See also the Document Object Model (DOM) Level 3 XPath Specification.
* * The evaluation of XPath expressions is provided by *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.
*
* @see org.w3c.dom.xpath.XPathEvaluator
*
*/
public class XPathEvaluatorImpl implements XPathEvaluator {
/**
* This prefix resolver is created whenever null is passed to the
* evaluate method. Its purpose is to satisfy the DOM L3 XPath API
* requirement that if a null prefix resolver is used, an exception
* should only be thrown when an attempt is made to resolve a prefix.
*/
class DummyPrefixResolver implements PrefixResolver {
/**
* Constructor for DummyPrefixResolver.
*/
public DummyPrefixResolver() {}
/**
* @exception DOMException
* NAMESPACE_ERR: Always throws this exceptionn
*
* @see org.apache.xml.utils.PrefixResolver#getNamespaceForPrefix(String, Node)
*/
public String getNamespaceForPrefix(String prefix, Node context) {
String fmsg = XSLMessages.createXPATHMessage(XPATHErrorResources.ER_NULL_RESOLVER, null);
throw new DOMException(DOMException.NAMESPACE_ERR, fmsg); // Unable to resolve prefix with null prefix resolver.
}
/**
* @exception DOMException
* NAMESPACE_ERR: Always throws this exceptionn
*
* @see org.apache.xml.utils.PrefixResolver#getNamespaceForPrefix(String)
*/
public String getNamespaceForPrefix(String prefix) {
return getNamespaceForPrefix(prefix,null);
}
/**
* @see org.apache.xml.utils.PrefixResolver#handlesNullPrefixes()
*/
public boolean handlesNullPrefixes() {
return false;
}
/**
* @see org.apache.xml.utils.PrefixResolver#getBaseIdentifier()
*/
public String getBaseIdentifier() {
return null;
}
}
/**
* The document to be searched to parallel the case where the XPathEvaluator
* is obtained by casting a Document.
*/
private Document m_doc = null;
/**
* Constructor for XPathEvaluatorImpl.
*/
public XPathEvaluatorImpl() {
super();
}
/**
* Constructor for XPathEvaluatorImpl.
*
* @param doc The document to be searched, to parallel the case where''
* the XPathEvaluator is obtained by casting the document.
*/
public XPathEvaluatorImpl(Document doc) {
m_doc = doc;
}
/**
* 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.
*
* @param expression The XPath expression string to be parsed.
* @param 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.
* @return The compiled form of the XPath expression.
* @exception XPathException
* INVALID_EXPRESSION_ERR: Raised if the expression is not legal
* according to the rules of the XPathEvaluatori
* @exception DOMException
* NAMESPACE_ERR: Raised if the expression contains namespace prefixes
* which cannot be resolved by the specified
* XPathNSResolver.
*
* @see org.w3c.dom.xpath.XPathEvaluator#createExpression(String, XPathNSResolver)
*/
public XPathExpression createExpression(
String expression,
XPathNSResolver resolver)
throws XPathException, DOMException {
try {
// If the resolver is null, create a dummy prefix resolver
XPath xpath = new XPath(expression,null,
((null == resolver) ? new DummyPrefixResolver() : ((PrefixResolver)resolver)),
XPath.SELECT);
return new XPathExpressionImpl(xpath, m_doc);
} catch (TransformerException e) {
throw new DOMException(XPathException.INVALID_EXPRESSION_ERR,e.getMessageAndLocation());
}
}
/**
* 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 like the DOM Level 3
* method lookupNamespaceURI on nodes in resolving the
* namespaceURI from a given prefix using the current information available
* in the node's hierarchy at the time lookupNamespaceURI is called, also
* correctly resolving the implicit xml prefix.
*
* @param nodeResolver The node to be used as a context for namespace
* resolution.
* @return XPathNSResolver which resolves namespaces with
* respect to the definitions in scope for a specified node.
*
* @see org.w3c.dom.xpath.XPathEvaluator#createNSResolver(Node)
*/
public XPathNSResolver createNSResolver(Node nodeResolver) {
return new XPathNSResolverImpl((nodeResolver.getNodeType() == Node.DOCUMENT_NODE)
? ((Document) nodeResolver).getDocumentElement() : nodeResolver);
}
/**
* Evaluates an XPath expression string and returns a result of the
* specified type if possible.
*
* @param expression The XPath expression string to be parsed and
* evaluated.
* @param 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.
* @param 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.
* @param 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.
* @param result The result specifies a specific result
* object which may be reused and returned by this method. If this is
* specified as nullor the implementation does not reuse
* the specified result, a new result object will be constructed and
* returned.For XPath 1.0 results, this object will be of type
* XPathResult.
* @return The result of the evaluation of the XPath expression.For XPath
* 1.0 results, this object will be of type XPathResult.
* @exception XPathException
* INVALID_EXPRESSION_ERR: Raised if the expression is not legal
* according to the rules of the XPathEvaluatori
* XPathNSResolver.
*