Tutorials : Server-Side Web Applications Using Servlets and JSP :
: Handling Cookies

Contents
Overview of Cookies
The Servlet Cookie API
Some Minor Cookie Utilities
Example: A Customized Search Engine Interface

4. Example: A Customized Search Engine Interface

Here's a variation of the SearchEngines example shown in the section on the HTTP status line. In this version, the front end is dynamically generated instead of coming from a static HTML file. Then, the servlet that reads the parameters and forwards them to the appropriate search engine also returns cookies to the client that list these values. Next time the client visits the front end, the cookie values are used to preload the form fields with the most recently used entries.

4.1 SearchEnginesFrontEnd.java

This servlet builds the form-based front end to the search engine servlet. At first blush, the output looks just like the page given by the static HTML page presented in the section on HTTP status codes. Here, however, selected values are remembered in cookies (set by the CustomizedSearchEngines servlet that this page sends data to), so if the user comes back to the same page at a later time (even after quitting the browser and restarting), the page is initialized with the values from the previous search.

You can also download the source. Note that code uses ServletUtilities.java, for the getCookieValue method (shown above) and for headWithTitle for generating part of the HTML. It also uses the LongLivedCookie class, shown above, for creating a Cookie that automatically has a long-term expiration date. 

package hall;

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.net.*;

public class SearchEnginesFrontEnd extends HttpServlet {
  public void doGet(HttpServletRequest request,
                    HttpServletResponse response)
      throws ServletException, IOException {
    Cookie[] cookies = request.getCookies();
    String searchString =
      ServletUtilities.getCookieValue(cookies,
                                      "searchString",
                                      "Java Programming");
    String numResults =
      ServletUtilities.getCookieValue(cookies,
                                      "numResults",
                                      "10");
    String searchEngine =
      ServletUtilities.getCookieValue(cookies,
                                      "searchEngine",
                                      "google");
    response.setContentType("text/html");
    PrintWriter out = response.getWriter();
    String title = "Searching the Web";
    out.println(ServletUtilities.headWithTitle(title) +
                "<BODY BGCOLOR=\"#FDF5E6\">\n" +
                "<H1 ALIGN=\"CENTER\">Searching the Web</H1>\n" +
                "\n" +
                "<FORM ACTION=\"/servlet/hall.CustomizedSearchEngines\">\n" +
                "<CENTER>\n" +
                "Search String:\n" +
                "<INPUT TYPE=\"TEXT\" NAME=\"searchString\"\n" +
                "       VALUE=\"" + searchString + "\"><BR>\n" +
                "Results to Show Per Page:\n" +
                "<INPUT TYPE=\"TEXT\" NAME=\"numResults\"\n" +
                "       VALUE=" + numResults + " SIZE=3><BR>\n" +
                "<INPUT TYPE=\"RADIO\" NAME=\"searchEngine\"\n" +
                "       VALUE=\"google\"" +
                checked("google", searchEngine) + ">\n" +
                "Google |\n" +
                "<INPUT TYPE=\"RADIO\" NAME=\"searchEngine\"\n" +
                "       VALUE=\"infoseek\"" +
                checked("infoseek", searchEngine) + ">\n" +
                "Infoseek |\n" +
                "<INPUT TYPE=\"RADIO\" NAME=\"searchEngine\"\n" +
                "       VALUE=\"lycos\"" +
                checked("lycos", searchEngine) + ">\n" +
                "Lycos |\n" +
                "<INPUT TYPE=\"RADIO\" NAME=\"searchEngine\"\n" +
                "       VALUE=\"hotbot\"" +
                checked("hotbot", searchEngine) + ">\n" +
                "HotBot\n" +
                "<BR>\n" +
                "<INPUT TYPE=\"SUBMIT\" VALUE=\"Search\">\n" +
                "</CENTER>\n" +
                "</FORM>\n" +
                "\n" +
                "</BODY>\n" +
                "</HTML>\n");
  }

  private String checked(String name1, String name2) {
    if (name1.equals(name2))
      return(" CHECKED");
    else
      return("");
  }
}

NEXT

This tutorial is now available as a book: Core Servlets and JavaServer Pages by Marty Hall, published by Sun Microsystems Press. Read all about it at CoreServlets.com
Server-Side Web Applications using Java Servlets versions 2.1/2.2 and JavaServer Pages (JSP) version 1.0: A Tutorial
© 1999-2000 Marty Hall.
All source code freely available for unrestricted use.
Created for work in the Research and Technology Development Center of the Johns Hopkins University Applied Physics Lab, for courses in the Johns Hopkins Part-Time MS Program in Computer Science, and for various industry seminars and on-site Java short courses.
Please note that this is a first draft of the tutorial, so please send corrections, comments, and suggestions to me at hall@apl.jhu.edu.
Reprinted with permission from the author. Click here to visit the original version

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