001    /*--------------------------------------------------------------------------+
002    $Id: XPathEvaluator.java 26700 2010-03-12 19:37:30Z hummelb $
003    |                                                                          |
004    | Copyright 2005-2010 Technische Universitaet Muenchen                     |
005    |                                                                          |
006    | Licensed under the Apache License, Version 2.0 (the "License");          |
007    | you may not use this file except in compliance with the License.         |
008    | You may obtain a copy of the License at                                  |
009    |                                                                          |
010    |    http://www.apache.org/licenses/LICENSE-2.0                            |
011    |                                                                          |
012    | Unless required by applicable law or agreed to in writing, software      |
013    | distributed under the License is distributed on an "AS IS" BASIS,        |
014    | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
015    | See the License for the specific language governing permissions and      |
016    | limitations under the License.                                           |
017    +--------------------------------------------------------------------------*/
018    package edu.tum.cs.commons.xml;
019    
020    import java.util.Iterator;
021    import java.util.List;
022    
023    import javax.xml.namespace.NamespaceContext;
024    import javax.xml.namespace.QName;
025    import javax.xml.xpath.XPath;
026    import javax.xml.xpath.XPathConstants;
027    import javax.xml.xpath.XPathExpressionException;
028    import javax.xml.xpath.XPathFactory;
029    
030    import org.w3c.dom.Element;
031    import org.w3c.dom.NodeList;
032    
033    import edu.tum.cs.commons.assertion.CCSMAssert;
034    import edu.tum.cs.commons.collections.BidirectionalMap;
035    
036    /**
037     * Evaluator for XPath expression. This is preferable to using the normal
038     * {@link XPath} class as it has built-in support for namespace-handling and the
039     * evaluation-method does not define exceptions.
040     * 
041     * @author deissenb
042     * @author $Author:deissenb $
043     * @version $Rev: 26700 $
044     * @levd.rating GREEN Hash: F642A48694AB2CF2F48DB533F005C740
045     */
046    public class XPathEvaluator {
047    
048            /** XPath object used to evaluate Bugzilla result document.s */
049            private final XPath xPath = XPathFactory.newInstance().newXPath();
050    
051            /** The namespace context to use. */
052            private final NSContext nsContext;
053    
054            /** Create new evaluator. */
055            public XPathEvaluator() {
056                    nsContext = new NSContext();
057                    xPath.setNamespaceContext(nsContext);
058            }
059    
060            /** Add a namespace. */
061            public void addNamespace(String prefix, String uri) {
062                    nsContext.addNamespace(prefix, uri);
063            }
064    
065            /**
066             * Evaluates an XPath expression on context element. This assumes that the
067             * XPath expression is valid and raises an {@link AssertionError} otherwise.
068             * 
069             * @param returnType
070             *            use {@link XPathConstants} to define return type.
071             */
072            public Object select(String expr, Element context, QName returnType) {
073                    try {
074                            return xPath.evaluate(expr, context, returnType);
075                    } catch (XPathExpressionException e) {
076                            CCSMAssert.fail(e.getMessage());
077                            return null;
078                    }
079            }
080    
081            /**
082             * Evaluates an XPath expression on context element. This assumes that the
083             * XPath expression is valid and raises an {@link AssertionError} otherwise.
084             */
085            public List<Element> selectList(String expr, Element context) {
086                    return XMLUtils.elementNodes(selectNodeList(expr, context));
087            }
088    
089            /**
090             * Evaluates an XPath expression on context element. This assumes that the
091             * XPath expression is valid and raises an {@link AssertionError} otherwise.
092             */
093            public NodeList selectNodeList(String expr, Element context) {
094                    return (NodeList) select(expr, context, XPathConstants.NODESET);
095            }
096    
097            /**
098             * Evaluates an XPath expression on context element. This assumes that the
099             * XPath expression is valid and raises an {@link AssertionError} otherwise.
100             */
101            public Element selectElement(String expr, Element context) {
102                    return (Element) select(expr, context, XPathConstants.NODE);
103            }
104    
105            /**
106             * Evaluates an XPath expression on context element. This assumes that the
107             * XPath expression is valid and raises an {@link AssertionError} otherwise.
108             */
109            public String selectString(String expr, Element context) {
110                    return (String) select(expr, context, XPathConstants.STRING);
111            }
112    
113            /**
114             * Evaluates an XPath expression on context element. This assumes that the
115             * XPath expression is valid and raises an {@link AssertionError} otherwise.
116             * Due to the implementation of {@link XPath} this returns 0.0 if the
117             * element was not found.
118             */
119            public double selectDouble(String expr, Element context) {
120                    return (Double) select(expr, context, XPathConstants.NUMBER);
121            }
122    
123            /**
124             * Evaluates an XPath expression on context element. This assumes that the
125             * XPath expression is valid and raises an {@link AssertionError} otherwise.
126             * Due to the implementation of {@link XPath} this returns 0 if the element
127             * was not found.
128             */
129            public int selectInt(String expr, Element context) {
130                    return ((Double) select(expr, context, XPathConstants.NUMBER))
131                                    .intValue();
132            }
133    
134            /**
135             * Evaluates an XPath expression on context element. This assumes that the
136             * XPath expression is valid and raises an {@link AssertionError} otherwise.
137             * Due to the implementation of {@link XPath} this returns
138             * <code>false</code> if the element was not found.
139             */
140            public boolean selectBoolean(String expr, Element context) {
141                    return (Boolean) select(expr, context, XPathConstants.BOOLEAN);
142            }
143    
144            /** Simple namespace context. */
145            private static class NSContext implements NamespaceContext {
146    
147                    /** Maps from prefix (first) to namespace URI (second). */
148                    private final BidirectionalMap<String, String> map = new BidirectionalMap<String, String>();
149    
150                    /** Add new namespace to both maps. */
151                    private void addNamespace(String prefix, String uri) {
152                            map.put(prefix, uri);
153                    }
154    
155                    /** {@inheritDoc} */
156                    public String getNamespaceURI(String prefix) {
157                            return map.getSecond(prefix);
158                    }
159    
160                    /** {@inheritDoc} */
161                    public String getPrefix(String namespaceURI) {
162                            return map.getFirst(namespaceURI);
163                    }
164    
165                    /** {@inheritDoc} */
166                    @SuppressWarnings("unchecked")
167                    public Iterator getPrefixes(String namespaceURI) {
168                            return map.getFirstSet().iterator();
169                    }
170            }
171    }