📄 userids.java
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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.
* <P>
* 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 =
"<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.0 " +
"Transitional//EN\">\n";
out.println(docType +
"<HTML>\n" +
"<HEAD><TITLE>" + title + "</TITLE></HEAD>\n" +
"<CENTER>\n" +
"<BODY BGCOLOR=\"#FDF5E6\">\n" +
"<H1>" + title + "</H1>\n");
String id = "User-ID-" + nextID;
out.println("<H2>" + id + "</H2>");
nextID = nextID + 1;
out.println("</BODY></HTML>");
}
}
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