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/*
 * Copyright (c) 1997-2018 Oracle and/or its affiliates. All rights reserved.
 * 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;
import java.util.ResourceBundle;


Defines a generic, protocol-independent servlet. To write an HTTP servlet for use on the Web, extend HttpServlet instead. 
GenericServlet implements the Servlet
and ServletConfig interfaces. GenericServlet
may be directly extended by a servlet, although it's more common to extend
a protocol-specific subclass such as HttpServlet.

GenericServlet makes writing servlets
easier. It provides simple versions of the lifecycle methods 
init and destroy and of the methods 
in the ServletConfig interface. GenericServlet
also implements the log method, declared in the
ServletContext interface. 

To write a generic servlet, you need only
override the abstract service method. 

Author:	Various
/**
 *
 * 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
 */

 
public abstract class GenericServlet 
    implements Servlet, ServletConfig, java.io.Serializable
{
    private static final String LSTRING_FILE = "javax.servlet.LocalStrings";
    private static ResourceBundle lStrings =
        ResourceBundle.getBundle(LSTRING_FILE);

    private transient ServletConfig config;
    

    
Does nothing. All of the servlet initialization
is done by one of the init methods.

/**
     *
     * 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 Servlet.destroy. 
/**
     * 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 String containing the value of the named
initialization parameter, or null if the parameter does not exist. See ServletConfig.getInitParameter. 
This method is supplied for convenience. It gets the 
value of the named parameter from the servlet's 
ServletConfig object.

Params:
  • name – 		a String specifying the name 
			of the initialization parameter
Returns:String 		a String containing the value
			of the initialization parameter
/**
     * 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) {
        ServletConfig sc = getServletConfig();
        if (sc == null) {
            throw new IllegalStateException(
                lStrings.getString("err.servlet_config_not_initialized"));
        }

        return sc.getInitParameter(name);
    }
    
    
   
Returns the names of the servlet's initialization parameters 
as an Enumeration of String objects,
or an empty Enumeration if the servlet has no initialization parameters. See ServletConfig.getInitParameterNames. 
This method is supplied for convenience. It gets the 
parameter names from the servlet's ServletConfig object. 

Returns:Enumeration 	an enumeration of String
			objects containing the names of 
			the servlet's initialization parameters
/**
    * 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<String> getInitParameterNames() {
        ServletConfig sc = getServletConfig();
        if (sc == null) {
            throw new IllegalStateException(
                lStrings.getString("err.servlet_config_not_initialized"));
        }

        return sc.getInitParameterNames();
    }   
     

    
Returns this servlet's ServletConfig object. 
Returns:ServletConfig 	the ServletConfig object
			that initialized this servlet
/**
     * 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 ServletContext in which this servlet is running. See ServletConfig.getServletContext. 
This method is supplied for convenience. It gets the 
context from the servlet's ServletConfig object.

Returns:ServletContext 	the ServletContext object
			passed to this servlet by the init
			method
/**
     * 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() {
        ServletConfig sc = getServletConfig();
        if (sc == null) {
            throw new IllegalStateException(
                lStrings.getString("err.servlet_config_not_initialized"));
        }

        return sc.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 Servlet.getServletInfo. 
Returns:String 		information about this servlet, by default an
				empty string
/**
     * 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 Servlet.init. 
This implementation stores the ServletConfig object it receives from the servlet container for later use. When overriding this form of the method, call super.init(config).

Params:
  • config – 			the ServletConfig object
				that contains configuration
				information for this servlet
Throws:
  • ServletException – 	if an exception occurs that
				interrupts the servlet's normal
				operation
See Also:
/**
     * 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 configuration
     *					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 super.init(config).

Instead of overriding init(ServletConfig), simply override this method and it will be called by GenericServlet.init(ServletConfig config).
The ServletConfig object can still be retrieved via getServletConfig. 
Throws:
  • ServletException – 	if an exception occurs that
				interrupts the servlet's
				normal operation
/**
     * 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 ServletContext.log(String). 
Params:
  • msg – 	a String specifying
		the message to be written to the log file
/**
     * 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 Throwable exception to the servlet log file, prepended by the servlet's name. See ServletContext.log(String, Throwable). 
Params:
  • message – 		a String that describes
			the error or exception
  • t – 			the java.lang.Throwable error
				or exception
/**
     * 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 Servlet.service. 
This method is declared abstract so subclasses, such as 
HttpServlet, must override it.

Params:
  • req – 	the ServletRequest object
		that contains the client's request
  • res – 	the ServletResponse object
		that will contain the servlet's response
Throws:
  • ServletException – 	if an exception occurs that
				interferes with the servlet's
				normal operation occurred
  • IOException – 		if an input or output
				exception occurs
/**
     * 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 ServletConfig.getServletName. 
Returns:         the name of this servlet instance
/**
     * Returns the name of this servlet instance.
     * See {@link ServletConfig#getServletName}.
     *
     * @return          the name of this servlet instance
     */
    public String getServletName() {
        ServletConfig sc = getServletConfig();
        if (sc == null) {
            throw new IllegalStateException(
                lStrings.getString("err.servlet_config_not_initialized"));
        }

        return sc.getServletName();
    }
}