Class XPathExpression


  • public class XPathExpression
    extends java.lang.Object
    This class is a representation of an XPath Expression for use with the XPathEvaluator class. It is modelled on the XPath API defined in JAXP 1.3, but is cut down to remove any dependencies on JAXP 1.3, making it suitable for use on vanilla JDK 1.4 installations.
    Author:
    Michael H. Kay
    • Constructor Detail

      • XPathExpression

        protected XPathExpression​(XPathEvaluator evaluator,
                                  Expression exp)
        The constructor is protected, to ensure that instances can only be created using the createExpression() method of XPathEvaluator
        Parameters:
        evaluator - the creating XPathEvaluator
        exp - the internal representation of the compiled expression
    • Method Detail

      • setStackFrameMap

        protected void setStackFrameMap​(SlotManager map,
                                        int numberOfExternalVariables)
        Define the number of slots needed for local variables within the expression
        Parameters:
        map - the stack frame map identifying all the variables used by the expression, both those declared internally, and references to variables declared externally
        numberOfExternalVariables - the number of slots in the stack frame allocated to externally-declared variables. These must be assigned a value before execution starts
      • createDynamicContext

        public XPathDynamicContext createDynamicContext​(Item contextItem)
        Create a dynamic context suitable for evaluating this expression
        Parameters:
        contextItem - the initial context item, which may be null if no context item is required, or if it is to be supplied later
        Returns:
        an XPathDynamicContext object representing a suitable dynamic context. This will be initialized with a stack frame suitable for holding the variables used by the expression.
      • iterate

        public SequenceIterator iterate​(XPathDynamicContext context)
                                 throws XPathException
        Execute the expression, returning the result as a SequenceIterator, whose members will be instances of the class Item

        Note that if evaluation of the expression fails with a dynamic error, this will generally be reported in the form of an exception thrown by the next() method of the SequenceIterator

        Parameters:
        context - the XPath dynamic context
        Returns:
        an iterator over the result of the expression
        Throws:
        XPathException
      • evaluate

        public java.util.List evaluate​(XPathDynamicContext context)
                                throws XPathException
        Execute the expression, returning the result as a List, whose members will be instances of the class Item
        Parameters:
        context - the XPath dynamic context
        Returns:
        a list of items representing the result of the expression
        Throws:
        XPathException
      • evaluateSingle

        public Item evaluateSingle​(XPathDynamicContext context)
                            throws XPathException
        Execute the expression, returning the result as a single Item If the result of the expression is a sequence containing more than one item, items after the first are discarded. If the result is an empty sequence, the method returns null.
        Parameters:
        context - the XPath dynamic context
        Returns:
        the first item in the result of the expression, or null
        Throws:
        XPathException
      • effectiveBooleanValue

        public boolean effectiveBooleanValue​(XPathDynamicContext context)
                                      throws XPathException
        Evaluate the expression, returning its effective boolean value
        Parameters:
        context - the XPath dynamic context
        Returns:
        the effective boolean value of the result, as defined by the fn:boolean() function
        Throws:
        XPathException - if a dynamic error occurs, or if the result is a value for which no effective boolean value is defined
      • evaluate

        public java.util.List evaluate​(javax.xml.transform.Source source)
                                throws XPathException
        Execute a prepared XPath expression, returning the results as a List in which items have been converted to the appropriate Java object.
        Parameters:
        source - the document or other node against which the XPath expression will be evaluated. This may be a Saxon NodeInfo object, representing a node in an existing tree, or it may be any kind of JAXP Source object such as a StreamSource SAXSource or DOMSource. For the way in which the source document is built, see Configuration.buildDocument(javax.xml.transform.Source)
        Returns:
        The results of the expression, as a List. The List represents the sequence of items returned by the expression. Each item in the list will either be an instance of net.sf.saxon.om.NodeInfo, representing a node, or a Java object representing an atomic value.
        Throws:
        XPathException
      • evaluateSingle

        public java.lang.Object evaluateSingle​(javax.xml.transform.Source source)
                                        throws XPathException
        Execute a prepared XPath expression, returning the first item in the result. This is useful where it is known that the expression will only return a singleton value (for example, a single node, or a boolean).
        Parameters:
        source - the document or other node against which the XPath expression will be evaluated. This may be a Saxon NodeInfo object, representing a node in an existing tree, or it may be any kind of JAXP Source object such as a StreamSource SAXSource or DOMSource. For the way in which the source document is built, see Configuration.buildDocument(javax.xml.transform.Source)
        Returns:
        The first item in the sequence returned by the expression. If the expression returns an empty sequence, this method returns null. Otherwise, it returns the first item in the result sequence, represented as a Java object using the same mapping as for the evaluate() method
        Throws:
        XPathException
      • rawIterator

        public SequenceIterator rawIterator​(javax.xml.transform.Source source)
                                     throws XPathException
        Get a raw iterator over the results of the expression. This returns results without any conversion of the returned items to "native" Java classes. This method is intended for use by applications that need to process the results of the expression using internal Saxon interfaces.
        Parameters:
        source - the document or other node against which the XPath expression will be evaluated. This may be a Saxon NodeInfo object, representing a node in an existing tree, or it may be any kind of JAXP Source object such as a StreamSource SAXSource or DOMSource. For the way in which the source document is built, see Configuration.buildDocument(javax.xml.transform.Source)
        Returns:
        an iterator over the results of the expression
        Throws:
        XPathException
      • getInternalExpression

        public Expression getInternalExpression()
        Low-level method to get the internal Saxon expression object. This exposes a wide range of internal methods that may be needed by specialized applications, and allows greater control over the dynamic context for evaluating the expression.
        Returns:
        the underlying Saxon expression object.