Java Q&A
by David Reilly
Example 1:
");
}
public void doPost(HttpServletRequest req,
HttpServletResponse res) throws IOException
{
ServletOutputStream out = res.getOutputStream();
res.setContentType ("text/html");
// Check to see if an email was submitted
String email = req.getParameter("email");
if (email != null)
{
// Store as a cookie
Cookie cookie = new Cookie("email", email);
res.addCookie(cookie);
}
// Check to see if an email was submitted
String name = req.getParameter("name");
if ( (name != null) && (!name.equals("")) )
{
// Store as a cookie
Cookie cookie = new Cookie("name", name);
res.addCookie(cookie);
}
out.println ("Thank you for registering");
out.println ("Click here to read cookie data");
}
}
Listing Two
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class ReadCookieServlet extends javax.servlet.http.HttpServlet
{
public void doGet(HttpServletRequest req,
HttpServletResponse res) throws IOException
{
String name = null;
String email = null;
ServletOutputStream out = res.getOutputStream();
res.setContentType ("text/html");
// Search for name & email address
Cookie list[] = req.getCookies();
for (int cookieIndex = 0;
cookieIndex < list.length; cookieIndex++)
{
String cookiename = list[cookieIndex].getName();
if ( cookiename.equals ("name") )
{
// Get cookie data value
name = list[cookieIndex].getValue() ;
}
else
if ( cookiename.equals("email") )
{
// Get cookie data value
email = list[cookieIndex].getValue() ;
}
}
if (name != null)
out.println ("Hello " + name + " ");
else
out.println ("Cookie 'name' not found ");
if (email != null)
out.println ("Your email is " + email + " ");
else
out.println ("Cookie 'email' not found ");
}
}
Listing Three
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class SessionCounterServlet extends javax.servlet.http.HttpServlet
{
public void doGet(HttpServletRequest req,
HttpServletResponse res) throws IOException
{
ServletOutputStream out = res.getOutputStream();
res.setContentType ("text/html");
// Get user session
HttpSession userSession = req.getSession(true);
// Check to see if there is a sessioncounter key
String sessionCounter =
(String) userSession.getValue("session_counter");
if (sessionCounter == null)
sessionCounter = "1";
else
{
// increment counter for each request
int count = Integer.parseInt(sessionCounter);
count++;
sessionCounter = String.valueOf(count);
}
// Place modified state data back in session
userSession.putValue("session_counter", sessionCounter);
out.println ("Number of times
visited this session : " + sessionCounter);
out.println (" Refresh this
page to see change in session count");
}
}
Listing Four
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class NoCookieSessionServlet extends javax.servlet.http.HttpServlet
{
// Context allows us to lookup sessions
private HttpSessionContext context;
public void doGet(HttpServletRequest req,
HttpServletResponse res) throws IOException
{
ServletOutputStream out = res.getOutputStream();
res.setContentType ("text/html");
try
{
// Get user session
// HttpSession userSession = req.getSession(true);
HttpSession userSession = getSession(req);
// Check to see if there is a sessioncounter key
String sessionCounter = (String) userSession.
getValue("no_cookie_session_counter");
if (sessionCounter == null)
sessionCounter = "1";
else
{
// increment counter for each request
int count = Integer.parseInt(sessionCounter);
count++;
sessionCounter = String.valueOf(count);
}
// Place modified state data back in session
userSession.putValue("no_cookie_session_counter",
sessionCounter);
out.println ("Number of times visited this session :
" + sessionCounter);
out.println (" Click here to reload this page");
// Output a dummy form, to test session-tracking
out.println ("");
}
catch(IllegalStateException ise)
{
out.println ("Invalid session");
}
}
public void doPost(HttpServletRequest req,
HttpServletResponse res) throws IOException
{
doGet(req,res);
}
private HttpSession getSession(HttpServletRequest req)
{
// Create a local variable to hold session
HttpSession session = null;
// Check to see if a session ID was specified as CGI paramater
String sessionID = req.getParameter ( "sessionid" );
// Check to see if this is the first invocation of the servlet
if ( (context == null) || ( sessionID == null) )
{
// Yes, so create brand new sessions.
session = req.getSession(true);
// If session context not stored, get for later
if (context == null)
context = session.getSessionContext();
}
else
{
// No, so we can attempt to look up the session
session = context.getSession (sessionID);
// Check to see session is really valid
if (session == null)
{
// No, so create a new one
session = req.getSession(true);
}
}
return session;
}
private String encodeUrl (String url, HttpSession session)
{
String sessionId = session.getId();
return ( url + "?sessionid=" + sessionId );
}
private String encodeForm (HttpSession session)
{
String sessionId = session.getId();
return ("");
}
}
5