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XPathExpression (Java Platform SE 6) - JDK 5 Documentation v6.0, Java 2 SDK 英文文档

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javax.xml.xpath
Interface XPathExpression

public interface XPathExpression

XPathExpression provides access to compiled XPath 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. 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. 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.
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 expression is not thread-safe and not reentrant. In other words, it is the application's responsibility to make sure that one XPathExpression 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, Expressions

Method Summary
 String evaluate(InputSource source)
          Evaluate the compiled XPath expression in the context of the specified InputSource and return the result as a String.
 Object evaluate(InputSource source, QName returnType)
          Evaluate the compiled XPath expression in the context of the specified InputSource and return the result as the specified type.
 String evaluate(Object item)
          Evaluate the compiled XPath expression in the specified context and return the result as a String.
 Object evaluate(Object item, QName returnType)
          Evaluate the compiled XPath expression in the specified context and return the result as the specified type.
 

Method Detail

evaluate

Object evaluate(Object item,
                QName returnType)
                throws XPathExpressionException

Evaluate the compiled 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, then an IllegalArgumentException is thrown.

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

Parameters:
item - The starting context (a node, for example).
returnType - The desired return type.
Returns:
The Object that is the result of evaluating the expression and converting the result to returnType.
Throws:
XPathExpressionException - If the expression cannot be evaluated.
IllegalArgumentException - If returnType is not one of the types defined in XPathConstants.
NullPointerException - If returnType is null.

evaluate

String evaluate(Object item)
                throws XPathExpressionException

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

This method calls evaluate(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.

Parameters:
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 the expression cannot be evaluated.

evaluate

Object evaluate(InputSource source,
                QName returnType)
                throws XPathExpressionException

Evaluate the compiled 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(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 source or returnType is null, then a NullPointerException is thrown.

Parameters:
source - The InputSource of the document to evaluate over.
returnType - The desired return type.
Returns:
The Object that is the result of evaluating the expression and converting the result to returnType.
Throws:
XPathExpressionException - If the expression cannot be evaluated.
IllegalArgumentException - If returnType is not one of the types defined in XPathConstants.
NullPointerException - If source or returnType is null.

evaluate

String evaluate(InputSource source)
                throws XPathExpressionException

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

This method calls evaluate(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 source is null, then a NullPointerException is thrown.

Parameters:
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 the expression cannot be evaluated.
NullPointerException - If source is null.
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