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

4.2 CustomizedSearchEngines.java

The SearchEnginesFrontEnd servlet shown above sends its data to the CustomizedSearchEngines servlet. In many respects, it is just like the SearchEngines servlet shown in the section on HTTP status codes. However, in addition to constructing a URL for a search engine and sending a redirection response to the client, the servlet also sends cookies recording the user data. These cookies will, in turn, be used by the servlet building the front end to initialize the entries in the HTML forms. 
package hall;

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

/** A varition of the SearchEngine servlet that uses
 *  cookies to remember users choices. These values
 *  are then used by the SearchEngineFrontEnd servlet
 *  to create the form-based front end with these
 *  choices preset.
 *  

 *  Part of tutorial on servlets and JSP that appears at
 *  http://www.apl.jhu.edu/~hall/java/Servlet-Tutorial/
 *  1999 Marty Hall; may be freely used or adapted.
 */

public class CustomizedSearchEngines extends HttpServlet {
  public void doGet(HttpServletRequest request,
                    HttpServletResponse response)
      throws ServletException, IOException {

    String searchString = request.getParameter("searchString");
    Cookie searchStringCookie =
      new LongLivedCookie("searchString", searchString);
    response.addCookie(searchStringCookie);
    searchString = URLEncoder.encode(searchString);
    String numResults = request.getParameter("numResults");
    Cookie numResultsCookie =
      new LongLivedCookie("numResults", numResults);
    response.addCookie(numResultsCookie);
    String searchEngine = request.getParameter("searchEngine");
    Cookie searchEngineCookie =
      new LongLivedCookie("searchEngine", searchEngine);
    response.addCookie(searchEngineCookie);
    SearchSpec[] commonSpecs = SearchSpec.getCommonSpecs();
    for(int i=0; i<commonSpecs.length; i++) {
      SearchSpec searchSpec = commonSpecs[i];
      if (searchSpec.getName().equals(searchEngine)) {
        String url =
          searchSpec.makeURL(searchString, numResults);
        response.sendRedirect(url);
        return;
      }
    }
    response.sendError(response.SC_NOT_FOUND,
                       "No recognized search engine specified.");
  }

  public void doPost(HttpServletRequest request,
                     HttpServletResponse response)
      throws ServletException, IOException {
    doGet(request, response);
  }
}

4.3 SearchEnginesFrontEnd Output

Here's the front end as it looks after the user types in some values or if the user comes back to the page in the same or a later session, after having typed in the values in the previous visit.

SearchEngines FrontEnd

4.4 CustomizedSearchEngines Output

CustomizedSearchEngines

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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