org.w3c.dom.xpath
Interface XPathEvaluator


public interface XPathEvaluator

DOM Level 3 WD Experimental: The DOM Level 3 specification is at the stage of Working Draft, which represents work in progress and thus may be updated, replaced, or obsoleted by other documents at any time.

XPathEvaluator, which will provide evaluation of XPath 1.0 expressions with no specialized extension functions or variables. It is expected that the XPathEvaluator interface will be implemented on the same object which implements the Document interface in an implementation which supports the XPath DOM module. XPathEvaluator implementations may be available from other sources that may provide support for special extension functions or variables which are not defined in this specification. The methods of XPathExpression should be named with more-XPath- specific names because the interface will often be implemented by the same object which implements document.No change.The point of interfaces is to localize the implementing namespace. This would make the method names unnecessarily long and complex even though there are no conflicts in the interface itself. The new core method getInterface is designed for discovering interfaces of additional modules that may not be directly implemented on the objects to which they are attached. This could be used to implement XPath on a separate object. The user only refers to the separate interfaces and not the proprietary aggregate implementation.Should entity refs be supported so that queries can be made on them?No change.We will not do this now. They are not part of the XPath data model. Note that they may be present in the hierarchy of returned nodes, but may not directly be requested or returned in the node set.What does createResult create when one wants to reuse the XPath?It is not useful.Removed method. Should ordering be a separate flag, or a type of result that can be requested. As a type of result, it can be better optimized in implementations.It makes sense as a type of result. Changed.Removed method.Implementing XPathEvaluator on Document can be a problem due to conflicts in the names of the methods.The working group finds no better solution. GetInterface in Level 3 permits the object to be implemented separately. We should be committed to this. We will leave this issue open to see if we get more feedback on it.How does this interface adapt to XPath 2.0 and other query languages.No change.This interface is not intended to adapt to XPath 2.0 or other languages. The models of these are likely to be incompatible enough to require new APIs.For alternate implementations that can use this API, it can be obtained from different sources.Support for custom variables and functions would be very useful. No change.It is possible for an implementation to supply alternative sources of an XPathEvaluator that can be customized with a custom variable and function context. We do not specify how this is accomplished. It is too complex to address in this version of the XPath DOM.

See also the Document Object Model (DOM) Level 3 XPath Specification.


Method Summary
 XPathExpression createExpression(java.lang.String expression, XPathNSResolver resolver)
          Creates a parsed XPath expression with resolved namespaces.
 XPathNSResolver createNSResolver(Node nodeResolver)
          Adapts any DOM node to resolve namespaces so that an XPath expression can be easily evaluated relative to the context of the node where it appeared within the document.
 java.lang.Object evaluate(java.lang.String expression, Node contextNode, XPathNSResolver resolver, short type, java.lang.Object result)
          Evaluates an XPath expression string and returns a result of the specified type if possible.An exception needs to be raised when an XPath expression is evaluated on a node such as an EntityReference which cannot serve as an XPath context node.Done: NOT_SUPPORTED_ERR.A description is needed of what happens when the node passed to the evaluation function is a Text or CDATASection in the DOM case where the text may be fragmented between text nodes.Done.Eliminate the evaluate method from XPathEvaluator, forcing everyone to create expressions.No change.Any implementor can easily implement it by creating an expression.
 

Method Detail

createExpression

public XPathExpression createExpression(java.lang.String expression,
                                        XPathNSResolver resolver)
                                 throws XPathException,
                                        DOMException
Creates a parsed XPath expression with resolved namespaces. This is useful when an expression will be reused in an application since it makes it possible to compile the expression string into a more efficient internal form and preresolve all namespace prefixes which occur within the expression.createExpression should not raise exceptions about type coercion.This was already fixed in the public draft.

Parameters:
expression - The XPath expression string to be parsed.
resolver - The resolver permits translation of prefixes within the XPath expression into appropriate namespace URIs . If this is specified as null, any namespace prefix within the expression will result in DOMException being thrown with the code NAMESPACE_ERR.
Returns:
The compiled form of the XPath expression.
Throws:
XPathException - INVALID_EXPRESSION_ERR: Raised if the expression is not legal according to the rules of the XPathEvaluatori
DOMException - NAMESPACE_ERR: Raised if the expression contains namespace prefixes which cannot be resolved by the specified XPathNSResolver.

createNSResolver

public XPathNSResolver createNSResolver(Node nodeResolver)
Adapts any DOM node to resolve namespaces so that an XPath expression can be easily evaluated relative to the context of the node where it appeared within the document. This adapter works by calling the method lookupNamespacePrefix on Node.It should be possible to create an XPathNSResolver that does not rely on a node, but which implements a map of resolutions that can be added to by the application.No change.The application can easily create this, which was why the interface was designed as it is. The specification will not require a specific factory at this time for application populated maps.There should be type restrictions on which types of nodes may be adapted by createNSResolver.No change.The namespace methods on the Node interface of the Level 3 core may be called without exception on all node types. In some cases no non-null namespace resolution will ever be returned. That is what may also be expected of this adapter.

Parameters:
nodeResolver - The node to be used as a context for namespace resolution.
Returns:
XPathNSResolver which resolves namespaces with respect to the definitions in scope for a specified node.

evaluate

public java.lang.Object evaluate(java.lang.String expression,
                                 Node contextNode,
                                 XPathNSResolver resolver,
                                 short type,
                                 java.lang.Object result)
                          throws XPathException,
                                 DOMException
Evaluates an XPath expression string and returns a result of the specified type if possible.An exception needs to be raised when an XPath expression is evaluated on a node such as an EntityReference which cannot serve as an XPath context node.Done: NOT_SUPPORTED_ERR.A description is needed of what happens when the node passed to the evaluation function is a Text or CDATASection in the DOM case where the text may be fragmented between text nodes.Done.Eliminate the evaluate method from XPathEvaluator, forcing everyone to create expressions.No change.Any implementor can easily implement it by creating an expression. Having it available as a separate routine is a convenience and may be an optimization as well in some cases.Revert to multiple evaluateAs methods instead of passing a type code.No change.This is an alternative which eliminates a method argument while adding methods, but the type code is used to designate the type on returns anyway and using it as an argument to specify any coercion seems natural to many.Error exceptions are needed when there is a mismatch between the implementation of XPathEvaluator and the context node being evaluated.Done: WRONG_DOCUMENT_ERRConcern that the XPath API should only support natural results of XPath expression, without convenience coercion or alternative representations. Any special thing such as ordering should be added later to resultNo change.We have significant use cases for returning alternative types and representations by explicit request in advance.Eliminate the reusable result argument.No change.No. We have use cases for it, and there is already an implementation showing there is nothing wrong with it. State that the XPathNSResolver argument may be a function in Javascript.Yes.There is an exception when there is a problem parsing the expression, but none when there is a problem evaluating the expression.No change.If the expression parsing was OK, then the worst that can happen is an empty result is returned.When requesting any type, the implementation should be permitted to return any type of node set, i.e. ordered or unordered, it finds convenient.No change. The iterator it returns may contain ordered results, but identifying it as such produces undesirable results, because it would create complexity for the user -- requiring checking two types to see if the result was a node set -- or incompatibility caused by assuming it was always the one returned by a particular implementation the developer was using.NAMESPACE_ERR description is not appropriate to the way it is being used here.Make the description of NAMESPACE_ERR in the core specification more general.Should the INVALID_EXPRESSION_ERR be INVALID_SYNTAX_ERR?No change.We can improve the description of the error, but the name is appropriate as-is. It covers not only syntax errors but expression errors, such as when the implementation has no custom functions or variables but the expression specifies custom functions or variables.

Parameters:
expression - The XPath expression string to be parsed and evaluated.
contextNode - The context is context node for the evaluation of this XPath expression. If the XPathEvaluator was obtained by casting the Document then this must be owned by the same document and must be a Document, Element, Attribute, Text, CDATASection, Comment, ProcessingInstruction, or XPathNamespace node. If the context node is a Text or a CDATASection, then the context is interpreted as the whole logical text node as seen by XPath, unless the node is empty in which case it may not serve as the XPath context.
resolver - The resolver permits translation of prefixes within the XPath expression into appropriate namespace URIs . If this is specified as null, any namespace prefix within the expression will result in DOMException being thrown with the code NAMESPACE_ERR.
type - If a specific type is specified, then the result will be coerced to return the specified type relying on XPath type conversions and fail if the desired coercion is not possible. This must be one of the type codes of XPathResult.
result - The result specifies a specific XPathResult which may be reused and returned by this method. If this is specified as nullor the implementation cannot reuse the specified result, a new XPathResult will be constructed and returned.
Returns:
The result of the evaluation of the XPath expression.
Throws:
XPathException - INVALID_EXPRESSION_ERR: Raised if the expression is not legal according to the rules of the XPathEvaluatori
TYPE_ERR: Raised if the result cannot be converted to return the specified type.
DOMException - NAMESPACE_ERR: Raised if the expression contains namespace prefixes which cannot be resolved by the specified XPathNSResolver.
WRONG_DOCUMENT_ERR: The Node is from a document that is not supported by this XPathEvaluator.
NOT_SUPPORTED_ERR: The Node is not a type permitted as an XPath context node.


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