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Java > Open Source Codes > org > jfree > xml > parser > AbstractXmlReadHandler


1 /* ========================================================================
2  * JCommon : a free general purpose class library for the Java(tm) platform
3  * ========================================================================
4  *
5  * (C) Copyright 2000-2005, by Object Refinery Limited and Contributors.
6  *
7  * Project Info: http://www.jfree.org/jcommon/index.html
8  *
9  * This library is free software; you can redistribute it and/or modify it
10  * under the terms of the GNU Lesser General Public License as published by
11  * the Free Software Foundation; either version 2.1 of the License, or
12  * (at your option) any later version.
13  *
14  * This library is distributed in the hope that it will be useful, but
15  * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
16  * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
17  * License for more details.
18  *
19  * You should have received a copy of the GNU Lesser General Public
20  * License along with this library; if not, write to the Free Software
21  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
22  * USA.
23  *
24  * [Java is a trademark or registered trademark of Sun Microsystems, Inc.
25  * in the United States and other countries.]
26  *
27  * ---------------------------
28  * AbstractXmlReadHandler.java
29  * ---------------------------
30  * (C)opyright 2003, 2004, by Thomas Morgner and Contributors.
31  *
32  * Original Author: Thomas Morgner;
33  * Contributor(s): David Gilbert (for Object Refinery Limited);
34  *
35  * $Id: AbstractXmlReadHandler.java,v 1.4 2005/10/18 13:32:52 mungady Exp $
36  *
37  * Changes (from 25-Nov-2003)
38  * --------------------------
39  * 25-Nov-2003 : Added Javadocs (DG);
40  *
41  */
42 package org.jfree.xml.parser;
43
44 import org.xml.sax.Attributes JavaDoc;
45 import org.xml.sax.SAXException JavaDoc;
46 import org.jfree.util.Log;
47
48 /**
49  * A base class for implementing an {@link XmlReadHandler}.
50  */
51 public abstract class AbstractXmlReadHandler implements XmlReadHandler {
52     /** The root handler. */
53     private RootXmlReadHandler rootHandler;
54
55     /** The tag name. */
56     private String JavaDoc tagName;
57
58     /** A flag indicating the first call. */
59     private boolean firstCall = true;
60
61     /**
62      * Creates a new handler.
63      */
64     public AbstractXmlReadHandler() {
65     }
66
67     /**
68      * Initialises the handler.
69      *
70      * @param rootHandler the root handler.
71      * @param tagName the tag name.
72      */
73     public void init(final RootXmlReadHandler rootHandler, final String JavaDoc tagName) {
74         if (rootHandler == null) {
75             throw new NullPointerException JavaDoc("Root handler must not be null");
76         }
77         if (tagName == null) {
78             throw new NullPointerException JavaDoc("Tag name must not be null");
79         }
80         this.rootHandler = rootHandler;
81         this.tagName = tagName;
82     }
83
84     /**
85      * This method is called at the start of an element.
86      *
87      * @param tagName the tag name.
88      * @param attrs the attributes.
89      *
90      * @throws SAXException if there is a parsing error.
91      * @throws XmlReaderException if there is a reader error.
92      */
93     public final void startElement(final String JavaDoc tagName, final Attributes JavaDoc attrs)
94         throws XmlReaderException, SAXException JavaDoc {
95         if (this.firstCall) {
96             if (!this.tagName.equals(tagName)) {
97                 throw new SAXException JavaDoc("Expected <" + this.tagName + ">, found <" + tagName + ">");
98             }
99             this.firstCall = false;
100             startParsing(attrs);
101         }
102         else {
103             final XmlReadHandler childHandler = getHandlerForChild(tagName, attrs);
104             if (childHandler == null) {
105                 Log.warn ("Unknown tag <" + tagName + ">");
106                 return;
107             }
108             childHandler.init(getRootHandler(), tagName);
109             this.rootHandler.recurse(childHandler, tagName, attrs);
110         }
111     }
112
113     /**
114      * This method is called to process the character data between element tags.
115      *
116      * @param ch the character buffer.
117      * @param start the start index.
118      * @param length the length.
119      *
120      * @throws SAXException if there is a parsing error.
121      */
122     public void characters(final char[] ch, final int start, final int length) throws SAXException JavaDoc {
123         // nothing required
124 }
125
126     /**
127      * This method is called at the end of an element.
128      *
129      * @param tagName the tag name.
130      *
131      * @throws SAXException if there is a parsing error.
132      */
133     public final void endElement(final String JavaDoc tagName) throws SAXException JavaDoc {
134         if (this.tagName.equals(tagName)) {
135             try {
136                 doneParsing();
137                 this.rootHandler.unwind(tagName);
138             }
139             catch (XmlReaderException xre) {
140                 throw new SAXException JavaDoc(xre);
141             }
142         }
143     }
144
145     /**
146      * Starts parsing.
147      *
148      * @param attrs the attributes.
149      *
150      * @throws SAXException if there is a parsing error.
151      */
152     protected void startParsing(final Attributes JavaDoc attrs) throws SAXException JavaDoc, XmlReaderException {
153         // nothing required
154 }
155
156     /**
157      * Done parsing.
158      *
159      * @throws SAXException if there is a parsing error.
160      * @throws XmlReaderException if there is a reader error.
161      */
162     protected void doneParsing() throws SAXException JavaDoc, XmlReaderException {
163         // nothing required
164 }
165
166     /**
167      * Returns the handler for a child element.
168      *
169      * @param tagName the tag name.
170      * @param atts the attributes.
171      *
172      * @return the handler or null, if the tagname is invalid.
173      *
174      * @throws SAXException if there is a parsing error.
175      * @throws XmlReaderException if there is a reader error.
176      */
177     protected XmlReadHandler getHandlerForChild(final String JavaDoc tagName, final Attributes JavaDoc atts)
178         throws XmlReaderException, SAXException JavaDoc {
179         return null;
180     }
181
182     /**
183      * Returns the tag name.
184      *
185      * @return the tag name.
186      */
187     public String JavaDoc getTagName() {
188         return this.tagName;
189     }
190
191     /**
192      * Returns the root handler for the parsing.
193      *
194      * @return the root handler.
195      */
196     public RootXmlReadHandler getRootHandler() {
197         return this.rootHandler;
198     }
199     
200 }
201
202
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