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Java > Open Source Codes > org > apache > commons > jxpath > xml > DocumentContainer


1 /*
2  * Copyright 1999-2004 The Apache Software Foundation
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  * http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 package org.apache.commons.jxpath.xml;
17
18 import java.io.InputStream JavaDoc;
19 import java.net.URL JavaDoc;
20 import java.util.HashMap JavaDoc;
21
22 import org.apache.commons.jxpath.Container;
23 import org.apache.commons.jxpath.JXPathException;
24
25 /**
26  * An XML document container reads and parses XML only when it is
27  * accessed. JXPath traverses Containers transparently -
28  * you use the same paths to access objects in containers as you
29  * do to access those objects directly. You can create
30  * XMLDocumentContainers for various XML documents that may or
31  * may not be accessed by XPaths. If they are, they will be automatically
32  * read, parsed and traversed. If they are not - they won't be
33  * read at all.
34  *
35  * @author Dmitri Plotnikov
36  * @version $Revision: 1.9 $ $Date: 2004/02/29 14:17:37 $
37  */
38 public class DocumentContainer extends XMLParser2 implements Container {
39
40     public static final String JavaDoc MODEL_DOM = "DOM";
41     public static final String JavaDoc MODEL_JDOM = "JDOM";
42
43     private Object JavaDoc document;
44     private URL JavaDoc xmlURL;
45     private String JavaDoc model;
46
47     private static HashMap JavaDoc parserClasses = new HashMap JavaDoc();
48     static {
49         parserClasses.put(MODEL_DOM,
50                           "org.apache.commons.jxpath.xml.DOMParser");
51         parserClasses.put(MODEL_JDOM,
52                           "org.apache.commons.jxpath.xml.JDOMParser");
53     }
54
55     private static HashMap JavaDoc parsers = new HashMap JavaDoc();
56
57     /**
58      * Add an XML parser. Parsers for the models "DOM" and "JDOM" are
59      * pre-registered.
60      */
61     public static void registerXMLParser(String JavaDoc model, XMLParser parser) {
62         parsers.put(model, parser);
63     }
64
65     /**
66      * Add a class of a custom XML parser.
67      * Parsers for the models "DOM" and "JDOM" are pre-registered.
68      */
69     public static void registerXMLParser(String JavaDoc model, String JavaDoc parserClassName) {
70         parserClasses.put(model, parserClassName);
71     }
72
73     /**
74      * Use this constructor if the desired model is DOM.
75      *
76      * @param URL is a URL for an XML file.
77      * Use getClass().getResource(resourceName) to load XML from a
78      * resource file.
79      */
80     public DocumentContainer(URL JavaDoc xmlURL) {
81         this(xmlURL, MODEL_DOM);
82     }
83
84     /**
85      * @param URL is a URL for an XML file. Use getClass().getResource
86      * (resourceName) to load XML from a resource file.
87      *
88      * @param model is one of the MODEL_* constants defined in this class. It
89      * determines which parser should be used to load the XML.
90      */
91     public DocumentContainer(URL JavaDoc xmlURL, String JavaDoc model) {
92         this.xmlURL = xmlURL;
93         if (xmlURL == null) {
94             throw new JXPathException("XML URL is null");
95         }
96         this.model = model;
97     }
98
99     /**
100      * Reads XML, caches it internally and returns the Document.
101      */
102     public Object JavaDoc getValue() {
103         if (document == null) {
104             try {
105                 InputStream JavaDoc stream = null;
106                 try {
107                     if (xmlURL != null) {
108                         stream = xmlURL.openStream();
109                     }
110                     document = parseXML(stream);
111                 }
112                 finally {
113                     if (stream != null) {
114                         stream.close();
115                     }
116                 }
117             }
118             catch (Exception JavaDoc ex) {
119                 throw new JXPathException(
120                     "Cannot read XML from: " + xmlURL.toString(),
121                     ex);
122             }
123         }
124         return document;
125     }
126
127     /**
128      * Parses XML using the parser for the specified model.
129      */
130     public Object JavaDoc parseXML(InputStream JavaDoc stream) {
131         XMLParser parser = getParser(model);
132         if (parser instanceof XMLParser2) {
133             XMLParser2 parser2 = (XMLParser2) parser;
134             parser2.setValidating(isValidating());
135             parser2.setNamespaceAware(isNamespaceAware());
136             parser2.setIgnoringElementContentWhitespace(
137                     isIgnoringElementContentWhitespace());
138             parser2.setExpandEntityReferences(isExpandEntityReferences());
139             parser2.setIgnoringComments(isIgnoringComments());
140             parser2.setCoalescing(isCoalescing());
141         }
142         return parser.parseXML(stream);
143     }
144
145     /**
146      * Throws an UnsupportedOperationException
147      */
148     public void setValue(Object JavaDoc value) {
149         throw new UnsupportedOperationException JavaDoc();
150     }
151
152     /**
153      * Maps a model type to a parser.
154      */
155     private static final XMLParser getParser(String JavaDoc model) {
156         XMLParser parser = (XMLParser) parsers.get(model);
157         if (parser == null) {
158             String JavaDoc className = (String JavaDoc) parserClasses.get(model);
159             if (className == null) {
160                 throw new JXPathException("Unsupported XML model: " + model);
161             }
162             try {
163                 Class JavaDoc clazz = Class.forName(className);
164                 parser = (XMLParser) clazz.newInstance();
165             }
166             catch (Exception JavaDoc ex) {
167                 throw new JXPathException(
168                     "Cannot allocate XMLParser: " + className);
169             }
170             parsers.put(model, parser);
171         }
172         return parser;
173     }
174 }
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