /** * @org.codehaus.backport175.annotation.OneWay */ public void method() { ... }

  which can be a bit verbose and cumbersome in the long run.

• or you define aliases (shortcuts/abbreviations), for the annotations and map these to the fully qualified class names for the annotation interfaces. This is done using the annotations.properties file.
  Example:

  Code Block
  java
  OneWay = org.codehaus.backport175.annotation.OneWay TwoWay = org.codehaus.backport175.annotation.TwoWay

  If we now feed this property file to the compiler we are able to write the annotations like this instead:

  Code Block
  java
  /** * @OneWay */ public void method() { ... }

Rules for annotation naming consistency

It is important to remember that if you are using an alias through a propery file, the annotation name is still the fully qualified name of the interface class for the annotation when using the Annotations.getAnnotation API.

If you decide to use an alias, then you have to use this alias in the whole sources. It is not possible to use from time to time in the source an alias or the fully qualified name, since backport175 has to ensure an element cannot be annotated twice with the same annotation, as per JSR-175.
If you decide to use the fully qualified name, the same rule applies, it needs to stay consistent.

If the annotation is a nested class like Target.OneWay below, you can use a $ in the name (as when using java.lang.reflect.* API) or a . which can be more readable.
Once again, this choice has to be consistent thus one or the other has to be used accross the code base but not both:

package demo;
/**
 * @demo.Target$OneWay
 */
public class Target {
  public static class OneWay {}
}

or (with dot)

package demo;
/**
 * @demo.Target.OneWay
 */
public class Target {
  public static class OneWay {}
}