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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.jaxb;

import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlElementWrapper;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.namespace.QName;

import org.codehaus.jackson.map.introspect.Annotated;
import org.codehaus.jackson.map.introspect.AnnotatedClass;
import org.codehaus.jackson.xc.JaxbAnnotationIntrospector;

import com.fasterxml.jackson.xml.XmlAnnotationIntrospector;

/**
 * Alternative {@link org.codehaus.jackson.map.AnnotationIntrospector} implementation that
 * builds on introspector from Jackson XC package that uses JAXB annotations,
 * not Jackson annotations.
 */
public class XmlJaxbAnnotationIntrospector
    extends JaxbAnnotationIntrospector
    implements XmlAnnotationIntrospector
{
    @Override
    public String findNamespace(Annotated ann)
    {
        String ns = null;

        /* 10-Oct-2009, tatus: I suspect following won't work quite
         *  as well as it should, wrt. defaulting to package.
         *  But it should work well enough to get things started --
         *  currently this method is not needed, and when it is,
         *  this can be improved.
         */

        if (ann instanceof AnnotatedClass) {
            /* For classes, it must be @XmlRootElement. Also, we do
             * want to use defaults from package, base class
             */
            XmlRootElement elem = findRootElementAnnotation((AnnotatedClass) ann);
            if (elem != null) {
                ns = elem.namespace();
            }
        } else {
            // For others, XmlElement or XmlAttribute work (anything else?)
            XmlElement elem = findAnnotation(XmlElement.class, ann, false, false, false);
            if (elem != null) {
                ns = elem.namespace();
            }
            if (ns == null || MARKER_FOR_DEFAULT.equals(ns)) {
                XmlAttribute attr = findAnnotation(XmlAttribute.class, ann, false, false, false);
                if (attr != null) {
                    ns = attr.namespace();
                }
            }
        }
        // JAXB uses marker for "not defined"
        if (MARKER_FOR_DEFAULT.equals(ns)) {
            ns = null;
        }
        return ns;
    }

    /**
     * Here we assume fairly simple logic; if there is XmlAttribute to be found,
     * we consider it an attibute; if XmlElement, not-an-attribute; and otherwise
     * we will consider there to be no information.
     * Caller is likely to default to considering things as elements.
     */
    @Override
    public Boolean isOutputAsAttribute(Annotated ann)
    {
        XmlAttribute attr = findAnnotation(XmlAttribute.class, ann, false, false, false);
        if (attr != null) {
            return Boolean.TRUE;
        }
        XmlElement elem = findAnnotation(XmlElement.class, ann, false, false, false);
        if (elem != null) {
            return Boolean.FALSE;
        }
        return null;
    }

    @Override
    public QName findWrapperElement(Annotated ann)
    {
        XmlElementWrapper w = findAnnotation(XmlElementWrapper.class, ann, false, false, false);
        if (w != null) {
            return new QName(handleJaxbDefault(w.namespace()), handleJaxbDefault(w.name()));
        }
        return null;
    }

    @Override
    public QName findRootElement(Annotated ann)
    {
        XmlRootElement root = findAnnotation(XmlRootElement.class, ann, false, false, false);
        if (root != null) {
            return new QName(handleJaxbDefault(root.namespace()), handleJaxbDefault(root.name()));
        }
        return null;
    }
    
    /*
    /**********************************************************************
    /* Helper methods
    /**********************************************************************
     */
    
    private XmlRootElement findRootElementAnnotation(AnnotatedClass ac)
    {
        // Yes, check package, no class (already included), yes superclasses
        return findAnnotation(XmlRootElement.class, ac, true, false, true);
    }

    private String handleJaxbDefault(String value)
    {
        return MARKER_FOR_DEFAULT.equals(value) ? "" : value;
    }

}