// Purpose. 3 ways to pass "state" information from 1 HTTP request to another // 1) URL parameters // 2) HTML tags // 3) HttpSession object package testservlet; import java.io.PrintWriter; import java.io.IOException; import javax.servlet.http.*; public class ServletStateDemo extends HttpServlet { public void doPost( HttpServletRequest req, HttpServletResponse resp ) throws javax.servlet.ServletException, IOException { PrintWriter pw = resp.getWriter(); String state = req.getParameter( "state" ); String choice = req.getParameter( "choice" ); HttpSession session = req.getSession(); if (session != null) { String str = (String) session.getAttribute( "state" ); if (str != null) state = str; } pw.println( "Servlet State Demo" ); // URL parameters if (state == null) { pw.println( "Select a link:"); // "hidden" HTML tag } else if (state.equals("link")) { pw.println( "
" ); pw.println( "" ); pw.println( "Previous URL parameter was --- " + choice ); pw.println( "

Enter a string for \"hidden\":" ); pw.println( "" ); pw.println( "

" ); pw.println( "

" ); // setAttribute() } else if (state.equals("hidden")) { session.setAttribute( "state", "session" ); pw.println( "Previous text with \"hidden\" HTML tag was --- " + choice ); pw.println( "

Next" ); // invalidate() } else if (state.equals("session")) { session.invalidate(); pw.println( "Here is state.equals(\"session\")" ); pw.println( "

Top" ); } pw.println( "" ); pw.close(); } public void doGet( HttpServletRequest req, HttpServletResponse resp ) throws javax.servlet.ServletException, IOException { doPost( req, resp ); } }