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Extension for Jackson (http://jackson.codehaus.org) to offer alternative support for serializing POJOs as XML and deserializing XML as pojos. Support implemented on top of Stax API (javax.xml.stream), by implementing core Jackson Streaming API types like JsonGenerator, JsonParser and JsonFactory. Some data-binding types overridden as well (ObjectMapper sub-classed as XmlMapper).

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package com.fasterxml.jackson.xml;

import javax.xml.namespace.QName;

import org.codehaus.jackson.map.AnnotationIntrospector;
import org.codehaus.jackson.map.introspect.Annotated;

/**
 * Additional extension interface used above and beyond
 * {@link AnnotationIntrospector} to
 * handle XML-specific configuration.
 * 
 * @since 1.7
 */
public interface XmlAnnotationIntrospector
{
    /**
     * Method that can be called to figure out generic namespace
     * property for an annotated object.
     *
     * @return Null if annotated thing does not define any
     *   namespace information; non-null namespace (which may
     *   be empty String) otherwise
     */
    public String findNamespace(Annotated ann);

    /**
     * Method used to check whether given annotated element
     * (field, method, constructor parameter) has indicator that suggest
     * it be output as an XML attribute or not (as element)
     */
    public Boolean isOutputAsAttribute(Annotated ann);

    /**
     * Method used to check if specified property has annotation that indicates
     * that it should be wrapped in an element; and if so, name to use.
     * Note: local name of "" is used to indicate that name should default
     * to using name (local name and namespace) of property itself.
     */
    public QName findWrapperElement(Annotated ann);

    /**
     * Method used to find out name to use for the outermost (root) XML element
     * name when serializing (since there is no property that would define it);
     * this overrides default name based on type of object.
     */
    public QName findRootElement(Annotated ann);
    
    /*
    /**********************************************************************
    /* Replacement of 'AnnotationIntrospector.Pair' to use when combining
    /* (potential) XMLAnnotationIntrospector instance
    /**********************************************************************
     */

    /**
     * Extension of AnnotationIntrospector.Pair that can
     * also dispatch 'XmlAnnotationIntrospector' methods.
     */
    public static class Pair extends AnnotationIntrospector.Pair
        implements XmlAnnotationIntrospector
    {
        protected final XmlAnnotationIntrospector _xmlPrimary;
        protected final XmlAnnotationIntrospector _xmlSecondary;
        
        public Pair(AnnotationIntrospector p, AnnotationIntrospector s)
        {
            super(p, s);
            _xmlPrimary = (p instanceof XmlAnnotationIntrospector) ? (XmlAnnotationIntrospector) p : null;
            _xmlSecondary = (s instanceof XmlAnnotationIntrospector) ? (XmlAnnotationIntrospector) s : null;
        }

        public static XmlAnnotationIntrospector.Pair instance(AnnotationIntrospector a1, AnnotationIntrospector a2) {
            return new XmlAnnotationIntrospector.Pair(a1, a2);
        }
        
        @Override
        public String findNamespace(Annotated ann)
        {
            String value = (_xmlPrimary == null) ? null : _xmlPrimary.findNamespace(ann);
            if (value == null && _xmlSecondary != null) {
                value = _xmlSecondary.findNamespace(ann);
            }
            return value;
        }

        @Override
        public QName findWrapperElement(Annotated ann)
        {
            QName value = (_xmlPrimary == null) ? null : _xmlPrimary.findWrapperElement(ann);
            if (value == null && _xmlSecondary != null) {
                value = _xmlSecondary.findWrapperElement(ann);
            }
            return value;
        }

        @Override
        public QName findRootElement(Annotated ann)
        {
            QName value = (_xmlPrimary == null) ? null : _xmlPrimary.findRootElement(ann);
            if (value == null && _xmlSecondary != null) {
                value = _xmlSecondary.findRootElement(ann);
            }
            return value;
        }
        
        @Override
        public Boolean isOutputAsAttribute(Annotated ann)
        {
            Boolean value = (_xmlPrimary == null) ? null : _xmlPrimary.isOutputAsAttribute(ann);
            if (value == null && _xmlSecondary != null) {
                value = _xmlSecondary.isOutputAsAttribute(ann);
            }
            return value;
        }
    }
}