001 /* $Id: Rule.java 471661 2006-11-06 08:09:25Z skitching $
002 *
003 * Licensed to the Apache Software Foundation (ASF) under one or more
004 * contributor license agreements. See the NOTICE file distributed with
005 * this work for additional information regarding copyright ownership.
006 * The ASF licenses this file to You under the Apache License, Version 2.0
007 * (the "License"); you may not use this file except in compliance with
008 * the License. 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
019
020 package org.apache.commons.digester;
021
022
023 import org.xml.sax.Attributes;
024
025
026 /**
027 * Concrete implementations of this class implement actions to be taken when
028 * a corresponding nested pattern of XML elements has been matched.
029 * <p>
030 * Writing a custom Rule is considered perfectly normal when using Digester,
031 * and is encouraged whenever the default set of Rule classes don't meet your
032 * requirements; the digester framework can help process xml even when the
033 * built-in rules aren't quite what is needed. Creating a custom Rule is
034 * just as easy as subclassing javax.servlet.http.HttpServlet for webapps,
035 * or javax.swing.Action for GUI applications.
036 * <p>
037 * If a rule wishes to manipulate a digester stack (the default object stack,
038 * a named stack, or the parameter stack) then it should only ever push
039 * objects in the rule's begin method and always pop exactly the same
040 * number of objects off the stack during the rule's end method. Of course
041 * peeking at the objects on the stacks can be done from anywhere.
042 * <p>
043 * Rule objects should be stateless, ie they should not update any instance
044 * member during the parsing process. A rule instance that changes state
045 * will encounter problems if invoked in a "nested" manner; this can happen
046 * if the same instance is added to digester multiple times or if a
047 * wildcard pattern is used which can match both an element and a child of the
048 * same element. The digester object stack and named stacks should be used to
049 * store any state that a rule requires, making the rule class safe under all
050 * possible uses.
051 */
052
053 public abstract class Rule {
054
055
056 // ----------------------------------------------------------- Constructors
057
058
059 /**
060 * Constructor sets the associated Digester.
061 *
062 * @param digester The digester with which this rule is associated
063 * @deprecated The digester instance is now set in the {@link Digester#addRule} method. Use {@link #Rule()} instead.
064 */
065 public Rule(Digester digester) {
066
067 super();
068 setDigester(digester);
069
070 }
071
072 /**
073 * <p>Base constructor.
074 * Now the digester will be set when the rule is added.</p>
075 */
076 public Rule() {}
077
078
079 // ----------------------------------------------------- Instance Variables
080
081
082 /**
083 * The Digester with which this Rule is associated.
084 */
085 protected Digester digester = null;
086
087
088 /**
089 * The namespace URI for which this Rule is relevant, if any.
090 */
091 protected String namespaceURI = null;
092
093
094 // ------------------------------------------------------------- Properties
095
096
097 /**
098 * Return the Digester with which this Rule is associated.
099 */
100 public Digester getDigester() {
101
102 return (this.digester);
103
104 }
105
106 /**
107 * Set the <code>Digester</code> with which this <code>Rule</code> is associated.
108 */
109 public void setDigester(Digester digester) {
110
111 this.digester = digester;
112
113 }
114
115 /**
116 * Return the namespace URI for which this Rule is relevant, if any.
117 */
118 public String getNamespaceURI() {
119
120 return (this.namespaceURI);
121
122 }
123
124
125 /**
126 * Set the namespace URI for which this Rule is relevant, if any.
127 *
128 * @param namespaceURI Namespace URI for which this Rule is relevant,
129 * or <code>null</code> to match independent of namespace.
130 */
131 public void setNamespaceURI(String namespaceURI) {
132
133 this.namespaceURI = namespaceURI;
134
135 }
136
137
138 // --------------------------------------------------------- Public Methods
139
140
141 /**
142 * This method is called when the beginning of a matching XML element
143 * is encountered.
144 *
145 * @param attributes The attribute list of this element
146 * @deprecated Use the {@link #begin(String,String,Attributes) begin}
147 * method with <code>namespace</code> and <code>name</code>
148 * parameters instead.
149 */
150 public void begin(Attributes attributes) throws Exception {
151
152 ; // The default implementation does nothing
153
154 }
155
156
157 /**
158 * This method is called when the beginning of a matching XML element
159 * is encountered. The default implementation delegates to the deprecated
160 * method {@link #begin(Attributes) begin} without the
161 * <code>namespace</code> and <code>name</code> parameters, to retain
162 * backwards compatibility.
163 *
164 * @param namespace the namespace URI of the matching element, or an
165 * empty string if the parser is not namespace aware or the element has
166 * no namespace
167 * @param name the local name if the parser is namespace aware, or just
168 * the element name otherwise
169 * @param attributes The attribute list of this element
170 * @since Digester 1.4
171 */
172 public void begin(String namespace, String name, Attributes attributes)
173 throws Exception {
174
175 begin(attributes);
176
177 }
178
179
180 /**
181 * This method is called when the body of a matching XML element
182 * is encountered. If the element has no body, this method is
183 * called with an empty string as the body text.
184 *
185 * @param text The text of the body of this element
186 * @deprecated Use the {@link #body(String,String,String) body} method
187 * with <code>namespace</code> and <code>name</code> parameters
188 * instead.
189 */
190 public void body(String text) throws Exception {
191
192 ; // The default implementation does nothing
193
194 }
195
196
197 /**
198 * This method is called when the body of a matching XML element is
199 * encountered. If the element has no body, this method is
200 * called with an empty string as the body text.
201 * <p>
202 * The default implementation delegates to the deprecated method
203 * {@link #body(String) body} without the <code>namespace</code> and
204 * <code>name</code> parameters, to retain backwards compatibility.
205 *
206 * @param namespace the namespace URI of the matching element, or an
207 * empty string if the parser is not namespace aware or the element has
208 * no namespace
209 * @param name the local name if the parser is namespace aware, or just
210 * the element name otherwise
211 * @param text The text of the body of this element
212 * @since Digester 1.4
213 */
214 public void body(String namespace, String name, String text)
215 throws Exception {
216
217 body(text);
218
219 }
220
221
222 /**
223 * This method is called when the end of a matching XML element
224 * is encountered.
225 *
226 * @deprecated Use the {@link #end(String,String) end} method with
227 * <code>namespace</code> and <code>name</code> parameters instead.
228 */
229 public void end() throws Exception {
230
231 ; // The default implementation does nothing
232
233 }
234
235
236 /**
237 * This method is called when the end of a matching XML element
238 * is encountered. The default implementation delegates to the deprecated
239 * method {@link #end end} without the
240 * <code>namespace</code> and <code>name</code> parameters, to retain
241 * backwards compatibility.
242 *
243 * @param namespace the namespace URI of the matching element, or an
244 * empty string if the parser is not namespace aware or the element has
245 * no namespace
246 * @param name the local name if the parser is namespace aware, or just
247 * the element name otherwise
248 * @since Digester 1.4
249 */
250 public void end(String namespace, String name)
251 throws Exception {
252
253 end();
254
255 }
256
257
258 /**
259 * This method is called after all parsing methods have been
260 * called, to allow Rules to remove temporary data.
261 */
262 public void finish() throws Exception {
263
264 ; // The default implementation does nothing
265
266 }
267
268
269 }