java xml cast Node to Element

问题:

I know this was asked many times but I still cannot get it to work. I convert xml string to Document object and then parse it. Here is the code:

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.*;

DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder;
try
{
  builder = factory.newDocumentBuilder();  
  Document document = builder.parse( new InputSource( new StringReader( result ) ) );
  Node head = document.getFirstChild();
  if(head != null)
  {                  
    NodeList airportList = head.getChildNodes();      
    for(int i=0; i<airportList.getLength(); i++) {
    Node n = airportList.item(i);                        
    Element airportElem = (Element)n;
  }
}
catch (Exception e) {
  e.printStackTrace();
} 

When I cast the Node object n to Element I get an exception java.lang.ClassCastException: org.apache.harmony.xml.dom.TextImpl cannot be cast to org.w3c.dom.Element. When I check the node type of the Node object it says Node.TEXT_NODE. I believe it should be Node.ELEMENT_NODE. Am I right?

So how do I convert Node to Element, so I can do something like element.getAttribute("attrName").

Here is my XML:

<?xml version="1.0" encoding="utf-8" ?> 
<ArrayOfCity xmlns:xsd="http://www.w3.org/2001/XMLSchema"     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" >
<City>
  <strName>Abu Dhabi</strName> 
  <strCode>AUH</strCode> 
</City>
<City>
  <strName>Amsterdam</strName> 
  <strCode>AMS</strCode> 
</City>
<City>
  <strName>Antalya</strName> 
  <strCode>AYT</strCode> 
</City>
<City>
  <strName>Bangkok</strName> 
  <strCode>BKK</strCode> 
</City>
</ArrayOfCity>

Thanks in advance!

回答1:

When I cast the Node object n to Element I get an exception java.lang.ClassCastException: org.apache.harmony.xml.dom.TextImpl cannot be cast to org.w3c.dom.Element. When I check the node type of the Node object it says Node.TEXT_NODE. I believe it should be Node.ELEMENT_NODE. Am I right?

Probably not, the parser is probably right. It means that some of the nodes in what you're parsing are text nodes. For example:

<foo>bar</foo>

In the above, we have a foo element containing a text node. (The text node contains the text "bar".)

Similarly, consider:

<foo>
    <bar>baz</bar>
</foo>

If your XML document literally looks like the above, it contains a root element foo with these child nodes (in order):

• A text node with some whitespace in it
• A bar element
• A text node with some more whitespace in it

Note that the bar element is not the first child of foo. If it looked like this:

<foo><bar>baz</bar></foo>

then the bar element would be the first child of foo.

回答2:

I think you need something like this:

NodeList airportList = head.getChildNodes();
for (int i = 0; i < airportList.getLength(); i++) {
    Node n = airportList.item(i);
    if (n.getNodeType() == Node.ELEMENT_NODE) {
        Element elem = (Element) n;
    }
}

回答3:

you can also try to "protect" your casting

Node n = airportList.item(i);
if (n instanceof Element)
{                        
    Element airportElem = (Element)n;
    // ...
}

but as pointed by others, you have text node, those won't be casted by this method, be sure you don't need them of use the condition to have a different code to process them