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9.2

Java XPath evaluate() problem

Asked by UTEK in XPath, Extensible Markup Language (XML), Java Standard Edition

Tags: Java, XML, Xpath, evaluate

I have this sample code. I would expect the output to be something like

Channel #0
Channel Name : Ch1
Channel #1
Channel Name : Ch2
Channel #2
Channel Name : Ch3

but all I get is

Channel #0
Channel Name : Ch1
Channel #1
Channel Name : Ch1
Channel #2
Channel Name : Ch1

Do I misuse the evaluate() method? It seems the evaluate method disregards the"doc" start node I pass in and always start from the beginning of the XML...
Very appreciate your suggestion. Thank you very much.
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import javax.xml.xpath.*;
import org.xml.sax.InputSource;
import java.io.StringReader;
import org.w3c.dom.Document;
import org.w3c.dom.NodeList;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
 
public class EvaluateTest {
 
   /**
    * @param args
    */
   public static void main(String[] args) {
      String myxml = "<?xml version='1.0' encoding='utf-8' ?><mytest><ChannelList>" + 
	             "<Channel><ChannelId>0001</ChannelId><ChannelName>Ch1</ChannelName></Channel>" +
                             "<Channel><ChannelId>0002</ChannelId><ChannelName>Ch2</ChannelName></Channel>" +
	             "<Channel><ChannelId>0003</ChannelId><ChannelName>Ch3</ChannelName></Channel>" +
	             "</ChannelList></mytest>";
			
      //Get the Document object
      Document doc = null;
      try {
            InputSource inputSource = new InputSource();
            inputSource.setCharacterStream( new StringReader(myxml));
            DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
            DocumentBuilder db = factory.newDocumentBuilder();
            doc = db.parse(inputSource);
					
            //Iterate thru the Channel list 
            NodeList channellist = getSubElements(doc, "/mytest/ChannelList/Channel");
            if (channellist==null)
                  System.out.println("the channel list is null");
		
            for (int i=0, len=channellist.getLength(); i<len; i++) {
                  System.out.println("Channel #" + i);
				
                  String name = getTagValue(channellist.item(i), "//ChannelName/text()", -1);
                  System.out.println("Channel Name : " + name);
            }
      } catch ( Exception e ) {
            e.printStackTrace();
            return;
      }
   }
	
	
   //Get the text value of a tag from a document object using XPath method
   static public String getTagValue(Object doc, String xpathstr, int index) throws Exception {
      String result = "";
		
      if ((doc==null)	|| (xpathstr==null) || "".equals(xpathstr)) 
            return result;
		
      XPathFactory factory = XPathFactory.newInstance();
      XPath xpath = factory.newXPath();
      result = (String)xpath.evaluate(xpathstr, doc, XPathConstants.STRING);
      if (result==null)
            result = "";
		
      return result;
   }
	
	
   static public NodeList getSubElements(Object doc, String xpathstr) throws Exception {
      if ((doc==null)	|| (xpathstr==null) || "".equals(xpathstr)) 
            return null;
		
      XPathFactory factory = XPathFactory.newInstance();
      XPath xpath = factory.newXPath();
      Object result = xpath.evaluate(xpathstr, doc, XPathConstants.NODESET);
      return (NodeList)result;
   }
 
}
[+][-]06/08/09 08:27 AM, ID: 24573092Accepted Solution

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About this solution

Zones: XPath, Extensible Markup Language (XML), Java Standard Edition
Tags: Java, XML, Xpath, evaluate
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Solution Provided By: TomLun
Participating Experts: 1
Solution Grade: A
 
[+][-]06/08/09 08:57 AM, ID: 24573459Author Comment

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[+][-]06/08/09 09:01 AM, ID: 24573503Expert Comment

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