content: /*
   * Attribute.java July 2006
   *
   * Copyright (C) 2006, 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;
  
  import com.aliyun.odps.simpleframework.xml.transform.Transformer;
  import java.lang.annotation.RetentionPolicy;
  import java.lang.annotation.Retention;
  
  /**
   * The <code>Attribute</code> annotation represents a serializable XML
   * attribute within an XML element. An object annotated with this is
   * typically a primitive or enumerated type. Conversion from the 
   * attribute to primitive type is done with a <code>Transform</code>
   * object. If a suitable transform can be found then this will convert
   * the attribute string value to an object instance, which can be 
   * assigned to the annotated field, or passed to the annotated method.
   * 
   * @author Niall Gallagher
   * 
   * @see Transformer
   */ 
  @Retention(RetentionPolicy.RUNTIME)
  public @interface Attribute {
  
     /**
      * This represents the name of the XML attribute. Annotated fields
      * or methods can optionally provide the name of the XML attribute
      * they represent. If a name is not provided then the field or 
      * method name is used in its place. A name can be specified if 
      * the field or method name is not suitable for the XML attribute.
      * 
      * @return the name of the XML attribute this represents
      */
     String name() default "";
     
     /**
      * This is used to provide a default value for the attribute if
      * the annotated field or method is null. This ensures the the
      * serialization process writes the attribute with a value even
      * if the value is null, and allows deserialization to determine
      * whether the value within the object was null or not.
      * 
      * @return this returns the default attribute value to use
      */
     String empty() default "";
  
     /**
      * Determines whether the attribute is required within an XML
      * element. Any field marked as not required will not have its
      * value set when the object is deserialized. If an object is to
      * be serialized only a null attribute will not appear as XML.
      * 
      * @return true if the attribute is required, false otherwise
      */
     boolean required() default true;   
  }
  