PC World 2002 May/PCWorld_2002-05_cd.bin/Komunik/sambar/sambar51p.exe/lib/javaeng.jar/javax/servlet/GenericServlet.java

Java Source | 2001-10-22 | 11.4 KB | 376 lines

/*
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 1999 The Apache Software Foundation.  All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution, if
 *    any, must include the following acknowlegement:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowlegement may appear in the software itself,
 *    if and wherever such third-party acknowlegements normally appear.
 *
 * 4. The names "The Jakarta Project", "Tomcat", and "Apache Software
 *    Foundation" must not be used to endorse or promote products derived
 *    from this software without prior written permission. For written
 *    permission, please contact [e-mail].
 *
 * 5. Products derived from this software may not be called "Apache"
 *    nor may "Apache" appear in their names without prior written
 *    permission of the Apache Group.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 *
 * ====================================================================
 *
 * This source code implements specifications defined by the Java
 * Community Process. In order to remain compliant with the specification
 * DO NOT add / change / or delete method signatures!
 */

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() {
    log("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 initalization 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 alter 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;
    log("init");
    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) {
        ServletContext context = getServletContext();
        if (context==null)
            System.err.println("GenericServlet.log(pre-init): "+
                               getServletName()+": "+msg);
        else
            context.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();
    }
}