/** Copyright 2004 The Apache Software Foundation** Licensed under the Apache License, Version 2.0 (the "License");* you may not use this file except in compliance with the License.* You may obtain a copy of the License at**     http://www.apache.org/licenses/LICENSE-2.0** Unless required by applicable law or agreed to in writing, software* distributed under the License is distributed on an "AS IS" BASIS,* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.* See the License for the specific language governing permissions and* limitations under the License.*/package javax.servlet;import java.io.IOException;import java.util.Enumeration;/** * * Defines a generic, protocol-independent * servlet. To write an HTTP servlet for use on the * Web, extend {@link javax.servlet.http.HttpServlet} instead. * * <p><code>GenericServlet</code> implements the <code>Servlet</code> * and <code>ServletConfig</code> interfaces. <code>GenericServlet</code> * may be directly extended by a servlet, although it's more common to extend * a protocol-specific subclass such as <code>HttpServlet</code>. * * <p><code>GenericServlet</code> makes writing servlets * easier. It provides simple versions of the lifecycle methods  * <code>init</code> and <code>destroy</code> and of the methods  * in the <code>ServletConfig</code> interface. <code>GenericServlet</code> * also implements the <code>log</code> method, declared in the * <code>ServletContext</code> interface.  * * <p>To write a generic servlet, you need only * override the abstract <code>service</code> method.  * * * @author 	Various * @version 	$Version$ * * * */ public abstract class GenericServlet     implements Servlet, ServletConfig, java.io.Serializable{    private transient ServletConfig config;        /**     *     * Does nothing. All of the servlet initialization     * is done by one of the <code>init</code> methods.     *     */    public GenericServlet() { }               /**     * Called by the servlet container to indicate to a servlet that the     * servlet is being taken out of service.  See {@link Servlet#destroy}.     *     *      */    public void destroy() {    }                /**     * Returns a <code>String</code> containing the value of the named     * initialization parameter, or <code>null</code> if the parameter does     * not exist.  See {@link ServletConfig#getInitParameter}.     *     * <p>This method is supplied for convenience. It gets the      * value of the named parameter from the servlet's      * <code>ServletConfig</code> object.     *     * @param name 		a <code>String</code> specifying the name      *				of the initialization parameter     *     * @return String 		a <code>String</code> containing the value     *				of the initialization parameter     *     */     public String getInitParameter(String name) {	return getServletConfig().getInitParameter(name);    }           /**    * Returns the names of the servlet's initialization parameters     * as an <code>Enumeration</code> of <code>String</code> objects,    * or an empty <code>Enumeration</code> if the servlet has no    * initialization parameters.  See {@link    * ServletConfig#getInitParameterNames}.    *    * <p>This method is supplied for convenience. It gets the     * parameter names from the servlet's <code>ServletConfig</code> object.     *    *    * @return Enumeration 	an enumeration of <code>String</code>    *				objects containing the names of     *				the servlet's initialization parameters    *    */    public Enumeration getInitParameterNames() {	return getServletConfig().getInitParameterNames();    }                      /**     * Returns this servlet's {@link ServletConfig} object.     *     * @return ServletConfig 	the <code>ServletConfig</code> object     *				that initialized this servlet     *     */        public ServletConfig getServletConfig() {	return config;    }                 /**     * Returns a reference to the {@link ServletContext} in which this servlet     * is running.  See {@link ServletConfig#getServletContext}.     *     * <p>This method is supplied for convenience. It gets the      * context from the servlet's <code>ServletConfig</code> object.     *     *     * @return ServletContext 	the <code>ServletContext</code> object     *				passed to this servlet by the <code>init</code>     *				method     *     */    public ServletContext getServletContext() {	return getServletConfig().getServletContext();    }     /**     * Returns information about the servlet, such as      * author, version, and copyright.      * By default, this method returns an empty string.  Override this method     * to have it return a meaningful value.  See {@link     * Servlet#getServletInfo}.     *     *     * @return String 		information about this servlet, by default an     * 				empty string     *     */        public String getServletInfo() {	return "";    }    /**     *     * Called by the servlet container to indicate to a servlet that the     * servlet is being placed into service.  See {@link Servlet#init}.     *     * <p>This implementation stores the {@link ServletConfig}     * object it receives from the servlet container for later use.     * When overriding this form of the method, call      * <code>super.init(config)</code>.     *     * @param config 			the <code>ServletConfig</code> object     *					that contains configutation     *					information for this servlet     *     * @exception ServletException 	if an exception occurs that     *					interrupts the servlet's normal     *					operation     *     *      * @see 				UnavailableException     *     */    public void init(ServletConfig config) throws ServletException {	this.config = config;	this.init();    }    /**     *     * A convenience method which can be overridden so that there's no need     * to call <code>super.init(config)</code>.     *     * <p>Instead of overriding {@link #init(ServletConfig)}, simply override     * this method and it will be called by     * <code>GenericServlet.init(ServletConfig config)</code>.     * The <code>ServletConfig</code> object can still be retrieved via {@link     * #getServletConfig}.      *     * @exception ServletException 	if an exception occurs that     *					interrupts the servlet's     *					normal operation     *     */        public void init() throws ServletException {    }        /**     *      * Writes the specified message to a servlet log file, prepended by the     * servlet's name.  See {@link ServletContext#log(String)}.     *     * @param msg 	a <code>String</code> specifying     *			the message to be written to the log file     *     */         public void log(String msg) {	getServletContext().log(getServletName() + ": "+ msg);    }                /**     * Writes an explanatory message and a stack trace     * for a given <code>Throwable</code> exception     * to the servlet log file, prepended by the servlet's name.     * See {@link ServletContext#log(String, Throwable)}.     *     *     * @param message 		a <code>String</code> that describes     *				the error or exception     *     * @param t			the <code>java.lang.Throwable</code> error     * 				or exception     *     *     */       public void log(String message, Throwable t) {	getServletContext().log(getServletName() + ": " + message, t);    }                /**     * Called by the servlet container to allow the servlet to respond to     * a request.  See {@link Servlet#service}.     *      * <p>This method is declared abstract so subclasses, such as      * <code>HttpServlet</code>, must override it.     *     *     *     * @param req 	the <code>ServletRequest</code> object     *			that contains the client's request     *     * @param res 	the <code>ServletResponse</code> object     *			that will contain the servlet's response     *     * @exception ServletException 	if an exception occurs that     *					interferes with the servlet's     *					normal operation occurred     *     * @exception IOException 		if an input or output     *					exception occurs     *     */    public abstract void service(ServletRequest req, ServletResponse res)	throws ServletException, IOException;        /**     * Returns the name of this servlet instance.     * See {@link ServletConfig#getServletName}.     *     * @return          the name of this servlet instance     *     *     *     */    public String getServletName() {        return config.getServletName();    }}