Introduction
This article is next in the series of articles
about Java Servlet Session management. In this article we will learn about maintaining the client state or session by using URL Rewriting in a Servlet.
A Web container can use several methods to associate a session with a user, all
of which involve ing an identifier between the client and server. The
identifier can be maintained on the client as a cookie or the Web component can
include the identifier in every URL that is returned to the client.
Session Management Using URL Rewriting
Instead of Cookies:
In some situations, a browser or wireless
device may not accept cookies, which makes session tracking with cookies
impossible. URL rewriting provides you with another session tracking
alternative. that can be substituted automatically when Server detects that the
browser does not accept cookies. URL rewriting involves encoding the session ID
into the hyper-links on the Web pages that your servlet sends back to the
browser. When the user subsequently clicks these links, Server extracts the ID
from the URL address and finds the appropriate HttpSession when your servlet
calls the getSession() method.
If your application makes use of session objects, you must ensure that session
tracking is enabled by having the application rewrite URLs whenever the client
turns off cookies. You do this by calling the response's encodeURL(URL) method
on all URLs returned by a servlet. This method includes the session ID in the
URL only if cookies are disabled; otherwise, it returns the URL unchanged.
Usually, this technique is used when information that is to be transferred is
not very critical because the URL can be intercepted easily during transfer.
Given below the example of URL rewriting :
UrlRewritingServ.JAVA
import
java.io.IOException;
import
java.io.PrintWriter;
import
java.util.Date;
import
javax.servlet.ServletException;
import
javax.servlet.http.HttpServlet;
import
javax.servlet.http.HttpServletRequest;
import
javax.servlet.http.HttpServletResponse;
import
javax.servlet.http.HttpSession;
public
class
UrlRewritingServ
extends
HttpServlet
{
static
final
String
COUNTER_KEY
= "Counter.count";
public
void
doGet(HttpServletRequest req, HttpServletResponse resp)
throws
ServletException,IOException
{
HttpSession session = req.getSession(true);
resp.setContentType("text/html");
PrintWriter out = resp.getWriter();
int
count = 1;
String str ="Url
rewriting";
Integer i = (Integer) session.getAttribute(COUNTER_KEY);
if
(i !=
null)
{
count = i.intValue() + 1;
}
session.setAttribute(COUNTER_KEY,
new
Integer(count));
out.println("<BODY
BGCOLOR=\"yellow\">\n"
+
"<H1
ALIGN=\"CENTER\">"
+ str +
"</H1>\n"
+
"<H2>Information about Your Session:</H2>\n"
+
"<TABLE
BORDER=1 ALIGN=CENTER>\n"
+
"<TR
BGCOLOR=\"yellow\">\n"
+
" <TH>Info
Type<TH>Value\n"
+
"<TR>\n"
+
"
<TD>Session ID\n"
+
" <TD>"
+ session.getId() +
"\n"
+
"<TR>\n"
+
"
<TD>Creation Time\n"
+
" <TD>"
+
new
Date(session.getCreationTime()) +
"\n"
+
"<TR>\n"
+
"
<TD>Time of Last Access\n"
+
" <TD>"
+
new
Date(session.getLastAccessedTime()) +
"\n"
+
"<TR>\n"
+
"
<TD>Time out\n"
+
" <TD>"
+
new
Date(session.getMaxInactiveInterval()) +
"\n"
+
"<TR>\n"
+
"</TABLE>\n"
+
"</BODY></HTML>");
out.println("</b>
Number of Previous Accesses of this page <b>"
+ count+
"</b>
time(s) during this browser session");
String url = req.getRequestURI();
out.println("<form
method=GET action=\""
+ resp.encodeURL(url) +
"\">");
out.println("<input
type=submit "
+
"value=\"Hit page again\">");
out.println("</form>");
out.flush();
}
public
void
doPost(HttpServletRequest req, HttpServletResponse resp)
throws
ServletException,IOException
{
doGet(req, resp);
}
}
web.xml
<?xml
version="1.0"
encoding="UTF-8"?>
<web-app
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
id="WebApp_ID"
version="2.5">
<servlet>
<servlet-name>UrlRewritingServ</servlet-name>
<servlet-class>UrlRewritingServ</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>UrlRewritingServ</servlet-name>
<url-pattern>/UrlRewritingServ</url-pattern>
</servlet-mapping>
</web-app>
when you run this servlet the output is as
follows:
URL rewritting Ist:
![urlRewriting1st.gif]()
URL rewritting 2nd:
![urlRewriting2nd.gif]()
I think this article will be helpful to learn about Session management by URL
Rewriting in JAVA.