Mark Dixon 1 03 – Passing Data between pages: Forms, Sessions, & Query Strings

Mark Dixon 2 Session Aims & Objectives Aims –To introduce the fundamental ideas involved in passing data between pages Objectives, by end of this week’s sessions, you should be able to: –pass data between pages, using: Self Posting Query Strings Session Variables Cookies

Mark Dixon 3 Example: Logon v2 (design) Restrict access to home page

Mark Dixon 4 Example: Logon v2 (code) <% String un; String pw; String msg = ""; if (request.getParameter("btnLogon") != null){ un = request.getParameter("txtUserName"); pw = request.getParameter("txtPassWord"); if (un.equals("mark") && pw.equals("soft234")){ response.sendRedirect(“Home.html"); }else{ msg = "Login details incorrect."; } %> Please logon: Logon.jsp My Home page Welcome to my home page. Home.html

Mark Dixon 5 Example: Logon (Fixed Problem) View Source – shows client-side script: No server-side code

Mark Dixon 6 Example: Logon (Problem 2) User can type home page url (address) directly (bypassing logon page)

Mark Dixon 7 Solution Need way for: –password page to tell home page –that user logged in OK

Mark Dixon 8 Technique: Dead-Drop Variables 2 Spies wish to pass message between each other without actually meeting Arrange a dead-drop location –one spy leaves message at location –other spy visits location later to pick up message Variables used as dead-drop containers

Mark Dixon 9 <% Boolean LogonOK ; if ( LogonOK == false){ response.sendRedirect("Logon3.jsp"); } %> My Home page Welcome to my home page. Home3.jsp <% String un; String pw; String msg = ""; Boolean LogonOK; LogonOK = false; if (request.getParameter("btnLogon") != null){ un = request.getParameter("txtUserName"); pw = request.getParameter("txtPassWord"); if (un.equals("mark") && pw.equals("soft234")){ LogonOK = true; response.sendRedirect("Home3.jsp"); }else{ msg = "Login details incorrect."; } %> Please logon: Logon3.jsp Example: Logon v3 (code)  Does not work  Variables do not persist between pages LogonOK True

Mark Dixon 10 Example: Logon v3 (Error) Variables – don't persist between pages

Mark Dixon 11 Passing Data (temporary) Session object –used to pass information between pages: –exists for current session –persist between pages –clears if user closes browser –clears after 20 mins of inactivity –no need for declaration session.setAttribute("Thing", 91); Put 91 into Thing

Mark Dixon 12 Maintaining State: Session Object <% if (request.getParameter("btnSend") != null){ session.setAttribute("MSG", "Meet in BGB202"); }else if (request.getParameter("btnClear") != null){ session.invalidate(); } %> JSP Page Display Send.jsp Session variable –all objects –no declaration invalidate method –deletes all session variables

Mark Dixon 13 Maintaining State: Session Object <% String s = ""; if (session.getAttribute("MSG") != null){ s = session.getAttribute("MSG").toString(); } %> JSP Page Message: Display.jsp read session variable, and display

Mark Dixon 14 Example: Message Using Session variable: <% if (request.getParameter("btnSend") != null){ session.setAttribute("MSG", "Meet in BGB202"); }else if (request.getParameter("btnClear") != null){ session.invalidate(); } %> JSP Page Display Send.jsp <% String s = ""; if (session.getAttribute("MSG") != null){ s = session.getAttribute("MSG").toString(); } %> JSP Page Message: Display.jsp MSG Meet in BGB202

Mark Dixon 15 Questions: Session Variables Write a line of code to put the number 74 into a session variable called id. Write code that puts 'Hello' a variable called msg if the session variable called id is equal to 74 session.setAttribute("id", 74); if (session.getAttribute("id") == 74){ msg = "Hello"; }

Mark Dixon 16 Passing Data (temporary) Query Strings –Useful for passing information between pages via links

Mark Dixon 17 Maintaining State: Query Strings Data added to end of URL (address): page.jsp?Surname=Bob JSP code can use this data: –request.getParameter("Surname") would return the value "Bob" Form method=get –data automatically added to query string Query String

Mark Dixon 18 Example: Date-Time What background colour do you want for you date information? Yellow Light Blue Menu.jsp > The date is. DateTime.jsp

Mark Dixon 19 store small textual data on user's (client) computer –Actual location varies with platform (Windows, Linux, etc.) C:\Documents and Settings\UserName\Local Settings\Temporary Internet Files –e.g. (from session-id-time l amazon.co.uk/ Cookies: What

Mark Dixon 20 has 6 parts: –Name –Value –Domain –Path –Expiration –Security flag Name and Value are required –others have default values 20 Cookies: Parts

Mark Dixon 21 1.create cookie object 2.Constructor takes 2 parameters: –name and value (both Strings) 3.add cookie to response Cookies: Creating Cookie c; c = new Cookie("X", "23"); response.addCookie(c); Note: –any number of cookies can be created and added –cookies with same name are replaced

Mark Dixon 22 1.get cookies using request.getCookies –cookies are in an array 2.process the cookies: –use loop –getName returns name –getValue returns value Cookies: Reading Cookie[] cookies; cookies = request.getCookies(); for(int i=0; i<cookies.length; i++){ // cookies[i].getName() // cookies[i].getValue() }

Mark Dixon 23 browsers don’t always accept cookies –most modern browsers support cookies –still a few people using very old browsers often the user turns cookies off! –user concerned with what server is doing with information about them then probably turn cookies off can be used to transfer sensitive information in clear text NOT a serious security threat ( no viruses) Cookies: Disadvantages

Mark Dixon 24 Example: Message 2 (cookies) <% Cookie c; if (request.getParameter("btnSend") != null){ c = new Cookie("MSG", "Meet in SMB109"); c.setMaxAge(3600); // 1 hour (60 * 60) response.addCookie(c); }else if (request.getParameter("btnClear") != null){ c = new Cookie("MSG", null); c.setMaxAge(0); // delete cookie. response.addCookie(c); } %> JSP Page Display Send.jsp <% Cookie[] cookies; int i; String s = ""; cookies = request.getCookies(); if (cookies != null){ for(i=0; i<cookies.length; i++){ if (cookies[i].getName().equals("MSG")){ s += cookies[i].getValue() + " "; } %> JSP Page Message: Display.jsp MSG Meet in BGB202

Mark Dixon 25 Example: Message 2 (add cookies) <% Cookie c; if (request.getParameter("btnSend") != null){ c = new Cookie("MSG", "Meet in SMB109"); c.setMaxAge(3600); // 1 hour (60 * 60) response.addCookie(c); }else if (request.getParameter("btnClear") != null){ c = new Cookie("MSG", null); c.setMaxAge(0); // delete cookie. response.addCookie(c); } %> JSP Page Display Send.jsp Cookie c; if (request.getParameter("btnSend") != null){ c = new Cookie("MSG", "Meet in SMB109"); c.setMaxAge(3600); // 1 hour (60 * 60) response.addCookie(c); }else if (request.getParameter("btnClear") != null){ c = new Cookie("MSG", null); c.setMaxAge(0); // delete cookie. response.addCookie(c); }

Mark Dixon 26 Example: Message 2 (get cookies) <% Cookie[] cookies; int i; String s = ""; cookies = request.getCookies(); if (cookies != null){ for(i=0; i<cookies.length; i++){ if (cookies[i].getName().equals("MSG")){ s += cookies[i].getValue() + " "; } %> JSP Page Message: Display.jsp Cookie[] cookies; int i; String s = ""; cookies = request.getCookies(); if (cookies != null){ for(i=0; i<cookies.length; i++){ if (cookies[i].getName().equals("MSG")){ s += cookies[i].getValue() + " "; }

Mark Dixon 27 Reference: Server Object Model request object: calling web page –getParameter: used to get form and query-string data from page –getCookies: used to get cookie data from page response object: web page sent back –sendRedirect: used to navigate to other page session object: store data between pages –setAttribute: stores data –getAttribute: gets data –invalidate: clears session data

Mark Dixon 28 Passing Data (persistent) Cookies –stored on users’ (client) hard drive –persists between sessions –can be viewed by client –sent over http Database/file (covered in later lectures) –stored on server hard drive –persists between sessions –cannot be accessed directly by client

Mark Dixon 29 Tutorial Exercise: Message LEARNING OBJECTIVE: pass data between pages using session variables, and (form) self- posting Task 1: Get the message example working (from the lecture) Task 2: Change the send.jsp page so that when you click the buttons it gives some feedback as to what has happened.

Mark Dixon 30 Tutorial Exercise: Logon LEARNING OBJECTIVE: pass data between pages using session variables, and (form) self- posting Task 1: Type in the code for the Logon v3 example (from the lecture) NOTE: this will not work properly (variables do not persist between pages) Task 2: Modify this to use a session variable to 'remember' whether the logon was successful. Note: It should not be possible to view the source code Note: It should not be possible to bypass the logon

Mark Dixon 31 Tutorial Exercise: Date LEARNING OBJECTIVE: pass data between pages using query strings Task 1: Get the Date-Time example (from the lecture) working Task 2: Modify your page to provide another choice of background colour.

Mark Dixon 32 Tutorial Exercise: Message 2 LEARNING OBJECTIVE: pass data between pages using cookies Task 1: Get the message 2 example working (from the lecture) Task 2: Change the send.jsp page so that the user can change the text that is sent hint: add a text box