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javax.xml.xpath
Interface 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 resolver). 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 resolver). 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 nsContext).
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.

An XPath object is not thread-safe and not reentrant. In other words, it is the application's responsibility to make sure that one XPath object is not used from more than one thread at any given time, and while the evaluate method is invoked, applications may not recursively call the evaluate method.

Since:

1.5

See Also:

XML Path Language (XPath) Version 1.0

Method Summary

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

Method Detail

reset

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 obj). It is guaranteed to have a functionally equal XPathFunctionResolver, XPathVariableResolver and NamespaceContext.

setXPathVariableResolver

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.

getXPathVariableResolver

XPathVariableResolver getXPathVariableResolver()

Return the current variable resolver.

null is returned in no variable resolver is in effect.

Returns:

Current variable resolver.

setXPathFunctionResolver

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.

getXPathFunctionResolver

XPathFunctionResolver getXPathFunctionResolver()

Return the current function resolver.

null is returned in no function resolver is in effect.

Returns:

Current function resolver.

setNamespaceContext

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.

getNamespaceContext

NamespaceContext getNamespaceContext()

Return the current namespace context.

null is returned in no namespace context is in effect.

Returns:

Current Namespace context.

compile

XPathExpression compile(String expression)
                        throws XPathExpressionException

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 resovled with the XPathFunctionResolver.

If expression contains any variables, the XPathVariableResolver in effect at compile time will be used to resolve them.

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.

evaluate

Object evaluate(String expression,
                Object item,
                QName returnType)
                throws XPathExpressionException

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 (a node, 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.

evaluate

String evaluate(String expression,
                Object item)
                throws XPathExpressionException

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

This method calls evaluate(String expression, Object item, QName returnType) 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 (a node, 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.

evaluate

Object evaluate(String expression,
                InputSource source,
                QName returnType)
                throws XPathExpressionException

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 expression, Object item, QName returnType) 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.

evaluate

String evaluate(String expression,
                InputSource source)
                throws XPathExpressionException

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

This method calls evaluate(String expression, InputSource source, QName returnType) 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.