package buzzin;
/*
* Copyright (c) Ian F. Darwin, http://www.darwinsys.com/, 1996-2002.
* All rights reserved. Software written by Ian F. Darwin and others.
* $Id: BuzzInServlet.java,v 1.15 2004/03/26 03:30:22 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>");
}
}
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