XPath

public interface XPath

XPath provides access to the XPath evaluation environment and expressions.

Evaluation of XPath Expressions.
context	If a request is made to evaluate the expression in the absence of a context item, an empty document node will be used for the context. For the purposes of evaluating XPath expressions, a DocumentFragment is treated like a Document node.
variables	If the expression contains a variable reference, its value will be found through the XPathVariableResolver set with setXPathVariableResolver(XPathVariableResolver). An XPathExpressionException is raised if the variable resolver is undefined or the resolver returns null for the variable. The value of a variable must be immutable through the course of any single evaluation.
functions	If the expression contains a function reference, the function will be found through the XPathFunctionResolver set with setXPathFunctionResolver(XPathFunctionResolver). An XPathExpressionException is raised if the function resolver is undefined or the function resolver returns null for the function.
QNames	QNames in the expression are resolved against the XPath namespace context set with setNamespaceContext(NamespaceContext).
result	This result of evaluating an expression is converted to an instance of the desired return type. Valid return types are defined in XPathConstants. Conversion to the return type follows XPath conversion rules.

See Also

• XML Path Language (XPath) Version 1.0

Public Method Summary

abstract XPathExpression	compile(String expression) Compile an XPath expression for later evaluation.
abstract Object	evaluate(String expression, Object item, QName returnType) Evaluate an XPath expression in the specified context and return the result as the specified type.
abstract String	evaluate(String expression, Object item) Evaluate an XPath expression in the specified context and return the result as a String.
abstract Object	evaluate(String expression, InputSource source, QName returnType) Evaluate an XPath expression in the context of the specified InputSource and return the result as the specified type.
abstract String	evaluate(String expression, InputSource source) Evaluate an XPath expression in the context of the specified InputSource and return the result as a String.
abstract NamespaceContext	getNamespaceContext() Return the current namespace context.
abstract XPathFunctionResolver	getXPathFunctionResolver() Return the current function resolver.
abstract XPathVariableResolver	getXPathVariableResolver() Return the current variable resolver.
abstract void	reset() Reset this XPath to its original configuration.
abstract void	setNamespaceContext(NamespaceContext nsContext) Establish a namespace context.
abstract void	setXPathFunctionResolver(XPathFunctionResolver resolver) Establish a function resolver.
abstract void	setXPathVariableResolver(XPathVariableResolver resolver) Establish a variable resolver.

Public Methods

public abstract XPathExpression compile (String expression)

Compile an XPath expression for later evaluation.

If expression contains any XPathFunctions, they must be available via the XPathFunctionResolver. An XPathExpressionException will be thrown if the XPathFunction cannot be resolved with the XPathFunctionResolver.

If expression is null, a NullPointerException is thrown.

Parameters

expression	The XPath expression.

Returns

• Compiled XPath expression.

Throws

XPathExpressionException	If expression cannot be compiled.
NullPointerException	If expression is null.

public abstract Object evaluate (String expression, Object item, QName returnType)

Evaluate an XPath expression in the specified context and return the result as the specified type.

See Evaluation of XPath Expressions for context item evaluation, variable, function and QName resolution and return type conversion.

If returnType is not one of the types defined in XPathConstants ( NUMBER, STRING, BOOLEAN, NODE or NODESET) then an IllegalArgumentException is thrown.

If a null value is provided for item, an empty document will be used for the context. If expression or returnType is null, then a NullPointerException is thrown.

Parameters

expression	The XPath expression.
item	The starting context (node or node list, for example).
returnType	The desired return type.

Returns

• Result of evaluating an XPath expression as an Object of returnType.

Throws

XPathExpressionException	If expression cannot be evaluated.
IllegalArgumentException	If returnType is not one of the types defined in XPathConstants.
NullPointerException	If expression or returnType is null.

public abstract String evaluate (String expression, Object item)

Evaluate an XPath expression in the specified context and return the result as a String.

This method calls evaluate(String, Object, QName) with a returnType of XPathConstants.STRING.

See Evaluation of XPath Expressions for context item evaluation, variable, function and QName resolution and return type conversion.

If a null value is provided for item, an empty document will be used for the context. If expression is null, then a NullPointerException is thrown.

Parameters

expression	The XPath expression.
item	The starting context (node or node list, for example).

Returns

• The String that is the result of evaluating the expression and converting the result to a String.

Throws

XPathExpressionException	If expression cannot be evaluated.
NullPointerException	If expression is null.

public abstract Object evaluate (String expression, InputSource source, QName returnType)

Evaluate an XPath expression in the context of the specified InputSource and return the result as the specified type.

This method builds a data model for the InputSource and calls evaluate(String, Object, QName) on the resulting document object.

See Evaluation of XPath Expressions for context item evaluation, variable, function and QName resolution and return type conversion.

If returnType is not one of the types defined in XPathConstants, then an IllegalArgumentException is thrown.

If expression, source or returnType is null, then a NullPointerException is thrown.

Parameters

expression	The XPath expression.
source	The input source of the document to evaluate over.
returnType	The desired return type.

Returns

• The Object that encapsulates the result of evaluating the expression.

Throws

XPathExpressionException	If expression cannot be evaluated.
IllegalArgumentException	If returnType is not one of the types defined in XPathConstants.
NullPointerException	If expression, source or returnType is null.

public abstract String evaluate (String expression, InputSource source)

Evaluate an XPath expression in the context of the specified InputSource and return the result as a String.

This method calls evaluate(String, InputSource, QName) with a returnType of XPathConstants.STRING.

See Evaluation of XPath Expressions for context item evaluation, variable, function and QName resolution and return type conversion.

If expression or source is null, then a NullPointerException is thrown.

Parameters

expression	The XPath expression.
source	The InputSource of the document to evaluate over.

Returns

• The String that is the result of evaluating the expression and converting the result to a String.

Throws

XPathExpressionException	If expression cannot be evaluated.
NullPointerException	If expression or source is null.

public abstract NamespaceContext getNamespaceContext ()

Return the current namespace context.

null is returned in no namespace context is in effect.

Returns

• Current Namespace context.

public abstract XPathFunctionResolver getXPathFunctionResolver ()

Return the current function resolver.

null is returned in no function resolver is in effect.

Returns

• Current function resolver.

public abstract XPathVariableResolver getXPathVariableResolver ()

Return the current variable resolver.

null is returned in no variable resolver is in effect.

Returns

• Current variable resolver.

public abstract void reset ()

Reset this XPath to its original configuration.

XPath is reset to the same state as when it was created with XPathFactory.newXPath(). reset() is designed to allow the reuse of existing XPaths thus saving resources associated with the creation of new XPaths.

The reset XPath is not guaranteed to have the same XPathFunctionResolver, XPathVariableResolver or NamespaceContext Objects, e.g. Object.equals(Object). It is guaranteed to have a functionally equal XPathFunctionResolver, XPathVariableResolver and NamespaceContext.

public abstract void setNamespaceContext (NamespaceContext nsContext)

Establish a namespace context.

A NullPointerException is thrown if nsContext is null.

Parameters

nsContext	Namespace context to use.

Throws

NullPointerException	If nsContext is null.

public abstract void setXPathFunctionResolver (XPathFunctionResolver resolver)

Establish a function resolver.

A NullPointerException is thrown if resolver is null.

Parameters

resolver	XPath function resolver.

Throws

NullPointerException	If resolver is null.

public abstract void setXPathVariableResolver (XPathVariableResolver resolver)

Establish a variable resolver.

A NullPointerException is thrown if resolver is null.

Parameters

resolver	Variable resolver.

Throws

NullPointerException	If resolver is null.