package stocks; import java.io.*; import javax.servlet.*; import javax.servlet.http.*; import sun.misc.BASE64Decoder; /** Servlet that gives very hot stock tips. So hot that * only authorized users (presumably ones who have paid * the steep financial advisory fee) can access the servlet. *

* Taken from More Servlets and JavaServer Pages * from Prentice Hall and Sun Microsystems Press, * http://www.moreservlets.com/. * © 2002 Marty Hall; may be freely used or adapted. */ public class StockTip extends HttpServlet { /** Denies access to all users except those who know * the secret username/password combination. */ public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String authorization = request.getHeader("Authorization"); if (authorization == null) { askForPassword(response); } else { // Authorization headers looks like "Basic blahblah", // where blahblah is the base64 encoded username and // password. We want the part after "Basic ". String userInfo = authorization.substring(6).trim(); BASE64Decoder decoder = new BASE64Decoder(); String nameAndPassword = new String(decoder.decodeBuffer(userInfo)); // Decoded part looks like "username:password". int index = nameAndPassword.indexOf(":"); String user = nameAndPassword.substring(0, index); String password = nameAndPassword.substring(index+1); // High security: username must be reverse of password. if (areEqualReversed(user, password)) { showStock(request, response); } else { askForPassword(response); } } } // Show a Web page giving the symbol of the next hot stock. private void showStock(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html"); PrintWriter out = response.getWriter(); String docType = "\n"; out.println(docType + "\n" + "Hot Stock Tip!\n" + "\n" + "

Today's Hot Stock:"); for(int i=0; i<3; i++) { out.print(randomLetter()); } out.println("

\n" + ""); } // If no Authorization header was supplied in the request. private void askForPassword(HttpServletResponse response) { response.setStatus(response.SC_UNAUTHORIZED); // I.e., 401 response.setHeader("WWW-Authenticate", "BASIC realm=\"Insider-Trading\""); } // Returns true if s1 is the reverse of s2. // Empty strings don't count. private boolean areEqualReversed(String s1, String s2) { s2 = (new StringBuffer(s2)).reverse().toString(); return((s1.length() > 0) && s1.equals(s2)); } private final String ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"; // Returns a random number from 0 to n-1 inclusive. private int randomInt(int n) { return((int)(Math.random() * n)); } // A random letter from the alphabet. private char randomLetter() { return(ALPHABET.charAt(randomInt(ALPHABET.length()))); } }