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CIS 451: Cookies

CIS 451: Cookies. Dr. Ralph D. Westfall February, 2009. Problem. server mostly tracks requests for files very efficient for high volume of users memory doesn't know who is asking for files even if from link on file in same web site to help server, could send identification

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CIS 451: Cookies

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  1. CIS 451: Cookies Dr. Ralph D. Westfall February, 2009

  2. Problem • server mostly tracks requests for files • very efficient for high volume of users • memory doesn't know who is asking for files • even if from link on file in same web site • to help server, could send identification • identification needs to associated with all files requested by same user of application • use HTML "hidden fields" in later pages? <INPUT TYPE="hidden" NAME="[ ]" VALUE="[ ]">

  3. Possible Solutions • password login (+ hidden fields) • advantage: highest security • disadvantage: extra work for customer • automated identification (+ hidden) • could generate a random # to ID customer • advantage: no extra work for customer • disadvantage: only good for one session • can' track repeat visits by same person

  4. Another Solution: Cookies • information stored in file on client computer • National Semiconductor cookies policy • advantages • user only needs to enter data one time • data "persists," so it is available in later sessions • disadvantages • some users won't allow cookies (very few?) • cookies can be removed from user's computer • expire, replaced by newer ones, or cleared by user

  5. Cookies • cookies have names • a cookie can have multiple values • cookie data accessed by the cookie's name (and by the keys if more than one value) • cookies are part of both the Request and Response ASP intrinsic objects • created by Response.Cookies methods • stored in Request.Cookies "collection"

  6. Working with Cookies • creating • Response.Cookies("cookie")("key") = "value" • 'substitute "literals" or string variables for • 'items within " " • 'note similarities to selection of multiple • 'items in a ListBox on HTML or .NET form • deleting • Response.Cache.SetExpires _ 'line continuation • (DateTime.Now.AddDays(-5))'positive or negative • 'negative value deletes on client • 'but session still has data

  7. Using QueryString in an aspx File • can create the same effect sending from an aspx file as from a html file Response.Redirect("rsp.aspx?Name=" & _ this.txtName.Text & "&LastName=" & _ this.txtLastName.Text) • values are URL encoded and visible in browser address of destination page • one way to migrate from html to aspx

  8. Working with Cookies - 2 • accessing • strValue = Request.Cookies("cookie")("key") • 'note that data is accessed from Request object • counting cookies • intCount = Request.Cookies.Count + 1 • '0 based: need to add 1 to get actual #

  9. Viewing Cookies • install Web Developer add-on for Firefox • Cookies>View Cookie Information

  10. Cookie Exercise • create a web project in VB.NET • add one TextBox and a Button to the Default.aspx form • add another form named CookieRead.aspx and add a Label to it

  11. Cookie Exercise - 2 • double-click on each form to create the aspx.vb code-behind files • or right-click on the file names in Solution Explorer>View Code • download cookiewrite.aspx and cookieread.aspx from Code Samples • use the code examples to get the two pages to run

  12. Cookie Exercise - 3 • make enhancements • add some more input fields to Default.aspx and modify CookieRead.aspx to output these new fields • add a Button to reset TextBoxes to blanks rather than reloading cookie values • add Button to 2nd page to delete cookie

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