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Stax2 API is an extension to basic Stax 1.0 API that adds significant new functionality, such as full-featured bi-direction validation interface and high-performance Typed Access API.

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package org.codehaus.stax2.ri;

import java.util.Iterator;

import javax.xml.XMLConstants;
import javax.xml.namespace.NamespaceContext;

/**
 * Dummy {@link NamespaceContext} implementation that contains no
 * namespace information, except bindings that are specified by
 * the namespace specification itself (for prefixes "xml" and "xmlns")
 */
public class EmptyNamespaceContext
    implements NamespaceContext
{
    final static EmptyNamespaceContext sInstance = new EmptyNamespaceContext();
    
    private EmptyNamespaceContext() { }

    public static EmptyNamespaceContext getInstance() { return sInstance; }

    /*
    /**********************************************************************
    /* NamespaceContext API
    /**********************************************************************
     */

    public final String getNamespaceURI(String prefix)
    {
        /* First the known offenders; invalid args, 2 predefined xml namespace
         * prefixes
         */
        if (prefix == null) {
            throw new IllegalArgumentException("Illegal to pass null/empty prefix as argument.");
        }
        if (prefix.length() > 0) {
            if (prefix.equals(XMLConstants.XML_NS_PREFIX)) {
                return XMLConstants.XML_NS_URI;
            }
            if (prefix.equals(XMLConstants.XMLNS_ATTRIBUTE)) {
                return XMLConstants.XMLNS_ATTRIBUTE_NS_URI;
            }
        }
        return null;
    }

    public String getPrefix(String nsURI)
    {
        /* First the known offenders; invalid args, 2 predefined xml namespace
         * prefixes
         */
        if (nsURI == null || nsURI.length() == 0) {
            throw new IllegalArgumentException("Illegal to pass null/empty URI as argument.");
        }
        if (nsURI.equals(XMLConstants.XML_NS_URI)) {
            return XMLConstants.XML_NS_PREFIX;
        }
        if (nsURI.equals(XMLConstants.XMLNS_ATTRIBUTE_NS_URI)) {
            return XMLConstants.XMLNS_ATTRIBUTE;
        }
        return null;
    }

    public Iterator getPrefixes(String nsURI)
    {
        /* First the known offenders; invalid args, 2 predefined xml namespace
         * prefixes
         */
        if (nsURI == null || nsURI.length() == 0) {
            throw new IllegalArgumentException("Illegal to pass null/empty prefix as argument.");
        }
        if (nsURI.equals(XMLConstants.XML_NS_URI)) {
            return SingletonIterator.create(XMLConstants.XML_NS_PREFIX);
        }
        if (nsURI.equals(XMLConstants.XMLNS_ATTRIBUTE_NS_URI)) {
            return SingletonIterator.create(XMLConstants.XMLNS_ATTRIBUTE);
        }
        return EmptyIterator.getInstance();
    }
}