📄 buzzinservlet.java
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/* * Copyright (c) Ian F. Darwin, ian@darwinsys.com, 1996-2002. * All rights reserved. Software written by Ian F. Darwin and others. * $Id: BuzzInServlet.java,v 1.13 2002/07/01 13:45:51 ian Exp $ * * 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. All advertising materials mentioning features or use of this software * must display the following acknowledgement: * This product includes software developed by Ian F. Darwin. * 4. Neither the name of the author nor the names of its * contributors may be used to endorse or promote products derived * from this software without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' * AND ANY EXPRESS 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 AUTHOR OR 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. * * Java, the Duke mascot, and all variants of Sun's Java "steaming coffee * cup" logo are trademarks of Sun Microsystems. Sun's, and James Gosling's, * pioneering role in inventing and promulgating (and standardizing) the Java * language and environment is gratefully acknowledged. * * The pioneering role of Dennis Ritchie and Bjarne Stroustrup, of AT&T, for * inventing predecessor languages C and C++ is also gratefully acknowledged. */import javax.servlet.*;import javax.servlet.http.*;import java.io.*;/** A quiz-show "buzzer" servlet: the first respondant wins the chance * to answer the skill-testing question. * <p> * Previous versions of this code used shared static variables, but this * is not reliable, since most web engines now use custom class loaders * that may load a servlet class more than once. The "right" way is to * synchronize on an object stored in the Servlet Application Context. */public class BuzzInServlet extends HttpServlet { /** The attribute name used throughout. */ protected final static String WINNER = "buzzin.winner"; /** doGet is called from the contestants web page. * Uses a synchronized code block to ensure that * only one contestant can change the state of "buzzed". */ public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { ServletContext application = getServletContext(); boolean iWon = false; String user = request.getRemoteHost() + '@' + request.getRemoteAddr(); // Do the synchronized stuff first, and all in one place. synchronized(application) { if (application.getAttribute(WINNER) == null) { application.setAttribute(WINNER, user); application.log("BuzzInServlet: WINNER " + user); iWon = true; } } response.setContentType("text/html"); PrintWriter out = response.getWriter(); out.println("<html><head><title>Thanks for playing</title></head>"); out.println("<body bgcolor=\"white\">"); if (iWon) { out.println("<b>YOU GOT IT</b>"); // TODO - output HTML to play a sound file :-) } else { out.println("Thanks for playing, " + request.getRemoteAddr()); out.println(", but " + application.getAttribute(WINNER) + " buzzed in first"); } out.println("</body></html>"); } /** The Post method is used from an Administrator page (which should * only be installed in the instructor/host's localweb directory). * Post is used for administrative functions: * 1) to display the winner; * 2) to reset the buzzer for the next question. */ public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { ServletContext application = getServletContext(); response.setContentType("text/html"); HttpSession session = request.getSession(); PrintWriter out = response.getWriter(); if (request.isUserInRole("host")) { out.println("<html><head><title>Welcome back, " + request.getUserPrincipal().getName() + "</title><head>"); out.println("<body bgcolor=\"white\">"); String command = request.getParameter("command"); if (command.equals("reset")) { // Synchronize what you need, no more, no less. synchronized(application) { application.setAttribute(WINNER, null); } session.setAttribute("buzzin.message", "RESET"); } else if (command.equals("show")) { String winner = null; synchronized(application) { winner = (String)application.getAttribute(WINNER); } if (winner == null) { session.setAttribute("buzzin.message", "<b>No winner yet!</b>"); } else { session.setAttribute("buzzin.message", "<b>Winner is: </b>" + winner); } } else { session.setAttribute("buzzin.message", "ERROR: Command " + command + " invalid."); } RequestDispatcher rd = application.getRequestDispatcher( "/hosts/index.jsp"); rd.forward(request, response); } else { out.println("<html><head><title>Nice try, but... </title><head>"); out.println("<body bgcolor=\"white\">"); out.println( "I'm sorry, Dave, but you know I can't allow you to do that."); out.println("Even if you are " + request.getUserPrincipal()); } out.println("</body></html>"); }}⌨️ 快捷键说明
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