使用Xpath读取节点列表

Question

this is my XML file :

<sitemesh>
    <mapping path="/editor/tempPage/**" exclude="true"/>

        <mapping decorator="/WEB-INF/views/decorators/detailstheme.jsp"
            path="/*" exclude="false" />

    </sitemesh>

I want list of mapping node with their attribute values. this should be done using Xpath.

my xpath expression is :

expr = xpath.compile("/sitemesh/mapping");

but i am getting null in nodelist.

this is my code:

Map<String,String> map=new HashMap<String, String>();

        // reading xml file
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder;
        Document doc = null;
        XPathExpression expr = null;
        try {
            builder = factory.newDocumentBuilder();
            // creating input stream
            doc = builder.parse(file);
            XPathFactory xpf = XPathFactory.newInstance();
            XPath xpath = xpf.newXPath();
            expr = xpath.compile("//mapping");
        } catch (Exception e) {
            LOG.error("some exception message", e);
        }


        //------------------------------------------------------------------------

        NodeList attributeElements = null;
        try {
            attributeElements =(NodeList)expr.evaluate(doc, XPathConstants.NODE);

        } catch (XPathExpressionException e) {
            LOG.error("some exception message", e);
        }
        System.out.println("lenght:"+attributeElements.getLength());
        for (int i = 0; i < attributeElements.getLength(); i++) {
                Node node=attributeElements.item(i);
                System.out.println("node:"+node.getNodeValue());
             NamedNodeMap attrs = node.getAttributes();  
              for(i = 0 ; i<attrs.getLength() ; i++) {
                Attr attribute = (Attr)attrs.item(i);  
                System.out.println("Node Attributes : " + attribute.getName()+" = "+attribute.getValue());
              }
        }


        //-------------------------------------------------------------------------

        // writing xml file
        TransformerFactory transformerFactory = TransformerFactory
                .newInstance();
        Transformer transformer;
        try {
            transformer = transformerFactory.newTransformer();
            DOMSource source = new DOMSource(doc);
            StreamResult result = new StreamResult(file);// creating output
                                                            // stream
            transformer.transform(source, result);
        } catch (Exception e) {
            LOG.error("some exception message", e);
        }

        return   map;

i am getting null for attributeElements

i want to show values of path,decorator and exclude on JSP page.But i am unable to get list of node through xpath expression.

I want solution for reading mapping node element in Xpath.

Answer 1

[edit] /sitemesh/mapping also works .

The issue here is that you evaluating the express for XPathConstants.NODE while the nodeList maps to XPathConstants.NODESET . please refer below link.

http://docs.oracle.com/javase/1.5.0/docs/api/javax/xml/xpath/XPathConstants.html#NODESET

Added sample code for illustration purpose only:

public void testXpathExpr(){

String testXML = "<sitemesh><mapping path=\"/editor/tempPage/**\" exclude=\"true\"/><mapping decorator=\"/WEB-INF/views/decorators/detailstheme.jsp\" path=\"/*\" exclude=\"false\" /></sitemesh>";

NodeList nodeList = getNodeList(testXML);
}

private NodeList getNodeList(String xml) throws SAXException, IOException, ParserConfigurationException, XPathExpressionException {
  DocumentBuilderFactory docFactory = DocumentBuilderFactory.newInstance();
  DocumentBuilder builder = docFactory.newDocumentBuilder();

  document = builder.parse(new ByteArrayInputStream( xml.getBytes() ) );
  XPathExpression exprPath = xpath.compile(xpathExpr);
  NodeList nodeList = (NodeList) exprPath.evaluate(document, XPathConstants.NODESET);;
return nodeList;
}

Hope this helps!

Answer 2

Your xpath works perfectly for me. Below is the sample code:

public class Parser {

    public static void main(String[] args) throws Exception, Exception {
        final DocumentBuilderFactory factory = DocumentBuilderFactory
                .newInstance();
        final DocumentBuilder builder = factory.newDocumentBuilder();
        final Document doc = builder.parse("src/sitemesh.xml");
        final XPathFactory xPathfactory = XPathFactory.newInstance();
        final XPath xpath = xPathfactory.newXPath();
        final XPathExpression expr = xpath.compile("/sitemesh/mapping");
        Object node = expr.evaluate(doc, XPathConstants.NODE);

        System.out.println(node);
    }
}

sitemesh.xml contains your sample input.