https://tomcat.apache.org/: jakarta.servlet package 
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 * (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
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 * distributed under the License is distributed on an "AS IS" BASIS,
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 * See the License for the specific language governing permissions and
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package jakarta.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 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.

/**
 * Defines a generic, protocol-independent servlet. To write an HTTP servlet for
 * use on the Web, extend {@link jakarta.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.
 */
public abstract class GenericServlet implements Servlet, ServletConfig,
        java.io.Serializable {

    private static final long serialVersionUID = 1L;

    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() {
        // NOOP
    }

    
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}.
     */
    @Override
    public void destroy() {
        // NOOP by default
    }

    
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
     */
    @Override
    public String getInitParameter(String name) {
        return getServletConfig().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
     */
    @Override
    public Enumeration<String> getInitParameterNames() {
        return getServletConfig().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
     */
    @Override
    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
     */
    @Override
    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 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
     */
    @Override
    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
     */
    @Override
    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 {
        // NOOP by default
    }

    
Writes the specified message to a servlet log file, prepended by the servlet's name. See ServletContext.log(String). 
Params:
  • message – 
           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 message
     *            a <code>String</code> specifying the message to be written to
     *            the log file
     */
    public void log(String message) {
        getServletContext().log(getServletName() + ": " + message);
    }

    
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
     */
    @Override
    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
     */
    @Override
    public String getServletName() {
        return config.getServletName();
    }
}