internal/domapi/XPathEvaluatorImpl.java

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 * reserved comment block
 * DO NOT REMOVE OR ALTER!
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/*
 * Copyright 2002-2005 The Apache Software Foundation.
 *
 * Licensed 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: XPathEvaluatorImpl.java,v 1.2.4.1 2005/09/10 04:04:07 jeffsuttor Exp $
 */

package com.sun.org.apache.xpath.internal.domapi;

import javax.xml.transform.TransformerException;

import com.sun.org.apache.xml.internal.utils.PrefixResolver;
import com.sun.org.apache.xpath.internal.XPath;
import com.sun.org.apache.xpath.internal.res.XPATHErrorResources;
import com.sun.org.apache.xpath.internal.res.XPATHMessages;
import org.w3c.dom.DOMException;
import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.w3c.dom.xpath.XPathEvaluator;
import org.w3c.dom.xpath.XPathException;
import org.w3c.dom.xpath.XPathExpression;
import org.w3c.dom.xpath.XPathNSResolver;

/**
 *
 * The class provides an implementation of XPathEvaluator according
 * to the DOM L3 XPath Specification, Working Group Note 26 February 2004.
 *
 * <p>See also the <a href='http://www.w3.org/TR/2004/NOTE-DOM-Level-3-XPath-20040226'>Document Object Model (DOM) Level 3 XPath Specification</a>.</p>
 *
 * </p>The evaluation of XPath expressions is provided by
 * <code>XPathEvaluator</code>, which will provide evaluation of XPath 1.0
 * expressions with no specialized extension functions or variables. It is
 * expected that the <code>XPathEvaluator</code> interface will be
 * implemented on the same object which implements the <code>Document</code>
 * interface in an implementation which supports the XPath DOM module.
 * <code>XPathEvaluator</code> implementations may be available from other
 * sources that may provide support for special extension functions or
 * variables which are not defined in this specification.</p>
 *
 * @see org.w3c.dom.xpath.XPathEvaluator
 *
 * @xsl.usage internal
 */
public final 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.
         */
        private class DummyPrefixResolver implements PrefixResolver {

                /**
                 * Constructor for DummyPrefixResolver.
                 */
                DummyPrefixResolver() {}

                /**
                 * @exception DOMException
         *   NAMESPACE_ERR: Always throws this exceptionn
                 *
                 * @see com.sun.org.apache.xml.internal.utils.PrefixResolver#getNamespaceForPrefix(String, Node)
                 */
                public String getNamespaceForPrefix(String prefix, Node context) {
            String fmsg = XPATHMessages.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 com.sun.org.apache.xml.internal.utils.PrefixResolver#getNamespaceForPrefix(String)
                 */
                public String getNamespaceForPrefix(String prefix) {
                        return getNamespaceForPrefix(prefix,null);
                }

                /**
                 * @see com.sun.org.apache.xml.internal.utils.PrefixResolver#handlesNullPrefixes()
                 */
                public boolean handlesNullPrefixes() {
                        return false;
                }

                /**
                 * @see com.sun.org.apache.xml.internal.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 final Document m_doc;

    /**
     * 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;
    }

    /**
     * Constructor in the case that the XPath expression can be evaluated
     * without needing an XML document at all.
     *
     */
    public XPathEvaluatorImpl() {
            m_doc = null;
    }

        /**
     * 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 <code>resolver</code> permits translation of
     *   prefixes within the XPath expression into appropriate namespace URIs
     *   . If this is specified as <code>null</code>, any namespace prefix
     *   within the expression will result in <code>DOMException</code>
     *   being thrown with the code <code>NAMESPACE_ERR</code>.
     * @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 <code>XPathEvaluator</code>i
     * @exception DOMException
     *   NAMESPACE_ERR: Raised if the expression contains namespace prefixes
     *   which cannot be resolved by the specified
     *   <code>XPathNSResolver</code>.
     *
         * @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) {
                        // Need to pass back exception code DOMException.NAMESPACE_ERR also.
                        // Error found in DOM Level 3 XPath Test Suite.
                        if(e instanceof XPathStylesheetDOM3Exception)
                                throw new DOMException(DOMException.NAMESPACE_ERR,e.getMessageAndLocation());
                        else
                                throw new XPathException(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 <code>lookupNamespaceURI</code> 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 <code>XPathNSResolver</code> 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 <code>context</code> is context node for the
     *   evaluation of this XPath expression. If the XPathEvaluator was
     *   obtained by casting the <code>Document</code> then this must be
     *   owned by the same document and must be a <code>Document</code>,
     *   <code>Element</code>, <code>Attribute</code>, <code>Text</code>,
     *   <code>CDATASection</code>, <code>Comment</code>,
     *   <code>ProcessingInstruction</code>, or <code>XPathNamespace</code>
     *   node. If the context node is a <code>Text</code> or a
     *   <code>CDATASection</code>, 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 <code>resolver</code> permits translation of
     *   prefixes within the XPath expression into appropriate namespace URIs
     *   . If this is specified as <code>null</code>, any namespace prefix
     *   within the expression will result in <code>DOMException</code>
     *   being thrown with the code <code>NAMESPACE_ERR</code>.
     * @param type If a specific <code>type</code> 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
     *   <code>XPathResult</code>.
     * @param result The <code>result</code> specifies a specific result
     *   object which may be reused and returned by this method. If this is
     *   specified as <code>null</code>or 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
     *   <code>XPathResult</code>.
     * @return The result of the evaluation of the XPath expression.For XPath
     *   1.0 results, this object will be of type <code>XPathResult</code>.
     * @exception XPathException
     *   INVALID_EXPRESSION_ERR: Raised if the expression is not legal
     *   according to the rules of the <code>XPathEvaluator</code>i
     *   <br>TYPE_ERR: Raised if the result cannot be converted to return the
     *   specified type.
     * @exception DOMException
     *   NAMESPACE_ERR: Raised if the expression contains namespace prefixes
     *   which cannot be resolved by the specified
     *   <code>XPathNSResolver</code>.
     *   <br>WRONG_DOCUMENT_ERR: The Node is from a document that is not
     *   supported by this XPathEvaluator.
     *   <br>NOT_SUPPORTED_ERR: The Node is not a type permitted as an XPath
     *   context node.
         *
         * @see org.w3c.dom.xpath.XPathEvaluator#evaluate(String, Node, XPathNSResolver, short, XPathResult)
         */
        public Object evaluate(
                String expression,
                Node contextNode,
                XPathNSResolver resolver,
                short type,
                Object result)
                throws XPathException, DOMException {

                XPathExpression xpathExpression = createExpression(expression, resolver);

                return  xpathExpression.evaluate(contextNode, type, result);
        }

}