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package org.glassfish.apf;

import org.jvnet.hk2.annotations.Contract;

import java.lang.annotation.Annotation;

/**
 * This interface defines the contract for annotation handlers 
 * and the annotation processing engine. Each annotation handler
 * is registered for a particular annotation type and will be 
 * called by the engine when such annotation type is encountered.
 *
 * The AnnotationHandler is a stateless object, no state should 
 * be stored, instead users should use the ProcessingContext.
 *
 * Annotation can be defined or processed in random orders on a 
 * particular type, however, a particular annotation may need 
 * other annotation to be processed before itself in order to be 
 * processed successfully. An annotation type can indicate through
 * the @see getAnnotations() method which annotation types should 
 * be processed before itself.
 *
 * Each implementation of this interface must specify the annotation that it can handle using
 * {@link AnnotationHandlerFor} annotation.
 *
 * @author Jerome Dochez
 */
@Contract
public interface AnnotationHandler {
    public final static String ANNOTATION_HANDLER_METADATA = "AnnotationHandlerFor";
    
    /**
     * @return the annotation type this annotation handler is handling
     */
    public Class getAnnotationType();
    
    /**
     * Process a particular annotation which type is the same as the 
     * one returned by @see getAnnotationType(). All information 
     * pertinent to the annotation and its context is encapsulated 
     * in the passed AnnotationInfo instance.
     * 
     * @param element the annotation information
     */
    public HandlerProcessingResult processAnnotation(AnnotationInfo element)
        throws AnnotationProcessorException;
    
    /**
     * @return an array of annotation types this annotation handler would 
     * require to be processed (if present) before it processes it's own 
     * annotation type.
     */
    public Class[] getTypeDependencies();
        
}