AVal: Annotation Validation

AVal is an extendable meta-annotation based Annotation Validator for java 5. It provides a set of basic validation rules, as well as means to define more domain-specific ones.

AVal Latest (Beta) Release:

 AVal 1.0b - Columbo -- release notes

 AVal 0.7 - Grissom -- release notes

 AVal 0.5b - Poncharello -- release notes --  readme

 AVal 0.1a - Clouseau -- release notes

Table of contents

  1. Who is AVal for?
  2. What is AVal?
  3. How to use AVal
  4. Built-in Validations
  5. Examples
  6. Architecture

Who is AVal for?

AVal is intended for framework programmers that use Java 5 annotations to express domain-specific concepts and need an expressive, declarative and self documenting way to encode the rules of use of their annotations.

What is AVal

AVal is an extendable meta-annotation based Annotation Validator for java 5. It provides a set of basic validation rules, as well as means to define more domain-specific ones.

AVal allows you to embed the way in which the annotations defined in your framework are to be validated. It can be seen as an extension of the @Target annotation provided in the Java5 JDK. An example of an AVal validated annotation would be: 

@Inside(Web.class)
@AValTarget(CtMethod.class)
@Type(void.class)
public @interface Link {
   @URLValue 
   String value();
}

How to use AVal

To use AVal it is enough to annotate your (base)annotations with some meta-annotations that define the way in which your annotations should be used.

Some of the build-in validations in AVal

Structural Validations

@Requires
States that a code element (for example a class) that is annotated by an Annotation, must also be annotated by another one.
@AValTarget
States on which code elements can an annotation be placed. This is a refinement from the Target Java5 annotation.

... more

Value Validations

@Matches
Restricts the values of an Annotation's attribute to only the ones that comply with a given regular expression.
@URLValue
States that the values of an Annotation's attribute must be valid URLs.

... more

A complete list of the available @Validators can be seen here and here.

Examples

(source for all these examples can be found in the Downloads? page)

  1. AVal.SimpleExample: A simple example
  2. AVal.ExampleFraclet:Validation of Fraclet annotations
  3. AVal.ExampleWebService: Validation of JSR181 annotations.

Architecture

AVal is completely based on annotations. There are 4 basic layers to AVal:

  1. Base program: The target program
  2. DSL Annotations: The annotations that implement domain-specific semantics.
  3. Validation Annotations: Meta-annotations that validate the DSL (see here for some examples)
  4. Implementation of Validation: The semantics of the Validation annotations

See the javadoc here

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