wt.util.xml.xpath.xalan2
Class XPathXalan2Impl

java.lang.Object
  wt.util.xml.xpath.xalan2.XPathXalan2Impl

All Implemented Interfaces:

XPath, XPathNI

public final class XPathXalan2Impl

extends Object

implements XPathNI

Field Summary

private static org.apache.xalan210.xalan.extensions.ExtensionsTable	xalanExtensionsTable
private org.apache.xalan210.xpath.XPath	xpath XPath expression string

Constructor Summary

XPathXalan2Impl(String xpathExprStr)

Method Summary

Object	evaluate(Node node) Evaluates the xpath relative to the specified node and returns the result as the most appropriate object.
void	evaluate(Node node, XPathCallback callback) Evaluates the xpath relative to the specified node and invokes the callback method most appropriate for the located object.
Object	evaluateAllowingIterResult(Node node) Same as XPath.evaluate(Node) except that org.w3c.dom.traversal.NodeIterator objects will be returned in place of NodeLists when the result is a node set.
private org.apache.xalan210.xpath.objects.XObject	getXObjectResult(Node node) Internal implementation of evaluate() methods.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

xpath

private org.apache.xalan210.xpath.XPath xpath

XPath expression string

xalanExtensionsTable

private static final org.apache.xalan210.xalan.extensions.ExtensionsTable xalanExtensionsTable

Constructor Detail

XPathXalan2Impl

public XPathXalan2Impl(String xpathExprStr)
                throws XPathException

Method Detail

evaluate

public void evaluate(Node node,
                     XPathCallback callback)
              throws XPathException

Description copied from interface: XPath

Evaluates the xpath relative to the specified node and invokes the callback method most appropriate for the located object.

You must supply an XPathCallback object to use this method to evaluate an XPath against a document. The XPath implementation is responsble for switching to the appropriate callback handler based on the XML nodes referenced by the XPath. This necessitates a style of programming that uses inner or anonymous class to handle the results of the XPath.

The motivation to implement XPath support this was largely to discourage styles of programming that use switches or cascading if-else-ifs where the type of the result is checked via the instanceof operator. To see how to effectively use this means of evaluation, look at the following example code.

Example

The following example evaluates the expression on the document and returns true if the xpath evaluates to a resulta and false if no result is located.

    public class SomeUtilityClass
    {
       private XPathFactory factory_ = ...;
        
       public static boolean doesXPathPointToSomething(
                Document doc_to_search,
                String x_path_expression)
          throws XPathException
       {
          // this inner class is the callback for the evaluated xpath
          class WasExpressionFoundCallback
             extends AbstractXPathCallback
          {
             private boolean wasFound = true;
             public void processNotFound() { wasFound = false; }
          };
           
          XPath x_path = factory_.newXPath(x_path_expression);
          WasExpressionFoundCallback callback = new WasExpressionFoundCallback();
          x_path.evaluate(doc_to_search, callback);
           
          return callback.wasFound;
       }
    }
 

Supported API: false

Specified by:

evaluate in interface XPath

Parameters:

node - node to search relative to

callback - interface bearing methods for each type of located object

Throws:

XPathException - implementations should rethrow all failures as XPathExceptions

See Also:

XPathCallback

evaluateAllowingIterResult

public Object evaluateAllowingIterResult(Node node)
                                  throws XPathException

Description copied from interface: XPathNI

Same as XPath.evaluate(Node) except that org.w3c.dom.traversal.NodeIterator objects will be returned in place of NodeLists when the result is a node set. This can be advantageous in that it may be more efficient in some XPath implementations.

Specified by:

evaluateAllowingIterResult in interface XPathNI

Throws:

XPathException

evaluate

public Object evaluate(Node node)
                throws XPathException

Description copied from interface: XPath

Evaluates the xpath relative to the specified node and returns the result as the most appropriate object. This will be a Double, String, Boolean, NodeList, DocumentFragment, null, or, where none of these are appropriate, an implementation specific object.

One should not use this method as an excuse to implement poor code consisting of switches or cascading if-else-ifs where the type of the result is checked via the instanceof operator. This method should only be used when a single result type is demanded.

Supported API: true

Specified by:

evaluate in interface XPath

Parameters:

node -

Returns:

Object

Throws:

XPathException

getXObjectResult

private org.apache.xalan210.xpath.objects.XObject getXObjectResult(Node node)
                                                            throws XPathException

Internal implementation of evaluate() methods.

Throws:

XPathException