modules/databinding-jaxb/src/main/java/org/apache/tuscany/sca/databinding/jaxb/XMLRootElementUtil.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied. See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.tuscany.sca.databinding.jaxb;

import java.beans.IntrospectionException;
import java.beans.Introspector;
import java.beans.PropertyDescriptor;
import java.lang.annotation.Annotation;
import java.lang.reflect.AnnotatedElement;
import java.lang.reflect.Field;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.StringTokenizer;
import java.util.WeakHashMap;

import javax.xml.bind.JAXBElement;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlElementRef;
import javax.xml.bind.annotation.XmlEnumValue;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlSchema;
import javax.xml.namespace.QName;

/**
 * 
 */
public class XMLRootElementUtil {

    /**
     * TUSCANY-3167
     * Cache for property descriptors
     */
    private static Map<Class<?>, Map<String, JAXBPropertyDescriptor>> PROPERTY_MAP =
        new WeakHashMap<Class<?>, Map<String, JAXBPropertyDescriptor>>();

    /** Constructor is intentionally private.  This class only provides static utility methods */
    private XMLRootElementUtil() {

    }

    /**
     * @param clazz
     * @return namespace of root element qname or null if this is not object does not represent a
     *         root element
     */
    public static QName getXmlRootElementQNameFromObject(Object obj) {

        // A JAXBElement stores its name
        if (obj instanceof JAXBElement) {
            return ((JAXBElement<?>)obj).getName();
        }

        Class<?> clazz = (obj instanceof java.lang.Class) ? (Class<?>)obj : obj.getClass();
        return getXmlRootElementQName(clazz);
    }

    /**
     * @param clazz
     * @return namespace of root element qname or null if this is not object does not represent a
     *         root element
     */
    public static QName getXmlRootElementQName(Class<?> clazz) {

        // See if the object represents a root element
        XmlRootElement root = (XmlRootElement)getAnnotation(clazz, XmlRootElement.class);
        if (root == null) {
            return null;
        }

        String name = root.name();
        String namespace = root.namespace();

        // The name may need to be defaulted
        if (name == null || name.length() == 0 || name.equals("##default")) {
            name = getSimpleName(clazz.getCanonicalName());
        }

        // The namespace may need to be defaulted
        if (namespace == null || namespace.length() == 0 || namespace.equals("##default")) {
            Package pkg = clazz.getPackage();
            XmlSchema schema = (XmlSchema)getAnnotation(pkg, XmlSchema.class);
            if (schema != null) {
                namespace = schema.namespace();
            } else {
                namespace = "";
            }
        }

        return new QName(namespace, name);
    }

    /**
     * @param clazz
     * @return namespace of root element qname or null if this is not object does not represent a root element
     */
    public static String getEnumValue(Enum<?> myEnum) {
        Field f;
        String value;
        try {
            f = myEnum.getClass().getField(myEnum.name());

            f.setAccessible(true);

            XmlEnumValue xev = (XmlEnumValue)getAnnotation(f, XmlEnumValue.class);
            if (xev == null) {
                value = f.getName();
            } else {
                value = xev.value();
            }
        } catch (SecurityException e) {
            value = null;
        } catch (NoSuchFieldException e) {
            value = null;
        }

        return value;
    }

    /**
     * utility method to get the last token in a "."-delimited package+classname string
     *
     * @return
     */
    private static String getSimpleName(String in) {
        if (in == null || in.length() == 0) {
            return in;
        }
        String out = null;
        StringTokenizer tokenizer = new StringTokenizer(in, ".");
        if (tokenizer.countTokens() == 0)
            out = in;
        else {
            while (tokenizer.hasMoreTokens()) {
                out = tokenizer.nextToken();
            }
        }
        return out;
    }

    /**
     * The JAXBClass has a set of bean properties each represented by a PropertyDescriptor Each of
     * the fields of the class has an associated xml name. The method returns a map where the key is
     * the xml name and value is the PropertyDescriptor
     *
     * @param jaxbClass
     * @return map
     */
    public synchronized static Map<String, JAXBPropertyDescriptor> createPropertyDescriptorMap(Class<?> jaxbClass)
        throws NoSuchFieldException, IntrospectionException {

        Map<String, JAXBPropertyDescriptor> map = PROPERTY_MAP.get(jaxbClass);
        if (map != null) {
            return map;
        }

        map = new HashMap<String, JAXBPropertyDescriptor>();
        PropertyDescriptor[] pds = Introspector.getBeanInfo(jaxbClass).getPropertyDescriptors();

        // Unfortunately the element names are stored on the fields.
        // Get all of the fields in the class and super classes

        List<Field> fields = getFields(jaxbClass);

        // Now match up the fields with the property descriptors...Sigh why didn't JAXB put the @XMLElement annotations on the 
        // property methods!
        for (PropertyDescriptor pd : pds) {

            // Skip over the class property..it is never represented as an xml element
            if (pd.getName().equals("class")) {
                continue;
            }

            // For the current property, find a matching field...so that we can get the xml name
            boolean found = false;

            int index = 0;
            for (Field field : fields) {
                String fieldName = field.getName();

                // Use the name of the field and property to find the match
                if (fieldName.equalsIgnoreCase(pd.getDisplayName()) || fieldName.equalsIgnoreCase(pd.getName())) {
                    // Get the xmlElement name for this field
                    QName xmlName = getXmlElementRefOrElementQName(field.getDeclaringClass(), field);
                    found = true;
                    map.put(xmlName.getLocalPart(), new JAXBPropertyDescriptor(pd, xmlName, index));
                    index++;
                    break;
                }

                // Unfortunately, sometimes the field name is preceeded by an underscore
                if (fieldName.startsWith("_")) {
                    fieldName = fieldName.substring(1);
                    if (fieldName.equalsIgnoreCase(pd.getDisplayName()) || fieldName.equalsIgnoreCase(pd.getName())) {
                        // Get the xmlElement name for this field
                        QName xmlName = getXmlElementRefOrElementQName(field.getDeclaringClass(), field);
                        found = true;

                        map.put(xmlName.getLocalPart(), new JAXBPropertyDescriptor(pd, xmlName, index));
                        index++;
                        break;
                    }
                }
            }

            // We didn't find a field.  Default the xmlname to the property name
            if (!found) {
                String xmlName = pd.getName();

                map.put(xmlName, new JAXBPropertyDescriptor(pd, xmlName, index));
                index++;
            }
        }
        PROPERTY_MAP.put(jaxbClass, map);
        return map;
    }

    /**
     * Gets all of the fields in this class and the super classes
     *
     * @param beanClass
     * @return
     */
    static private List<Field> getFields(final Class<?> beanClass) {
        // This class must remain private due to Java 2 Security concerns
        List<Field> fields = AccessController.doPrivileged(new PrivilegedAction<List<Field>>() {
            public List<Field> run() {
                List<Field> fields = new ArrayList<Field>();
                Class<?> cls = beanClass;
                while (cls != null) {
                    Field[] fieldArray = cls.getDeclaredFields();
                    for (Field field : fieldArray) {
                        fields.add(field);
                    }
                    cls = cls.getSuperclass();
                }
                return fields;
            }
        });

        return fields;
    }

    /**
     * Get the name of the field by looking at the XmlElement annotation.
     *
     * @param jaxbClass
     * @param fieldName
     * @return
     * @throws NoSuchFieldException
     */
    private static QName getXmlElementRefOrElementQName(Class<?> jaxbClass, Field field) throws NoSuchFieldException {
        XmlElementRef xmlElementRef = (XmlElementRef)getAnnotation(field, XmlElementRef.class);
        if (xmlElementRef != null) {
            return new QName(xmlElementRef.namespace(), xmlElementRef.name());
        }
        XmlElement xmlElement = (XmlElement)getAnnotation(field, XmlElement.class);

        // If XmlElement does not exist, default to using the field name
        if (xmlElement == null || xmlElement.name().equals("##default")) {
            return new QName("", field.getName());
        }
        return new QName(xmlElement.namespace(), xmlElement.name());
    }

    /**
     * Get an annotation.  This is wrappered to avoid a Java2Security violation.
     * @param cls Class that contains annotation 
     * @param annotation Class of requrested Annotation
     * @return annotation or null
     */
    private static <T extends Annotation> T getAnnotation(final AnnotatedElement element, final Class<T> annotation) {
        return AccessController.doPrivileged(new PrivilegedAction<T>() {
            public T run() {
                return element.getAnnotation(annotation);
            }
        });
    }
}