Creating validator engines

hyphenType comes with two validator engines: CustomizableValidator and BooleanValidator. Although these two validators are highly customizable, it is possible that you may want to create your own validator engine.

Creating your own validator engine is relatively easy. All you need to do is to create a class that implements the ArgumentsProcessorEngine interface, and follow some simple rules.

As with documentation formatters, validator engines comprise two entities: the annotation and the engine itself.

1. validator annotation - The anotation that will decorate an options interface. This annotation should contain all properties that will configure the validator.
2. validator engine - Contains the logic that will check the options interface based on the configuration provided in to the annotation.

Here are the rules a validator engine should follow. We will use the naming convention XEngine for the validator engine and X for the validator annotation.

1. XEngine should have an inner annotation called X.
2. XEngine should implement the ArgumentsProcessorEngine interface and should parameterize the ArgumentsProcessorEngine type using X:

   public class XEngine implements ArgumentsProcessorEngine<XEngine.X>

   A direct consequence of this rule is that X should have a method with the following signature:

   @Override
   public <T extends Options<?>> void process(Class<T> interfaceClass, T options, X config)

   Note that the instance of X is called "config" for a reason. This instance in fact holds the configuration for XEngine.

   Having the @Override annotation is not mandatory but is a good practice.

3. XEngine should have a no-argument constructor, or the default constructor.

   In case you are wondering, yes, there is a difference between those two constructors: http://docs.oracle.com/javase/specs/jls/se7/html/jls-8.html#jls-8.8.9

   This difference is irrelevant here. What is relevant is that if you explicitly add a constructor that accepts any argument to X, you will have no default constructor. Then you will need to correct this problem by adding a non-argument constructor to X.

4. When the validator finds anything wrong during the execution of process(), it should call one of the exit methods in the config object.

Please check the source code of CustomizableValidator for an example of a validator source code.