net.sf.saxon.s9api
Class XPathSelector

java.lang.Object
  net.sf.saxon.s9api.XPathSelector

All Implemented Interfaces:

Iterable<XdmItem>

public class XPathSelector
extends Object
implements Iterable<XdmItem>

An XPathSelector represents a compiled and loaded XPath expression ready for execution. The XPathSelector holds details of the dynamic evaluation context for the XPath expression.

Method Summary

XdmValue	evaluate() Evaluate the expression, returning the result as an XdmValue (that is, a sequence of nodes and/or atomic values).
XdmItem	evaluateSingle() Evaluate the XPath expression, returning the result as an XdmItem (that is, a single node or atomic value).
XdmItem	getContextItem() Get the context item used for evaluating the XPath expression.
Iterator<XdmItem>	iterator() Evaluate the expression, returning the result as an Iterator (that is, an iterator over a sequence of nodes and/or atomic values).
void	setContextItem(XdmItem item) Set the context item for evaluating the XPath expression.
void	setVariable(QName name, XdmValue value) Set the value of a variable

Methods inherited from class java.lang.Object

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

Method Detail

setContextItem

public void setContextItem(XdmItem item)
                    throws SaxonApiException

Set the context item for evaluating the XPath expression. This may be either a node or an atomic value. Most commonly it will be a document node, which might be constructed using the DocumentBuilder.build(javax.xml.transform.Source) method.

Parameters:

item - The context item for evaluating the expression. Must not be null.

Throws:

SaxonApiException

getContextItem

public XdmItem getContextItem()

Get the context item used for evaluating the XPath expression. This may be either a node or an atomic value. Most commonly it will be a document node, which might be constructed using the Build method of the DocumentBuilder object.

Returns:

The context item for evaluating the expression, or null if no context item has been set.

setVariable

public void setVariable(QName name,
                        XdmValue value)
                 throws SaxonApiException

Set the value of a variable

Parameters:

name - The name of the variable. This must match the name of a variable that was declared to the XPathCompiler. No error occurs if the expression does not actually reference a variable with this name.

value - The value to be given to the variable.

Throws:

SaxonApiException - if the variable has not been declared or if the type of the value supplied does not conform to the required type that was specified when the variable was declared

evaluate

public XdmValue evaluate()
                  throws SaxonApiException

Evaluate the expression, returning the result as an XdmValue (that is, a sequence of nodes and/or atomic values).

Note: Although a singleton result may be represented as an XdmItem, there is no guarantee that this will always be the case. If you know that the expression will return at most one node or atomic value, it is best to use the evaluateSingle method, which does guarantee that an XdmItem (or null) will be returned.

Returns:

An XdmValue representing the results of the expression.

Throws:

SaxonApiException - if a dynamic error occurs during the expression evaluation.

evaluateSingle

public XdmItem evaluateSingle()
                       throws SaxonApiException

Evaluate the XPath expression, returning the result as an XdmItem (that is, a single node or atomic value).

Returns:

an XdmItem representing the result of the expression, or null if the expression returns an empty sequence. If the expression returns a sequence of more than one item, any items after the first are ignored.

Throws:

SaxonApiException - if a dynamic error occurs during the expression evaluation.

iterator

public Iterator<XdmItem> iterator()
                           throws SaxonApiUncheckedException

Evaluate the expression, returning the result as an Iterator (that is, an iterator over a sequence of nodes and/or atomic values).

Because an XPathSelector is an Iterable, it is possible to iterate over the result using a Java 5 "for each" expression, for example:

 XPathCompiler compiler = processor.newXPathCompiler();
 XPathSelector seq = compiler.compile("1 to 20").load();
 for (XdmItem item : seq) {
   System.err.println(item);
 }
 

Specified by:

iterator in interface Iterable<XdmItem>

Returns:

An iterator over the sequence that represents the results of the expression. Each object in this sequence will be an instance of XdmItem. Note that the expression may be evaluated lazily, which means that a successful response from this method does not imply that the expression has executed successfully: failures may be reported later while retrieving items from the iterator.

Throws:

SaxonApiUncheckedException - if a dynamic error occurs during XPath evaluation that can be detected at this point. It is also possible that an SaxonApiUncheckedException will be thrown by the hasNext() method of the returned iterator.