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