import com.sun.xml.bind.marshaller.NamespacePrefixMapper;

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class NamespacePrefixMapperImpl extends NamespacePrefixMapper {

    /**
     * Returns a preferred prefix for the given namespace URI.
     * 
     * This method is intended to be overrided by a derived class.
     * 
     * @param namespaceUri
     *      The namespace URI for which the prefix needs to be found.
     *      Never be null. "" is used to denote the default namespace.
     * @param suggestion
     *      When the content tree has a suggestion for the prefix
     *      to the given namespaceUri, that suggestion is passed as a
     *      parameter. Typicall this value comes from the QName.getPrefix
     *      to show the preference of the content tree. This parameter
     *      may be null, and this parameter may represent an already
     *      occupied prefix. 
     * @param requirePrefix
     *      If this method is expected to return non-empty prefix.
     *      When this flag is true, it means that the given namespace URI
     *      cannot be set as the default namespace.
     * 
     * @return
     *      null if there's no prefered prefix for the namespace URI.
     *      In this case, the system will generate a prefix for you.
     * 
     *      Otherwise the system will try to use the returned prefix,
     *      but generally there's no guarantee if the prefix will be
     *      actually used or not.
     * 
     *      return "" to map this namespace URI to the default namespace.
     *      Again, there's no guarantee that this preference will be
     *      honored.
     * 
     *      If this method returns "" when requirePrefix=true, the return
     *      value will be ignored and the system will generate one.
     */
    public String getPreferredPrefix(String namespaceUri, String suggestion, boolean requirePrefix) {
        // I want this namespace to be mapped to "xsi"
        if( "http://www.w3.org/2001/XMLSchema-instance".equals(namespaceUri) )
            return "xsi";
         
        // I want the namespace foo to be the default namespace.
        if( "http://www.example.com/foo".equals(namespaceUri) )
            return "";

        // and the namespace bar will use "b".
        if( "http://www.example.com/bar".equals(namespaceUri) )
            return "b";
            
        // otherwise I don't care. Just use the default suggestion, whatever it may be.
        return suggestion;
    }
    
    
    
    /**
     * Returns a list of namespace URIs that should be declared
     * at the root element.
     * <p>
     * By default, the JAXB RI produces namespace declarations only when
     * they are necessary, only at where they are used. Because of this
     * lack of look-ahead, sometimes the marshaller produces a lot of
     * namespace declarations that look redundant to human eyes. For example,
     * <pre><xmp>
     * <?xml version="1.0"?>
     * <root>
     *   <ns1:child xmlns:ns1="urn:foo"> ... </ns1:child>
     *   <ns2:child xmlns:ns2="urn:foo"> ... </ns2:child>
     *   <ns3:child xmlns:ns3="urn:foo"> ... </ns3:child>
     *   ...
     * </root>
     * <xmp></pre>
     * <p>
     * If you know in advance that you are going to use a certain set of
     * namespace URIs, you can override this method and have the marshaller
     * declare those namespace URIs at the root element. 
     * <p>
     * For example, by returning <code>new String[]{"urn:foo"}</code>,
     * the marshaller will produce:
     * <pre><xmp>
     * <?xml version="1.0"?>
     * <root xmlns:ns1="urn:foo">
     *   <ns1:child> ... </ns1:child>
     *   <ns1:child> ... </ns1:child>
     *   <ns1:child> ... </ns1:child>
     *   ...
     * </root>
     * <xmp></pre>
     * <p>
     * To control prefixes assigned to those namespace URIs, use the
     * {@link #getPreferredPrefix} method. 
     * 
     * @return
     *      A list of namespace URIs as an array of {@link String}s.
     *      This method can return a length-zero array but not null.
     *      None of the array component can be null. To represent
     *      the empty namespace, use the empty string <code>""</code>.
     * 
     * @since
     *      JAXB RI 1.0.2 
     */
    public String[] getPreDeclaredNamespaceUris() {
        return new String[] { "urn:abc", "urn:def" };
    }
}
