RDFUtil.java

/**
 * Copyright 2008 The University of North Carolina at Chapel Hill
 *
 * Licensed 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 edu.unc.lib.dl.util;

import java.util.List;

import org.jdom2.Element;

import edu.unc.lib.dl.xml.JDOMNamespaceUtil;

public class RDFUtil {

	/**
	 * Adds all elements from an incoming RDF element into a base RDF element without overwriting any existing data
	 * 
	 * @param baseRDF
	 * @param incomingRDF
	 * @return
	 */
	public static Element mergeRDF(Element baseRDF, Element incomingRDF) {
		if (baseRDF == null)
			return incomingRDF;
		if (incomingRDF == null)
			return baseRDF;
		List<?> incomingChildren = incomingRDF.getChildren("Description", JDOMNamespaceUtil.RDF_NS);
		// If there is no rdf:Description tag in the incoming data, then there is nothing to add.
		if (incomingChildren.size() == 0)
			return baseRDF;

		Element incomingDescription = (Element) incomingChildren.get(0);
		Element newDescription = null;

		newDescription = baseRDF.getChild("Description", JDOMNamespaceUtil.RDF_NS);
		// If the previous rels-ext didn't have a description, then use the new one
		if (newDescription == null) {
			baseRDF.addContent((Element) incomingDescription.clone());
			return baseRDF;
		}

		// Clone all the child elements of the incoming rdf:Description tag
		List<?> incomingElements = incomingDescription.getChildren();
		// Add all the incoming element children to the base modified object
		for (Object incomingObject : incomingElements) {
			if (incomingObject instanceof Element)
				newDescription.addContent((Element) ((Element) incomingObject).clone());
		}

		return baseRDF;
	}

	/**
	 * Adds all elements from an incoming RDF element into a base RDF element, where all relations in the incoming element
	 * will overwrite those in the base element when they match on both subject and predicate.
	 * 
	 * @param baseRDF
	 * @param incomingRDF
	 * @return
	 */
	public static Element updateRDF(Element baseRDF, Element incomingRDF) {
		if (baseRDF == null)
			return incomingRDF;
		if (incomingRDF == null)
			return baseRDF;
		// If there is no rdf:Description tag in the incoming data, then there is nothing to add.
		if (incomingRDF.getChildren().size() == 0)
			return baseRDF;

		Element incomingDescription = (Element) incomingRDF.getChildren("Description", JDOMNamespaceUtil.RDF_NS).get(0);
		Element newDescription = null;

		// If the previous rels-ext didn't have a description, then use the new one
		if (baseRDF.getChildren().size() == 0) {
			baseRDF.addContent((Element) incomingDescription.clone());
			return baseRDF;
		} else {
			newDescription = (Element) baseRDF.getChildren().get(0);
		}

		// Clone all the child elements of the incoming rdf:Description tag
		List<Element> incomingElements = (List<Element>) incomingDescription.getChildren();
		// Add all the incoming element children to the base modified object
		for (Element incomingElement : incomingElements) {
			// Remove the preexisting relations of the same type before adding the new entries
			newDescription.removeChildren(incomingElement.getName(), incomingElement.getNamespace());
			newDescription.addContent((Element) incomingElement.clone());
		}

		return baseRDF;
	}
}