001/*
002 * Namespace.java July 2008
003 *
004 * Copyright (C) 2008, Niall Gallagher <niallg@users.sf.net>
005 *
006 * Licensed under the Apache License, Version 2.0 (the "License");
007 * you may not use this file except in compliance with the License.
008 * You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or 
015 * implied. See the License for the specific language governing 
016 * permissions and limitations under the License.
017 */
018
019package org.simpleframework.xml;
020
021import java.lang.annotation.Retention;
022import java.lang.annotation.RetentionPolicy;
023
024/**
025 * The <code>Namespace</code> annotation is used to set a namespace
026 * on an element or attribute. By annotating a method, field or 
027 * class with this annotation that entity assumes the XML namespace
028 * provided. When used on a class the annotation describes the
029 * namespace that should be used, this however can be overridden by
030 * an annotated field or method declaration of that type.
031 * <pre>
032 *  
033 *    &lt;book:book xmlns:book="http://www.example.com/book"&gt;
034 *       &lt;author&gt;saurabh&lt;/author&gt;
035 *       &lt;title&gt;example title&lt;/title&gt;
036 *       &lt;isbn&gt;ISB-16728-10&lt;/isbn&gt;
037 *    &lt;/book:book&gt;
038 *
039 * </pre>
040 * In the above XML snippet a namespace has been declared with the
041 * prefix "book" and the reference "http://www.example.com/book". If
042 * such a namespace is applied to a class, method, or field then 
043 * that element will contain the namespace and the element name will
044 * be prefixed with a namespace qualifier, which is "book" here.
045 * <pre>
046 *
047 *    &lt;example xmlns="http://www.example.com/root"&gt;
048 *       &lt;child&gt;
049 *          &lt;text xmlns=""&gt;text element&lt;/text&gt;
050 *       &lt;/child&gt;
051 *    &lt;/example&gt;
052 *
053 * </pre>
054 * In order for a namespace to be inherited it must be specified as
055 * a default namespace. A default namespace is one that does not have
056 * a prefix. All elements that do not have an explicit namespace will
057 * inherit the last default namespace in scope. For details see
058 * <a href='http://www.w3.org/TR/xml-names/#defaulting'>Section 6.2</a>
059 * of the namespaces in XML 1.0 specification. To remove the default
060 * namespace simply specify a namespace with no prefix or reference,
061 * such as the "text" element in the above example.  
062 *
063 * @author Niall Gallagher
064 */ 
065@Retention(RetentionPolicy.RUNTIME)
066public @interface Namespace {
067
068   /**
069    * This is used to specify the unique reference URI that is used 
070    * to define the namespace within the document. This is typically
071    * a URI as this is a well know universally unique identifier. 
072    * It can be anything unique, but typically should be a unique
073    * URI reference. If left as the empty string then this will
074    * signify that the anonymous namespace will be used.
075    *
076    * @return this returns the reference used by this namespace    
077    */         
078   String reference() default "";
079
080   /**
081    * This is used to specify the prefix used for the namespace. If
082    * no prefix is specified then the reference becomes the default
083    * namespace for the enclosing element. This means that all 
084    * attributes and elements that do not contain a prefix belong
085    * to the namespace declared by this annotation.
086    *
087    * @return this returns the prefix used for this namespace
088    */ 
089   String prefix() default "";
090}