// Import I/O & servlet packages
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class HttpSessionExample extends javax.servlet.http.HttpServlet
{
// Implementation of GET request
public void doGet (HttpServletRequest request, HttpServletResponse response) throws IOException
{
// Assign a content type
response.setContentType( "text/html" );
// Prevent caching of server-side responses
response.setHeader( "Cache-Control" , "no-cache" );
// Create a stream for writing HTML output
PrintStream pout = new PrintStream (response.getOutputStream());
// Get the user session, and create one if one doesn't already exist
HttpSession userSession = request.getSession(true);
// Check for presence of state data in userSession
String background = (String) userSession.getValue("background");
String foreground = (String) userSession.getValue("foreground");
if (background == null)
{
// No background stored - place default value in session
background = getDefaultBackground();
userSession.putValue("background", background);
}
if (foreground == null)
{
// No foreground stored - place default value in session
foreground = getDefaultForeground();
userSession.putValue("foreground", foreground);
}
// Next, check for a change in parameter from FORM
if ( request.getParameter("background") != null)
{
background = request.getParameter("background");
userSession.putValue ("background", background);
}
if ( request.getParameter("foreground") != null)
{
foreground = request.getParameter("foreground");
userSession.putValue ("foreground", foreground);
}
pout.println ("<HTML><HEAD><TITLE>HttpSessionExample</TITLE></HEAD>");
pout.println ("<BODY BGCOLOR='" + background + "' TEXT='" + foreground + "'>");
pout.println ("This is an example of a servlet that uses HttpSession to store state info <p>\n");
// Print form
pout.println ("<form action='" + response.encodeUrl(request.getRequestURI()) + "' method=get>\n");
pout.println ("Background : <input type=text name=background value='" + background + "'><br>\n");
pout.println ("Foreground : <input type=text name=foreground value='" + foreground + "'><br>\n");
pout.println ("<input type=submit>");
pout.println ("</form>");
pout.println ("<a href='" + response.encodeUrl ( request.getRequestURI() ) + "'>Hyperlink example of URL rewriting</a> - not supported by all servers");<!--Broken Link? -->
pout.flush();
}
// Implemention of POST request
public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException
{
// Pass to doGet
doGet(request,response);
}
public String getDefaultBackground() { return "white"; }
public String getDefaultForeground() { return "black"; }
}
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