content: /*
   * Extractor.java March 2011
   *
   * Copyright (C) 2011, Niall Gallagher <niallg@users.sf.net>
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or 
   * implied. See the License for the specific language governing 
   * permissions and limitations under the License.
   */
  
  package com.aliyun.odps.simpleframework.xml.core;
  
  import java.lang.annotation.Annotation;
  
  /**
   * The <code>Extractor</code> interface is used to represent an object
   * that can be used to extract constituent parts from a union. Using
   * this allows a uniform interface to be used to interface with various
   * different union annotations. 
   * 
   * @author Niall Gallagher
   * 
   * @see ExtractorFactory
   */
  interface Extractor<T extends Annotation>{
     
     /**
      * This is used to acquire each annotation that forms part of the
      * union group. Extracting the annotations in this way allows
      * the extractor to build a <code>Label</code> which can be used
      * to represent the annotation. Each label can then provide a
      * converter implementation to serialize objects.
      * 
      * @return this returns each annotation within the union group
      */
     T[] getAnnotations() throws Exception;
     
     /**
      * Each annotation can provide a class which is used to determine
      * which label is used to serialize an object. This ensures that
      * the correct label is selected whenever serialization occurs.
      * 
      * @param label this is the annotation to extract the type for
      * 
      * @return this returns the class associated with the annotation
      */
     Class getType(T label) throws Exception;
     
     /**
      * This creates a <code>Label</code> object used to represent the
      * annotation provided. Creating the label in this way ensures
      * that each union has access to the serialization methods 
      * defined for each type an XML element name.
      * 
      * @param label this is the annotation to create the label for
      * 
      * @return this is the label created for the annotation
      */
     Label getLabel(T label) throws Exception;
  }