org.jdom.xpath
Class XPath

java.lang.Object
  |
  +--org.jdom.xpath.XPath

public abstract class XPath

extends java.lang.Object

implements java.io.Serializable

A utility class for performing XPath calls on JDOM nodes, with a factory interface for obtaining a first XPath instance. Users operate against this class while XPath vendors can plug-in implementations underneath. Users can choose an implementation using either setXPathClass(java.lang.Class) or the system property "org.jdom.xpath.class".

Version:

$Revision: 1.15 $, $Date: 2004/02/06 09:28:32 $

Author:

Laurent Bihanic

See Also:

Serialized Form

Constructor Summary

XPath()

Method Summary

abstract void	addNamespace(Namespace namespace) Adds a namespace definition to the list of namespaces known of this XPath expression.
void	addNamespace(java.lang.String prefix, java.lang.String uri) Adds a namespace definition (prefix and URI) to the list of namespaces known of this XPath expression.
abstract java.lang.String	getXPath() Returns the wrapped XPath expression as a string.
static XPath	newInstance(java.lang.String path) Creates a new XPath wrapper object, compiling the specified XPath expression.
abstract java.lang.Number	numberValueOf(java.lang.Object context) Returns the number value of the first node selected by applying the wrapped XPath expression to the given context.
abstract java.util.List	selectNodes(java.lang.Object context) Evaluates the wrapped XPath expression and returns the list of selected items.
static java.util.List	selectNodes(java.lang.Object context, java.lang.String path) Evaluates an XPath expression and returns the list of selected items.
abstract java.lang.Object	selectSingleNode(java.lang.Object context) Evaluates the wrapped XPath expression and returns the first entry in the list of selected nodes (or atomics).
static java.lang.Object	selectSingleNode(java.lang.Object context, java.lang.String path) Evaluates the wrapped XPath expression and returns the first entry in the list of selected nodes (or atomics).
abstract void	setVariable(java.lang.String name, java.lang.Object value) Defines an XPath variable and sets its value.
static void	setXPathClass(java.lang.Class aClass) Sets the concrete XPath subclass to use when allocating XPath instances.
abstract java.lang.String	valueOf(java.lang.Object context) Returns the string value of the first node selected by applying the wrapped XPath expression to the given context.
protected java.lang.Object	writeReplace() [Serialization support] Returns the alternative object to write to the stream when serializing this object.

Methods inherited from class java.lang.Object

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

Constructor Detail

XPath

public XPath()

Method Detail

newInstance

public static XPath newInstance(java.lang.String path)
                         throws JDOMException

Creates a new XPath wrapper object, compiling the specified XPath expression.

Parameters:

path - the XPath expression to wrap.

Throws:

JDOMException - if the XPath expression is invalid.

setXPathClass

public static void setXPathClass(java.lang.Class aClass)
                          throws JDOMException

Sets the concrete XPath subclass to use when allocating XPath instances.

Parameters:

aClass - the concrete subclass of XPath.

Throws:

java.lang.IllegalArgumentException - if aClass is null.

JDOMException - if aClass is not a concrete subclass of XPath.

selectNodes

public abstract java.util.List selectNodes(java.lang.Object context)
                                    throws JDOMException

Evaluates the wrapped XPath expression and returns the list of selected items.

Parameters:

context - the node to use as context for evaluating the XPath expression.

Returns:

the list of selected items, which may be of types: Element, Attribute, Text, CDATA, Comment, ProcessingInstruction, Boolean, Double, or String.

Throws:

JDOMException - if the evaluation of the XPath expression on the specified context failed.

selectSingleNode

public abstract java.lang.Object selectSingleNode(java.lang.Object context)
                                           throws JDOMException

Evaluates the wrapped XPath expression and returns the first entry in the list of selected nodes (or atomics).

Parameters:

context - the node to use as context for evaluating the XPath expression.

Returns:

the first selected item, which may be of types: Element, Attribute, Text, CDATA, Comment, ProcessingInstruction, Boolean, Double, String, or null if no item was selected.

Throws:

JDOMException - if the evaluation of the XPath expression on the specified context failed.

valueOf

public abstract java.lang.String valueOf(java.lang.Object context)
                                  throws JDOMException

Returns the string value of the first node selected by applying the wrapped XPath expression to the given context.

Parameters:

context - the element to use as context for evaluating the XPath expression.

Returns:

the string value of the first node selected by applying the wrapped XPath expression to the given context.

Throws:

JDOMException - if the XPath expression is invalid or its evaluation on the specified context failed.

numberValueOf

public abstract java.lang.Number numberValueOf(java.lang.Object context)
                                        throws JDOMException

Returns the number value of the first node selected by applying the wrapped XPath expression to the given context.

Parameters:

context - the element to use as context for evaluating the XPath expression.

Returns:

the number value of the first node selected by applying the wrapped XPath expression to the given context, null if no node was selected or the special value java.lang.Double#NaN (Not-a-Number) if the selected value can not be converted into a number value.

Throws:

JDOMException - if the XPath expression is invalid or its evaluation on the specified context failed.

setVariable

public abstract void setVariable(java.lang.String name,
                                 java.lang.Object value)

Defines an XPath variable and sets its value.

Parameters:

name - the variable name.

value - the variable value.

Throws:

java.lang.IllegalArgumentException - if name is not a valid XPath variable name or if the value type is not supported by the underlying implementation

addNamespace

public abstract void addNamespace(Namespace namespace)

Adds a namespace definition to the list of namespaces known of this XPath expression.

Note: In XPath, there is no such thing as a 'default namespace'. The empty prefix always resolves to the empty namespace URI.

Parameters:

namespace - the namespace.

addNamespace

public void addNamespace(java.lang.String prefix,
                         java.lang.String uri)

Adds a namespace definition (prefix and URI) to the list of namespaces known of this XPath expression.

Note: In XPath, there is no such thing as a 'default namespace'. The empty prefix always resolves to the empty namespace URI.

Parameters:

prefix - the namespace prefix.

uri - the namespace URI.

Throws:

IllegalNameException - if the prefix or uri are null or empty strings or if they contain illegal characters.

getXPath

public abstract java.lang.String getXPath()

Returns the wrapped XPath expression as a string.

Returns:

the wrapped XPath expression as a string.

selectNodes

public static java.util.List selectNodes(java.lang.Object context,
                                         java.lang.String path)
                                  throws JDOMException

Evaluates an XPath expression and returns the list of selected items.

Note: This method should not be used when the same XPath expression needs to be applied several times (on the same or different contexts) as it requires the expression to be compiled before being evaluated. In such cases, allocating an XPath wrapper instance and evaluating it several times is way more efficient.

Parameters:

context - the node to use as context for evaluating the XPath expression.

path - the XPath expression to evaluate.

Returns:

the list of selected items, which may be of types: Element, Attribute, Text, CDATA, Comment, ProcessingInstruction, Boolean, Double, or String.

Throws:

JDOMException - if the XPath expression is invalid or its evaluation on the specified context failed.

selectSingleNode

public static java.lang.Object selectSingleNode(java.lang.Object context,
                                                java.lang.String path)
                                         throws JDOMException

Evaluates the wrapped XPath expression and returns the first entry in the list of selected nodes (or atomics).

Note: This method should not be used when the same XPath expression needs to be applied several times (on the same or different contexts) as it requires the expression to be compiled before being evaluated. In such cases, allocating an XPath wrapper instance and evaluating it several times is way more efficient.

Parameters:

context - the element to use as context for evaluating the XPath expression.

path - the XPath expression to evaluate.

Returns:

the first selected item, which may be of types: Element, Attribute, Text, CDATA, Comment, ProcessingInstruction, Boolean, Double, String, or null if no item was selected.

Throws:

JDOMException - if the XPath expression is invalid or its evaluation on the specified context failed.

writeReplace

protected final java.lang.Object writeReplace()
                                       throws java.io.ObjectStreamException

[Serialization support] Returns the alternative object to write to the stream when serializing this object. This method returns an instance of a dedicated nested class to serialize XPath expressions independently of the concrete implementation being used.

Note: Subclasses are not allowed to override this method to ensure valid serialization of all implementations.

Returns:

an XPathString instance configured with the wrapped XPath expression.

Throws:

java.io.ObjectStreamException - never.