JDOM, XPath and Namespace Interactions

问题

I'm having a very frustrating time extracting some elements from a JDOM document using an XPath expression. Here's a sample XML document - I'd like to remove the ItemCost elements from the document altogether, but I'm having trouble getting an XPath expression to evaluate to anything at the moment.

  <srv:getPricebookByCompanyResponse xmlns:srv="http://ess.com/ws/srv">
     <srv:Pricebook>
        <srv:PricebookName>Demo Operator Pricebook</srv:PricebookName>
        <srv:PricebookItems>
           <srv:PricebookItem>
              <srv:ItemName>Demo Wifi</srv:ItemName>
              <srv:ProductCode>DemoWifi</srv:ProductCode>
              <srv:ItemPrice>15</srv:ItemPrice>
              <srv:ItemCost>10</srv:ItemCost>
           </srv:PricebookItem>
           <srv:PricebookItem>
              <srv:ItemName>1Mb DIA</srv:ItemName>
              <srv:ProductCode>Demo1MbDIA</srv:ProductCode>
              <srv:ItemPrice>20</srv:ItemPrice>
              <srv:ItemCost>15</srv:ItemCost>
           </srv:PricebookItem>
        </srv:PricebookItems>
     </srv:Pricebook>
  </srv:getPricebookByCompanyResponse>

I would normally just use an expression such as //srv:ItemCost to identify these elements, which works fine on other documents, however here it continually returns 0 nodes in the List. Here's the code I've been using:

Namespace ns = Namespace.getNamespace("srv","http://ess.com/ws/srv");   
XPath filterXpression = XPath.newInstance("//ItemCost");
filterXpression.addNamespace(ns);   
List nodes = filterXpression.selectNodes(response);

Where response is a JDOM element containing the above XML snippet (verified with an XMLOutputter). nodes continually has size()==0 whenever parsing this document. Using the XPath parser in Eclipse on the same document, this expression does not work either. After some digging, I got the Eclipse evaluator to work with the following expression: //*[local-name() = 'ItemCost'], however replacing the //srv:ItemCost in the Java code with this still produced no results. Another thing I noticed is if I remove the namespace declaration from the XML, //srv:ItemCost will resolve correctly in the Eclipse parser, but I can't remove it from the XML. I've been scratching my head for ours hours on this one now, and would really appreciate some nudging in the right direction.

Many thanks

Edit : Fixed code -

Document build = new Document(response);
XPath filterXpression = XPath.newInstance("//srv:ItemCost");
List nodes = filterXpression.selectNodes(build);

回答1:

Strange, indeed... I tested on my side with jdom, and your snippet produced an empty list, the following works as intended:

public static void main(String[] args) throws JDOMException, IOException {
    File xmlFile = new File("sample.xml");
    SAXBuilder builder = new SAXBuilder();
    Document build = builder.build(xmlFile);        
    XPath filterXpression = XPath.newInstance("//srv:ItemCost");
    System.out.println(filterXpression.getXPath());
    List nodes = filterXpression.selectNodes(build);        
    System.out.println(nodes.size());
}

It produces the output:

//srv:ItemCost
2

来源：https://stackoverflow.com/questions/3181055/jdom-xpath-and-namespace-interactions

标签

java

xpath

namespaces

jdom