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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