GenericServlet


1   /*
2   * Licensed to the Apache Software Foundation (ASF) under one or more
3   * contributor license agreements.  See the NOTICE file distributed with
4   * this work for additional information regarding copyright ownership.
5   * The ASF licenses this file to You under the Apache License, Version 2.0
6   * (the "License"); you may not use this file except in compliance with
7   * the License.  You may obtain a copy of the License at
8   *
9   *     http://www.apache.org/licenses/LICENSE-2.0
10  *
11  * Unless required by applicable law or agreed to in writing, software
12  * distributed under the License is distributed on an "AS IS" BASIS,
13  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14  * See the License for the specific language governing permissions and
15  * limitations under the License.
16  */
17  package javax.servlet;
18  
19  import java.io.IOException  ;
20  import java.util.Enumeration  ;
21  
22  /**
23   *
24   * Defines a generic, protocol-independent
25   * servlet. To write an HTTP servlet for use on the
26   * Web, extend {@link javax.servlet.http.HttpServlet} instead.
27   *
28   * <p><code>GenericServlet</code> implements the <code>Servlet</code>
29   * and <code>ServletConfig</code> interfaces. <code>GenericServlet</code>
30   * may be directly extended by a servlet, although it's more common to extend
31   * a protocol-specific subclass such as <code>HttpServlet</code>.
32   *
33   * <p><code>GenericServlet</code> makes writing servlets
34   * easier. It provides simple versions of the lifecycle methods 
35   * <code>init</code> and <code>destroy</code> and of the methods 
36   * in the <code>ServletConfig</code> interface. <code>GenericServlet</code>
37   * also implements the <code>log</code> method, declared in the
38   * <code>ServletContext</code> interface. 
39   *
40   * <p>To write a generic servlet, you need only
41   * override the abstract <code>service</code> method. 
42   *
43   *
44   * @author  Various
45   * @version     $Version$
46   *
47   *
48   *
49   */
50  
51   
52  public abstract class GenericServlet 
53      implements Servlet  , ServletConfig  , java.io.Serializable  
54  {
55  
56      private transient ServletConfig   config;
57      
58  
59      /**
60       *
61       * Does nothing. All of the servlet initialization
62       * is done by one of the <code>init</code> methods.
63       *
64       */
65  
66      public GenericServlet() { }
67      
68      
69      
70     /**
71       * Called by the servlet container to indicate to a servlet that the
72       * servlet is being taken out of service.  See {@link Servlet#destroy}.
73       *
74       * 
75       */
76  
77      public void destroy() {
78      }
79      
80      
81      
82      /**
83       * Returns a <code>String</code> containing the value of the named
84       * initialization parameter, or <code>null</code> if the parameter does
85       * not exist.  See {@link ServletConfig#getInitParameter}.
86       *
87       * <p>This method is supplied for convenience. It gets the 
88       * value of the named parameter from the servlet's 
89       * <code>ServletConfig</code> object.
90       *
91       * @param name      a <code>String</code> specifying the name 
92       *              of the initialization parameter
93       *
94       * @return String       a <code>String</code> containing the value
95       *              of the initialization parameter
96       *
97       */ 
98  
99      public String   getInitParameter(String   name) {
100     return getServletConfig().getInitParameter(name);
101     }
102     
103     
104 
105    /**
106     * Returns the names of the servlet's initialization parameters 
107     * as an <code>Enumeration</code> of <code>String</code> objects,
108     * or an empty <code>Enumeration</code> if the servlet has no
109     * initialization parameters.  See {@link
110     * ServletConfig#getInitParameterNames}.
111     *
112     * <p>This method is supplied for convenience. It gets the 
113     * parameter names from the servlet's <code>ServletConfig</code> object. 
114     *
115     *
116     * @return Enumeration   an enumeration of <code>String</code>
117     *               objects containing the names of 
118     *               the servlet's initialization parameters
119     *
120     */
121 
122     public Enumeration   getInitParameterNames() {
123     return getServletConfig().getInitParameterNames();
124     }   
125     
126      
127  
128      
129 
130     /**
131      * Returns this servlet's {@link ServletConfig} object.
132      *
133      * @return ServletConfig    the <code>ServletConfig</code> object
134      *              that initialized this servlet
135      *
136      */
137     
138     public ServletConfig   getServletConfig() {
139     return config;
140     }
141     
142     
143  
144     
145     /**
146      * Returns a reference to the {@link ServletContext} in which this servlet
147      * is running.  See {@link ServletConfig#getServletContext}.
148      *
149      * <p>This method is supplied for convenience. It gets the 
150      * context from the servlet's <code>ServletConfig</code> object.
151      *
152      *
153      * @return ServletContext   the <code>ServletContext</code> object
154      *              passed to this servlet by the <code>init</code>
155      *              method
156      *
157      */
158 
159     public ServletContext   getServletContext() {
160     return getServletConfig().getServletContext();
161     }
162 
163 
164 
165  
166 
167     /**
168      * Returns information about the servlet, such as 
169      * author, version, and copyright. 
170      * By default, this method returns an empty string.  Override this method
171      * to have it return a meaningful value.  See {@link
172      * Servlet#getServletInfo}.
173      *
174      *
175      * @return String       information about this servlet, by default an
176      *              empty string
177      *
178      */
179     
180     public String   getServletInfo() {
181     return "";
182     }
183 
184 
185 
186 
187     /**
188      *
189      * Called by the servlet container to indicate to a servlet that the
190      * servlet is being placed into service.  See {@link Servlet#init}.
191      *
192      * <p>This implementation stores the {@link ServletConfig}
193      * object it receives from the servlet container for later use.
194      * When overriding this form of the method, call 
195      * <code>super.init(config)</code>.
196      *
197      * @param config            the <code>ServletConfig</code> object
198      *                  that contains configutation
199      *                  information for this servlet
200      *
201      * @exception ServletException  if an exception occurs that
202      *                  interrupts the servlet's normal
203      *                  operation
204      *
205      * 
206      * @see                 UnavailableException
207      *
208      */
209 
210     public void init(ServletConfig   config) throws ServletException   {
211     this.config = config;
212     this.init();
213     }
214 
215 
216 
217 
218 
219     /**
220      *
221      * A convenience method which can be overridden so that there's no need
222      * to call <code>super.init(config)</code>.
223      *
224      * <p>Instead of overriding {@link #init(ServletConfig)}, simply override
225      * this method and it will be called by
226      * <code>GenericServlet.init(ServletConfig config)</code>.
227      * The <code>ServletConfig</code> object can still be retrieved via {@link
228      * #getServletConfig}. 
229      *
230      * @exception ServletException  if an exception occurs that
231      *                  interrupts the servlet's
232      *                  normal operation
233      *
234      */
235     
236     public void init() throws ServletException   {
237 
238     }
239     
240 
241 
242 
243     /**
244      * 
245      * Writes the specified message to a servlet log file, prepended by the
246      * servlet's name.  See {@link ServletContext#log(String)}.
247      *
248      * @param msg   a <code>String</code> specifying
249      *          the message to be written to the log file
250      *
251      */
252      
253     public void log(String   msg) {
254     getServletContext().log(getServletName() + ": "+ msg);
255     }
256    
257    
258    
259    
260     /**
261      * Writes an explanatory message and a stack trace
262      * for a given <code>Throwable</code> exception
263      * to the servlet log file, prepended by the servlet's name.
264      * See {@link ServletContext#log(String, Throwable)}.
265      *
266      *
267      * @param message       a <code>String</code> that describes
268      *              the error or exception
269      *
270      * @param t         the <code>java.lang.Throwable</code> error
271      *              or exception
272      *
273      *
274      */
275    
276     public void log(String   message, Throwable   t) {
277     getServletContext().log(getServletName() + ": " + message, t);
278     }
279     
280     
281     
282     /**
283      * Called by the servlet container to allow the servlet to respond to
284      * a request.  See {@link Servlet#service}.
285      * 
286      * <p>This method is declared abstract so subclasses, such as 
287      * <code>HttpServlet</code>, must override it.
288      *
289      *
290      *
291      * @param req   the <code>ServletRequest</code> object
292      *          that contains the client's request
293      *
294      * @param res   the <code>ServletResponse</code> object
295      *          that will contain the servlet's response
296      *
297      * @exception ServletException  if an exception occurs that
298      *                  interferes with the servlet's
299      *                  normal operation occurred
300      *
301      * @exception IOException       if an input or output
302      *                  exception occurs
303      *
304      */
305 
306     public abstract void service(ServletRequest   req, ServletResponse   res)
307     throws ServletException  , IOException  ;
308     
309 
310 
311     /**
312      * Returns the name of this servlet instance.
313      * See {@link ServletConfig#getServletName}.
314      *
315      * @return          the name of this servlet instance
316      *
317      *
318      *
319      */
320 
321     public String   getServletName() {
322         return config.getServletName();
323     }
324 }
325
A to Z: JavaDoc & Examples Daily Java News & Articles Open Source Projects Open Source Codes Free Computer Books Remove Frame
Popular Tags