XPath provides access to the XPath evaluation environment and expressions.
The XPath evaluation is affected by the factors described in the following table.
| Factor | Behavior |
|---|---|
| context | The type of the context is implementation-dependent. If the value is null, the operation must have no dependency on the context, otherwise an XPathExpressionException will be thrown. 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:
-
Method Summary
Modifier and TypeMethodDescriptionCompile an XPath expression for later evaluation.Evaluate an XPath expression in the specified context and return the result as aString.Evaluate anXPathexpression in the specified context and return the result as the specified type.evaluate(String expression, InputSource source) Evaluate an XPath expression in the context of the specifiedInputSourceand return the result as aString.evaluate(String expression, InputSource source, QName returnType) Evaluate an XPath expression in the context of the specifiedInputSourceand return the result as the specified type.default XPathEvaluationResult<?>evaluateExpression(String expression, Object item) Evaluate an XPath expression in the specified context.default <T> TevaluateExpression(String expression, Object item, Class<T> type) Evaluate an XPath expression in the specified context and return the result with the type specified through theclass typedefault XPathEvaluationResult<?>evaluateExpression(String expression, InputSource source) Evaluate an XPath expression in the specified context.default <T> TevaluateExpression(String expression, InputSource source, Class<T> type) Evaluate an XPath expression in the context of the specifiedsourceand return the result as specified.Return the current namespace context.Return the current function resolver.Return the current variable resolver.voidreset()Reset thisXPathto its original configuration.voidsetNamespaceContext(NamespaceContext nsContext) Establish a namespace context.voidEstablish a function resolver.voidEstablish a variable resolver.
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Method Details
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reset
void reset()Reset thisXPathto its original configuration.XPathis reset to the same state as when it was created withXPathFactory.newXPath().reset()is designed to allow the reuse of existingXPaths thus saving resources associated with the creation of newXPaths.The reset
XPathis not guaranteed to have the sameXPathFunctionResolver,XPathVariableResolverorNamespaceContextObjects, e.g.Object.equals(Object obj). It is guaranteed to have a functionally equalXPathFunctionResolver,XPathVariableResolverandNamespaceContext. -
setXPathVariableResolver
Establish a variable resolver.A
NullPointerExceptionis thrown ifresolverisnull.- Parameters:
resolver- Variable resolver.- Throws:
NullPointerException- Ifresolverisnull.
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getXPathVariableResolver
XPathVariableResolver getXPathVariableResolver()Return the current variable resolver.nullis returned in no variable resolver is in effect.- Returns:
- Current variable resolver.
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setXPathFunctionResolver
Establish a function resolver.A
NullPointerExceptionis thrown ifresolverisnull.- Parameters:
resolver- XPath function resolver.- Throws:
NullPointerException- Ifresolverisnull.
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getXPathFunctionResolver
XPathFunctionResolver getXPathFunctionResolver()Return the current function resolver.nullis returned in no function resolver is in effect.- Returns:
- Current function resolver.
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setNamespaceContext
Establish a namespace context.A
NullPointerExceptionis thrown ifnsContextisnull.- Parameters:
nsContext- Namespace context to use.- Throws:
NullPointerException- IfnsContextisnull.
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getNamespaceContext
NamespaceContext getNamespaceContext()Return the current namespace context.nullis returned in no namespace context is in effect.- Returns:
- Current Namespace context.
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compile
Compile an XPath expression for later evaluation.If
expressioncontains anyXPathFunctions, they must be available via theXPathFunctionResolver. AnXPathExpressionExceptionwill be thrown if theXPathFunctioncannot be resovled with theXPathFunctionResolver.If
expressioncontains any variables, theXPathVariableResolverin effect at compile time will be used to resolve them.- Parameters:
expression- The XPath expression.- Returns:
- Compiled XPath expression.
- Throws:
XPathExpressionException- Ifexpressioncannot be compiled.NullPointerException- Ifexpressionisnull.
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evaluate
Evaluate anXPathexpression in the specified context and return the result as the specified type.See Evaluation of XPath Expressions for context item evaluation, variable, function and
QNameresolution and return type conversion.The parameter
itemrepresents the context the XPath expression will be operated on. The type of the context is implementation-dependent. If the value isnull, the operation must have no dependency on the context, otherwise an XPathExpressionException will be thrown.- Implementation Note:
- The type of the context is usually
Node. - Parameters:
expression- The XPath expression.item- The context the XPath expression will be evaluated in.returnType- The result type expected to be returned by the XPath expression.- Returns:
- The result of evaluating an XPath expression as an
ObjectofreturnType. - Throws:
XPathExpressionException- Ifexpressioncannot be evaluated.IllegalArgumentException- IfreturnTypeis not one of the types defined inXPathConstants(NUMBER,STRING,BOOLEAN,NODEorNODESET).NullPointerException- Ifexpression or returnTypeisnull.
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evaluate
Evaluate an XPath expression in the specified context and return the result as aString.This method calls
evaluate(String expression, Object item, QName returnType)with areturnTypeofXPathConstants.STRING.See Evaluation of XPath Expressions for context item evaluation, variable, function and QName resolution and return type conversion.
The parameter
itemrepresents the context the XPath expression will be operated on. The type of the context is implementation-dependent. If the value isnull, the operation must have no dependency on the context, otherwise an XPathExpressionException will be thrown.- Implementation Note:
- The type of the context is usually
Node. - Parameters:
expression- The XPath expression.item- The context the XPath expression will be evaluated in.- Returns:
- The result of evaluating an XPath expression as a
String. - Throws:
XPathExpressionException- Ifexpressioncannot be evaluated.NullPointerException- Ifexpressionisnull.
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evaluate
Object evaluate(String expression, InputSource source, QName returnType) throws XPathExpressionException Evaluate an XPath expression in the context of the specifiedInputSourceand return the result as the specified type.This method builds a data model for the
InputSourceand callsevaluate(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.
- Parameters:
expression- The XPath expression.source- The input source of the document to evaluate over.returnType- The desired return type.- Returns:
- The
Objectthat encapsulates the result of evaluating the expression. - Throws:
XPathExpressionException- If expression cannot be evaluated.IllegalArgumentException- IfreturnTypeis not one of the types defined inXPathConstants.NullPointerException- Ifexpression, source or returnTypeisnull.
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evaluate
Evaluate an XPath expression in the context of the specifiedInputSourceand return the result as aString.This method calls
evaluate(String expression, InputSource source, QName returnType)with areturnTypeofXPathConstants.STRING.See Evaluation of XPath Expressions for context item evaluation, variable, function and QName resolution and return type conversion.
- Parameters:
expression- The XPath expression.source- TheInputSourceof the document to evaluate over.- Returns:
- The
Stringthat is the result of evaluating the expression and converting the result to aString. - Throws:
XPathExpressionException- If expression cannot be evaluated.NullPointerException- Ifexpression or sourceisnull.
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evaluateExpression
default <T> T evaluateExpression(String expression, Object item, Class<T> type) throws XPathExpressionException Evaluate an XPath expression in the specified context and return the result with the type specified through theclass typeThe parameter
itemrepresents the context the XPath expression will be operated on. The type of the context is implementation-dependent. If the value isnull, the operation must have no dependency on the context, otherwise an XPathExpressionException will be thrown.- Implementation Requirements:
- The default implementation in the XPath API is equivalent to:
Since the(T)evaluate(expression, item, XPathEvaluationResult.XPathResultType.getQNameType(type));evaluatemethod does not support theANYtype, specifying XPathEvaluationResult as the type will result in IllegalArgumentException. Any implementation supporting theANYtype must override this method. - Implementation Note:
- The type of the context is usually
Node. - Type Parameters:
T- The class type that will be returned by the XPath expression.- Parameters:
expression- The XPath expression.item- The context the XPath expression will be evaluated in.type- The class type expected to be returned by the XPath expression, must be one of the types described in section 3.2 Class types in the package summary.- Returns:
- The result of evaluating the expression.
- Throws:
XPathExpressionException- If the expression cannot be evaluated.IllegalArgumentException- Iftypeis not of the types corresponding to the types defined in theXPathEvaluationResult.XPathResultType, or XPathEvaluationResult is specified as the type but an implementation supporting theANYtype is not available.NullPointerException- Ifexpression or typeisnull.- Since:
- 9
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evaluateExpression
default XPathEvaluationResult<?> evaluateExpression(String expression, Object item) throws XPathExpressionException Evaluate an XPath expression in the specified context. This is equivalent to callingevaluateExpression(String expression, Object item, Class type)with typeXPathEvaluationResult:evaluateExpression(expression, item, XPathEvaluationResult.class);The parameter
itemrepresents the context the XPath expression will be operated on. The type of the context is implementation-dependent. If the value isnull, the operation must have no dependency on the context, otherwise an XPathExpressionException will be thrown.- Implementation Requirements:
- The default implementation in the XPath API is equivalent to:
Since theevaluateExpression(expression, item, XPathEvaluationResult.class);evaluatemethod does not support theANYtype, the default implementation of this method will always throw an IllegalArgumentException. Any implementation supporting theANYtype must therefore override this method. - Implementation Note:
- The type of the context is usually
Node. - Parameters:
expression- The XPath expression.item- The context the XPath expression will be evaluated in.- Returns:
- The result of evaluating the expression.
- Throws:
XPathExpressionException- If the expression cannot be evaluated.IllegalArgumentException- If the implementation of this method does not support theANYtype.NullPointerException- Ifexpressionisnull.- Since:
- 9
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evaluateExpression
default <T> T evaluateExpression(String expression, InputSource source, Class<T> type) throws XPathExpressionException Evaluate an XPath expression in the context of the specifiedsourceand return the result as specified.This method builds a data model for the
InputSourceand callsevaluateExpression(String expression, Object item, Class type)on the resulting document object. The data model is usuallyDocument- Implementation Requirements:
- The default implementation in the XPath API is equivalent to:
Since the(T)evaluate(expression, source, XPathEvaluationResult.XPathResultType.getQNameType(type));evaluatemethod does not support theANYtype, specifying XPathEvaluationResult as the type will result in IllegalArgumentException. Any implementation supporting theANYtype must override this method. - Type Parameters:
T- The class type that will be returned by the XPath expression.- Parameters:
expression- The XPath expression.source- The input source of the document to evaluate over.type- The class type expected to be returned by the XPath expression, must be one of the types described in section 3.2 Class types in the package summary.- Returns:
- The result of evaluating the expression.
- Throws:
XPathExpressionException- If the expression cannot be evaluated.IllegalArgumentException- Iftypeis not of the types corresponding to the types defined in theXPathResultType, or XPathEvaluationResult is specified as the type but an implementation supporting theANYtype is not available.NullPointerException- Ifexpression, source or typeisnull.- Since:
- 9
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evaluateExpression
default XPathEvaluationResult<?> evaluateExpression(String expression, InputSource source) throws XPathExpressionException Evaluate an XPath expression in the specified context. This is equivalent to callingevaluateExpression(String expression, Object item, Class type)with typeXPathEvaluationResult:evaluateExpression(expression, item, XPathEvaluationResult.class);- Implementation Requirements:
- The default implementation in the XPath API is equivalent to:
Since theevaluateExpression(expression, source, XPathEvaluationResult.class);evaluatemethod does not support theANYtype, the default implementation of this method will always throw an IllegalArgumentException. Any implementation supporting theANYtype must therefore override this method. - Parameters:
expression- The XPath expression.source- The input source of the document to evaluate over.- Returns:
- The result of evaluating the expression.
- Throws:
XPathExpressionException- If the expression cannot be evaluated.IllegalArgumentException- If the implementation of this method does not support theANYtype.NullPointerException- Ifexpression or sourceisnull.- Since:
- 9
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