341 lines
13 KiB
Java
341 lines
13 KiB
Java
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/*
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* Licensed to the Apache Software Foundation (ASF) under one
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* or more contributor license agreements. See the NOTICE file
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* distributed with this work for additional information
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* regarding copyright ownership. The ASF licenses this file
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* to you under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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/*
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* $Id: CachedXPathAPI.java 524811 2007-04-02 15:51:59Z zongaro $
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*/
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package org.apache.xpath;
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import javax.xml.transform.TransformerException;
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import org.apache.xml.utils.PrefixResolver;
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import org.apache.xml.utils.PrefixResolverDefault;
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import org.apache.xpath.objects.XObject;
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import org.w3c.dom.Document;
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import org.w3c.dom.Node;
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import org.w3c.dom.NodeList;
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import org.w3c.dom.traversal.NodeIterator;
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/**
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* The methods in this class are convenience methods into the
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* low-level XPath API.
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*
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* These functions tend to be a little slow, since a number of objects must be
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* created for each evaluation. A faster way is to precompile the
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* XPaths using the low-level API, and then just use the XPaths
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* over and over.
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*
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* This is an alternative for the old XPathAPI class, which provided
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* static methods for the purpose but had the drawback of
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* instantiating a new XPathContext (and thus building a new DTMManager,
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* and new DTMs) each time it was called. XPathAPIObject instead retains
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* its context as long as the object persists, reusing the DTMs. This
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* does have a downside: if you've changed your source document, you should
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* obtain a new XPathAPIObject to continue searching it, since trying to use
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* the old DTMs will probably yield bad results or malfunction outright... and
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* the cached DTMs may consume memory until this object and its context are
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* returned to the heap. Essentially, it's the caller's responsibility to
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* decide when to discard the cache.
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*
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* @see <a href="http://www.w3.org/TR/xpath">XPath Specification</a>
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* */
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public class CachedXPathAPI
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{
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/** XPathContext, and thus the document model system (DTMs), persists through multiple
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calls to this object. This is set in the constructor.
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*/
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protected XPathContext xpathSupport;
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/**
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* <p>Default constructor. Establishes its own {@link XPathContext}, and hence
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* its own {@link org.apache.xml.dtm.DTMManager}.
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* Good choice for simple uses.</p>
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* <p>Note that any particular instance of {@link CachedXPathAPI} must not be
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* operated upon by multiple threads without synchronization; we do
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* not currently support multithreaded access to a single
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* {@link org.apache.xml.dtm.DTM}.</p>
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*/
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public CachedXPathAPI()
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{
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// Create an XPathContext that doesn't support pushing and popping of
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// variable resolution scopes. Sufficient for simple XPath 1.0 expressions.
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xpathSupport = new XPathContext(false);
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}
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/**
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* <p>This constructor shares its {@link XPathContext} with a pre-existing
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* {@link CachedXPathAPI}. That allows sharing document models
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* ({@link org.apache.xml.dtm.DTM}) and previously established location
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* state.</p>
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* <p>Note that the original {@link CachedXPathAPI} and the new one should
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* not be operated upon concurrently; we do not support multithreaded access
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* to a single {@link org.apache.xml.dtm.DTM} at this time. Similarly,
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* any particular instance of {@link CachedXPathAPI} must not be operated
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* upon by multiple threads without synchronization.</p>
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* <p>%REVIEW% Should this instead do a clone-and-reset on the XPathSupport object?</p>
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*
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*/
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public CachedXPathAPI(CachedXPathAPI priorXPathAPI)
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{
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xpathSupport = priorXPathAPI.xpathSupport;
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}
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/** Returns the XPathSupport object used in this CachedXPathAPI
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*
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* %REVIEW% I'm somewhat concerned about the loss of encapsulation
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* this causes, but the xml-security folks say they need it.
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* */
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public XPathContext getXPathContext()
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{
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return this.xpathSupport;
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}
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/**
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* Use an XPath string to select a single node. XPath namespace
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* prefixes are resolved from the context node, which may not
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* be what you want (see the next method).
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*
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* @param contextNode The node to start searching from.
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* @param str A valid XPath string.
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* @return The first node found that matches the XPath, or null.
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*
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* @throws TransformerException
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*/
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public Node selectSingleNode(Node contextNode, String str)
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throws TransformerException
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{
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return selectSingleNode(contextNode, str, contextNode);
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}
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/**
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* Use an XPath string to select a single node.
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* XPath namespace prefixes are resolved from the namespaceNode.
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*
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* @param contextNode The node to start searching from.
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* @param str A valid XPath string.
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* @param namespaceNode The node from which prefixes in the XPath will be resolved to namespaces.
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* @return The first node found that matches the XPath, or null.
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*
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* @throws TransformerException
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*/
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public Node selectSingleNode(
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Node contextNode, String str, Node namespaceNode)
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throws TransformerException
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{
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// Have the XObject return its result as a NodeSetDTM.
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NodeIterator nl = selectNodeIterator(contextNode, str, namespaceNode);
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// Return the first node, or null
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return nl.nextNode();
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}
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/**
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* Use an XPath string to select a nodelist.
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* XPath namespace prefixes are resolved from the contextNode.
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*
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* @param contextNode The node to start searching from.
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* @param str A valid XPath string.
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* @return A NodeIterator, should never be null.
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*
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* @throws TransformerException
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*/
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public NodeIterator selectNodeIterator(Node contextNode, String str)
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throws TransformerException
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{
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return selectNodeIterator(contextNode, str, contextNode);
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}
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/**
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* Use an XPath string to select a nodelist.
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* XPath namespace prefixes are resolved from the namespaceNode.
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*
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* @param contextNode The node to start searching from.
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* @param str A valid XPath string.
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* @param namespaceNode The node from which prefixes in the XPath will be resolved to namespaces.
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* @return A NodeIterator, should never be null.
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*
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* @throws TransformerException
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*/
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public NodeIterator selectNodeIterator(
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Node contextNode, String str, Node namespaceNode)
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throws TransformerException
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{
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// Execute the XPath, and have it return the result
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XObject list = eval(contextNode, str, namespaceNode);
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// Have the XObject return its result as a NodeSetDTM.
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return list.nodeset();
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}
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/**
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* Use an XPath string to select a nodelist.
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* XPath namespace prefixes are resolved from the contextNode.
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*
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* @param contextNode The node to start searching from.
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* @param str A valid XPath string.
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* @return A NodeIterator, should never be null.
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*
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* @throws TransformerException
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*/
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public NodeList selectNodeList(Node contextNode, String str)
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throws TransformerException
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{
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return selectNodeList(contextNode, str, contextNode);
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}
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/**
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* Use an XPath string to select a nodelist.
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* XPath namespace prefixes are resolved from the namespaceNode.
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*
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* @param contextNode The node to start searching from.
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* @param str A valid XPath string.
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* @param namespaceNode The node from which prefixes in the XPath will be resolved to namespaces.
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* @return A NodeIterator, should never be null.
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*
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* @throws TransformerException
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*/
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public NodeList selectNodeList(
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Node contextNode, String str, Node namespaceNode)
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throws TransformerException
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{
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// Execute the XPath, and have it return the result
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XObject list = eval(contextNode, str, namespaceNode);
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// Return a NodeList.
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return list.nodelist();
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}
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/**
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* Evaluate XPath string to an XObject. Using this method,
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* XPath namespace prefixes will be resolved from the namespaceNode.
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* @param contextNode The node to start searching from.
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* @param str A valid XPath string.
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* @return An XObject, which can be used to obtain a string, number, nodelist, etc, should never be null.
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* @see org.apache.xpath.objects.XObject
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* @see org.apache.xpath.objects.XNull
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* @see org.apache.xpath.objects.XBoolean
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* @see org.apache.xpath.objects.XNumber
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* @see org.apache.xpath.objects.XString
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* @see org.apache.xpath.objects.XRTreeFrag
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*
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* @throws TransformerException
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*/
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public XObject eval(Node contextNode, String str)
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throws TransformerException
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{
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return eval(contextNode, str, contextNode);
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}
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/**
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* Evaluate XPath string to an XObject.
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* XPath namespace prefixes are resolved from the namespaceNode.
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* The implementation of this is a little slow, since it creates
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* a number of objects each time it is called. This could be optimized
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* to keep the same objects around, but then thread-safety issues would arise.
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*
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* @param contextNode The node to start searching from.
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* @param str A valid XPath string.
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* @param namespaceNode The node from which prefixes in the XPath will be resolved to namespaces.
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* @return An XObject, which can be used to obtain a string, number, nodelist, etc, should never be null.
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* @see org.apache.xpath.objects.XObject
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* @see org.apache.xpath.objects.XNull
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* @see org.apache.xpath.objects.XBoolean
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* @see org.apache.xpath.objects.XNumber
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* @see org.apache.xpath.objects.XString
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* @see org.apache.xpath.objects.XRTreeFrag
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*
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* @throws TransformerException
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*/
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public XObject eval(Node contextNode, String str, Node namespaceNode)
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throws TransformerException
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{
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// Since we don't have a XML Parser involved here, install some default support
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// for things like namespaces, etc.
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// (Changed from: XPathContext xpathSupport = new XPathContext();
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// because XPathContext is weak in a number of areas... perhaps
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// XPathContext should be done away with.)
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// Create an object to resolve namespace prefixes.
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// XPath namespaces are resolved from the input context node's document element
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// if it is a root node, or else the current context node (for lack of a better
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// resolution space, given the simplicity of this sample code).
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PrefixResolverDefault prefixResolver = new PrefixResolverDefault(
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(namespaceNode.getNodeType() == Node.DOCUMENT_NODE)
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? ((Document) namespaceNode).getDocumentElement() : namespaceNode);
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// Create the XPath object.
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XPath xpath = new XPath(str, null, prefixResolver, XPath.SELECT, null);
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// Execute the XPath, and have it return the result
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// return xpath.execute(xpathSupport, contextNode, prefixResolver);
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int ctxtNode = xpathSupport.getDTMHandleFromNode(contextNode);
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return xpath.execute(xpathSupport, ctxtNode, prefixResolver);
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}
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/**
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* Evaluate XPath string to an XObject.
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* XPath namespace prefixes are resolved from the namespaceNode.
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* The implementation of this is a little slow, since it creates
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* a number of objects each time it is called. This could be optimized
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* to keep the same objects around, but then thread-safety issues would arise.
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*
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* @param contextNode The node to start searching from.
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* @param str A valid XPath string.
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* @param prefixResolver Will be called if the parser encounters namespace
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* prefixes, to resolve the prefixes to URLs.
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* @return An XObject, which can be used to obtain a string, number, nodelist, etc, should never be null.
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* @see org.apache.xpath.objects.XObject
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* @see org.apache.xpath.objects.XNull
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* @see org.apache.xpath.objects.XBoolean
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* @see org.apache.xpath.objects.XNumber
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* @see org.apache.xpath.objects.XString
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* @see org.apache.xpath.objects.XRTreeFrag
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*
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* @throws TransformerException
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*/
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public XObject eval(
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Node contextNode, String str, PrefixResolver prefixResolver)
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throws TransformerException
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{
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|
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// Since we don't have a XML Parser involved here, install some default support
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// for things like namespaces, etc.
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// (Changed from: XPathContext xpathSupport = new XPathContext();
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// because XPathContext is weak in a number of areas... perhaps
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// XPathContext should be done away with.)
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// Create the XPath object.
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XPath xpath = new XPath(str, null, prefixResolver, XPath.SELECT, null);
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// Create an XPathContext that doesn't support pushing and popping of
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// variable resolution scopes. Sufficient for simple XPath 1.0 expressions.
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XPathContext xpathSupport = new XPathContext(false);
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// Execute the XPath, and have it return the result
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int ctxtNode = xpathSupport.getDTMHandleFromNode(contextNode);
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return xpath.execute(xpathSupport, ctxtNode, prefixResolver);
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}
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}
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