package coreservlets; import java.io.*; import javax.servlet.*; import javax.servlet.http.*; /** Servlet that attempts to give each user a unique * user ID. However, because it fails to synchronize * access to the nextID field, it suffers from race * conditions: two users could get the same ID. *

* Taken from Core Servlets and JavaServer Pages 2nd Edition * from Prentice Hall and Sun Microsystems Press, * http://www.coreservlets.com/. * © 2003 Marty Hall; may be freely used or adapted. */ public class UserIDs extends HttpServlet { private int nextID = 0; public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html"); PrintWriter out = response.getWriter(); String title = "Your ID"; String docType = "\n"; out.println(docType + "\n" + "" + title + "\n" + "

\n" + "\n" + "

" + title + "

\n"); String id = "User-ID-" + nextID; out.println("

" + id + "

"); nextID = nextID + 1; out.println(""); } }