Xalan: The org.apache.xpath.CachedXPathAPI Class

Extends: java.lang.Object

Members

Overview

This is an alternative for the old XPathAPI class, which provided static methods for the purpose but had the drawback of instantiating a new XPathContext (and thus building a new DTMManager, and new DTMs) each time it was called. XPathAPIObject instead retains its context as long as the object persists, reusing the DTMs. This does have a downside: if you've changed your source document, you should obtain a new XPathAPIObject to continue searching it, since trying to use the old DTMs will probably yield bad results or malfunction outright... and the cached DTMs may consume memory until this object and its context are returned to the heap. Essentially, it's the caller's responsibility to decide when to discard the cache.

Method Overviews

The methods in this class are convenience methods into the low-level XPath API. These functions tend to be a little slow, since a number of objects must be created for each evaluation.

When performance is a issue, then better to use precompile the XPaths using the low-level API, and then just use the XPaths over and over.

Example of eval(Node contextNode, java.lang.String str)

eval() is used to used to get an instance of  XObject class. Using XObject instance, you can get result nodes in the form of iterator or NodeList

XObject xObject = cachedXPathAPI.eval(doc,"//person"); //Here XPath “//person” is applied on the context node doc.

NodeList nodes = xObject.nodelist();

      for(int i=0;i<nodes.getLength();i++)

      {

        Node node = nodes.item(i);

        NodeList childNodes = node.getChildNodes();

        for(int j=0;j<childNodes.getLength();j++)

        {

          if(childNodes.item(j).getNodeType()==Node.TEXT_NODE)

            System.out.println(childNodes.item(j).getNodeValue());

        }

      }

Example of selectSingleNode(Node contextNode, java.lang.String str)

selectSingleNode() is used to get a Node by applying XPath on the context node. If the given xpath returns more than one node, then only the first node will be returned.

Node node = cachedXPathAPI.selectSingleNode(doc,"//person"); //The xpath “//person” in applied on the context node

      NodeList childNodes = node.getChildNodes();

      for(int j=0;j<childNodes.getLength();j++)

      {

        if(childNodes.item(j).getNodeType()==Node.TEXT_NODE)

          System.out.println(childNodes.item(j).getNodeValue());

      }