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    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   }

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