Confusion with parsing XML file in Java

Given this XML file:

<?xml version="1.0" encoding="UTF-8"?>
<root>
   <data>
      <track clipid="1">
         <url>http://www.emp3world.com/to_download.php?id=33254</url>
         <http_method>GET or POST</http_method>
         <post_body>a=1&b=2&c=3</post_body>
      </track>
   </data>
</root>

What I am after is to print something like this from this XML file:

ID: 1
URL: http://www.emp3world.com/to_download.php?id=33254
Http method: GET or POST

At the moment this is my primitive handler code:

class MyHandler extends DefaultHandler
{
    String str = "";
    StringBuilder s = new StringBuilder();
    public void startElement(String namespaceURI, String sName, String qName, Attributes atts)
    {
        if(qName.equals("track"))
        {
            s.append("ID: ").append(atts.getValue("clipid")).append("n");
        }
        if(qName.equals("url"))
        {
            s.append("URL: ");
        }
        if(qName.equals("http_method"))
        {
            s.append("Http method: ");
        }
    }

    public void endElement(String uri, String localName, String qName)
    {
        if(qName.equals("url"))
        {
            s.append(str).append("n");
            str = "";
        }
        if(qName.equals("http_method"))
        {
            s.append(str).append("n");
            str = "";
        }
        System.out.println(s);
    }

    public void characters(char[] ch, int start, int length) throws SAXException {
        str = new String(ch, start, length);
    }
}

My problem is that it always prints the results 4 times(first time without the Http Method field. I guess this is a problem for all Sax Parsers beginners.
I know what startElement, endElement, characters functions do, but as you can see, I don’t know how to use them correctly. What should I change in my code so I can have the correct output?

Answer

The problem is your characters method. Change its body to

s.append(new String(ch, start, length));

then add this line to the start of startElement

s.setLength(0);

and you should see some output.

Here’s what the Java tutorial on SAX has to say about the characters method:

Parsers are not required to return any particular number of characters at one time. A parser can return anything from a single character at a time up to several thousand and still be a standard-conforming implementation. So if your application needs to process the characters it sees, it is wise to have the characters() method accumulate the characters in a java.lang.StringBuffer and operate on them only when you are sure that all of them have been found.

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