Starting from a node, find the namespace declaration for a prefix. : Namespace « XML « Java Tutorial

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/**
 * 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.
 */

import java.util.List;

import javax.xml.XMLConstants;

import org.w3c.dom.Element;
import org.w3c.dom.NamedNodeMap;
import org.w3c.dom.Node;
/**
 * Few simple utils to read DOM. This is originally from the Jakarta Commons Modeler.
 * 
 * @author Costin Manolache
 */
public class Utils {
  private static final String XMLNAMESPACE = "xmlns";
  /**
   * Starting from a node, find the namespace declaration for a prefix. for a matching namespace
   * declaration.
   * 
   * @param node search up from here to search for namespace definitions
   * @param searchPrefix the prefix we are searching for
   * @return the namespace if found.
   */
  public static String getNamespace(Node node, String searchPrefix) {

      Element el;
      while (!(node instanceof Element)) {
          node = node.getParentNode();
      }
      el = (Element)node;

      NamedNodeMap atts = el.getAttributes();
      for (int i = 0; i < atts.getLength(); i++) {
          Node currentAttribute = atts.item(i);
          String currentLocalName = currentAttribute.getLocalName();
          String currentPrefix = currentAttribute.getPrefix();
          if (searchPrefix.equals(currentLocalName) && XMLNAMESPACE.equals(currentPrefix)) {
              return currentAttribute.getNodeValue();
          } else if (isEmpty(searchPrefix) && XMLNAMESPACE.equals(currentLocalName)
                     && isEmpty(currentPrefix)) {
              return currentAttribute.getNodeValue();
          }
      }

      Node parent = el.getParentNode();
      if (parent instanceof Element) {
          return getNamespace((Element)parent, searchPrefix);
      }

      return null;
  }
  public static boolean isEmpty(String str) {
    return str == null || str.length() == 0;
}
}