ElementIdGenerator.java

/*
 *    Copyright (c) 2013, University of Toronto.
 * 
 *    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.toronto.cs.xcurator.common;

import edu.toronto.cs.xcurator.common.NsContext;
import edu.toronto.cs.xcurator.common.XPathFinder;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.xml.xpath.XPathExpressionException;
import org.apache.xml.serialize.OutputFormat;
import org.apache.xml.serialize.XMLSerializer;
import org.w3c.dom.Document;
import org.w3c.dom.Element;

public class ElementIdGenerator {

    private final String resourceUriPattern;

    public ElementIdGenerator(String resourceUriBase) {
        this.resourceUriPattern = (resourceUriBase.endsWith("/") ? resourceUriBase
                : resourceUriBase + "/") + "${UUID}";
    }

    public String generateUri(NsContext entityNamespaceContext,
            Element element, Document dataDoc, XPathFinder xpath)
            throws NoSuchAlgorithmException, IOException, XPathExpressionException {
        return generateUri(this.resourceUriPattern, entityNamespaceContext, element, dataDoc, xpath);
    }

    public String generateUri(String resourceUriPattern, NsContext entityNamespaceContext,
            Element element, Document dataDoc, XPathFinder xpath)
            throws NoSuchAlgorithmException, IOException, XPathExpressionException {
        int lastEndIndex = 0;
        String id = resourceUriPattern != null ? resourceUriPattern : this.resourceUriPattern;
        String uuidPattern = "UUID";
        String generatedId = "";
        do {
            int startIndex = id.indexOf("${", lastEndIndex);
            if (startIndex == -1) {
                break;
            }
            int endIndex = id.indexOf("}", startIndex);
            if (endIndex == -1) {
                break;
            }
            String literal = id.substring(lastEndIndex, startIndex);
            String path = id.substring(startIndex + 2, endIndex);
            String pathValue = null;
            if (uuidPattern.equals(path)) {
                MessageDigest digest = MessageDigest.getInstance("MD5");
                pathValue = "";
                byte[] md5 = digest.digest(asByteArray(element));
                for (byte b : md5) {
                    pathValue += Integer.toString((b & 0xff) + 0x100, 16).substring(1);
                }
            } else {
                pathValue = xpath.getStringByPath(path, element, dataDoc, entityNamespaceContext);
            }
            generatedId += literal + pathValue;
            lastEndIndex = endIndex + 1;
        } while (true);

        if (generatedId.trim().length() == 0) {
            String messString = "Error in generating id: " + element.toString();
            Logger.getLogger(ElementIdGenerator.class.getName()).log(Level.SEVERE, messString);
        }
        return generatedId;
    }

    public byte[] asByteArray(Element element) throws IOException {
        ByteArrayOutputStream bis = new ByteArrayOutputStream();

        OutputFormat format = new OutputFormat(element.getOwnerDocument());
        XMLSerializer serializer = new XMLSerializer(
                bis, format);
        serializer.asDOMSerializer();
        serializer.serialize(element);

        return bis.toByteArray();
    }
}