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Beginning Active Server Pages

By James Crowley, published on 08 Mar 2002
James Crowley James first started this website when learning Visual Basic back in 1999 whilst studying his GCSEs. The site grew steadily over the years while being run as a hobby - to a regular monthly audience ...
Page 14 of 16
  1. Introduction
  2. Before you start
  3. Outputting Data
  4. Outputting Data 2
  5. Forms
  6. Forms 2
  7. Using Databases
  8. Using Databases 2
  9. Getting DB Content
  10. Query Strings
  11. Debugging
  12. Error Handling
  13. Including Files
  14. Making Content Expire
  15. Cookies
  16. Conclusion

Making Content Expire

A common problem when creating ASP pages is that although the data usually comes 'live' from the database, the browser often caches that information. Although this can help to reduce the bandwidth usage for your site, it also means that if the user has loaded the page before, he/she could be viewing out of date or inaccurate information.

There are a number of ways around this. First, you can set

Response.Expires = -1

which means that the page will always expire, and the browser will load a new copy. Alternatively, you can set a date on which the page will expire:

Response.ExpiresAbsolute = "5 December 2001"

or, simply the number of seconds in the future:

Response.Expires = 1000 'expires after 1000 seconds

However, in situations such as a shopping cart, even this is not enough. You will find that if the user presses the back button on their browser, more often that not, it doesn't bother re-loading the page... which can cause problems if the user has just completed the order, and then goes back to a full shopping cart. To get around this, there is one last trick... add this code:

'date in the past...
Response.AddHeader "Expires", "Mon, 26 Jul 1997 05:00:00 GMT"
'always modified
Response.AddHeader "Last-Modified", Now & " GMT"
'HTTP/1.1
Response.AddHeader "Cache-Control", "no-cache, must-revalidate"
'HTTP/1.0
Response.AddHeader "Pragma", "no-cache"
'last ditch attempt!
Response.Expires = -1

This code adds a number of fields to the header information sent to the browser, and seems to be effective whatever the browser!

Related tags

asp, visual basic

Comments

  1. michael poxon
    16 Dec 2006 at 21:38

        Hi,
    When I say I'm an ASP beginner, I mean it! I've only written one trivial bit of code, and got a blank page. I see now that's described in the article snippet below. I did indeed go to the saved .asp page on my hard drive!
    So my questions:
    I have XP, so IIS is presumably installed. In the snippet below, are 'localhost' and c:\inetpub\wwwroot the actual strings to type in? For example, I currently don't have a folder called "inetpub". Do I have to create one? And where on my actual server (starman.co.uk) should I put any ASP pages?
    Alternatively, is there a good introductory book you can recommend?

    • When you create an ASP page, you cannot view it on your hard disk by going to C:MyWebmyasppage.asp. It won't work! That references a direct page on your hard disk, and the server doesn't get a chance to parse any of the ASP code.
    • If you have IIS installed, it means your PC is a server (even if your PC is the only one which can access it)! You can access the pages on the server at http://localhost/ or http://PCName/. The physical location of your web site is by default C:\inetpub\wwwroot. Save your ASP pages there, and view them in a browser by visiting the URLs above.





  2. writetoksk
    04 Oct 2006 at 06:26

    hi,

    its first i started ASP.I want to know how to save the files.whats the extensions...Where can i get the sample programs

  3. James Crowley
    28 Dec 2004 at 08:13

    Are you running IIS ? And are you viewing it in your browser via the correct URL? (ie something starting with http:// rather than file:// ) ?

  4. James Crowley
    28 Dec 2004 at 08:12

    It does - you just can't see it We've got an ISAPI filter that rewritse /show/1010/ to something like /show.aspx?id=1010

  5. Sonic D Hedgehog
    12 Dec 2004 at 17:52

    Is there something special I have to do besides saving it as a .asp file, or does it just not work on my server? It just spits out the code, even HTML, as plain text.


    Code:
    <html>
    Let's see if ASP works!<br>
    <%
    Response.Write "Yep!"
    %>
    </html>

  6. Sonic D Hedgehog
    12 Dec 2004 at 17:46

    "The VB code can act on information passed to the page, such as from an internet form or a querystring (this is data passed in the URL after the ? ... take a look at this pages URL!)"


    http://www.developerfusion.com/show/1010 doesn't have a question mark in it...

  7. butro com
    31 Mar 2004 at 19:34

    you can not include a file from a remote storage site other than the one your website is being hosted on , like writing <!--#include file = " www.someplace.com/somefile.inc " --> but by using asp tear codes you can if you have any support this features.

  8. zabawka
    04 Feb 2004 at 21:30

    What do I do if I need to include a file from a remote storage site other than the one my website is being hosted on. The following doesn't work anymore


    <!--#include file = " www.someplace.com/somefile.inc " -->


    or even less the " virtual " call which starts searching the virtual directory the website is stored on.


    What now?


    Do I need to write a routine to access the file remotely then spilling it onto the page using response.write???



  9. James Crowley
    03 Feb 2004 at 10:58

    The trick for this is to get .NET to generate a TLB library for your the .NET class. In Vs.NET, you can modify the current build profile and set the "Register for COM Interop" section to true. See http://www.c-sharpcorner.com/Code/2002/April/COMInteropP2AJ.asp for more information.

  10. mak
    03 Feb 2004 at 08:58

    hi all,


            I am very new to ASP technology.  
            I am in a need to use DLLs (written in C#) in ASP Pages.
            Could anyone suggest me how to proceed.


    Regards,
    MAK,

  11. ushaRamesh
    02 Feb 2004 at 00:25

     i'd used ActiveX treeview control in my page and created tree by using ASP codings. but the tree is shown as collapsed one on load. i'd tried "TreeView1.Nodes(count).EnsureVisible " which produces an error of "index out of bounds". anyone pls help me as early as possible as i 've to complete by today itself. Thanks

  12. Alex
    05 Jan 2004 at 04:49

    thanks, but it wasn't the sql. i did that. it's long since solved.

  13. Anuradha Vasudeva
    05 Jan 2004 at 01:49

    chk your SQL statement. Stop before execting cConn.Execute sSQL . Print sSQL and try executing the same in the backend. If it doesnt work then you need to change the SQL statement.

  14. Alex
    13 Nov 2003 at 15:43

    i solved the problem a while ago, but i forgot how.

  15. zoglchaim
    12 Nov 2003 at 18:18

    heppens to be that i have the same prolem.

  16. kyayhmon
    21 Oct 2003 at 00:51

    I'm beginner of ASP.I make my thesis with ASP.But I've got problem for building project in Visual InterDev.I'd already installed IIS5.It shows web server can't connect.How I do?If it's cause of IIS error,please explain me step by step.let me know solution during five days.please help me.

  17. Alex
    15 Jul 2003 at 09:07

    It doesn't work it all. I created the table using Access and set of the OBDC fine. What's wrong?

  18. Alex
    15 Jul 2003 at 06:27

    I get this error when I submit forminput.asp:


    Microsoft OLE DB Provider for ODBC Drivers error '80040e14'


    [Microsoft][ODBC Microsoft Access Driver] Unknown


    /forminput.asp, line 12


    What's wrong? I even copied the code over exactly.
    the error's with this line:
    cConn.Execute sSQL

  19. ankush_vachher
    23 Jun 2003 at 02:54

    Quote:
    [1]Posted by JadesNet on 22 May 2003 09:07 AM[/1]
     I tried this code out exactly, but I get an INSERT INTO syntax error.  I have also tried using the rs.AddNew to add to my database but I get a read-only error.  I have tried changing the lock type and cursor types around but I can't get anything to work.


    pls see t he comment

  20. ankush_vachher
    23 Jun 2003 at 02:53

    U Have to include a file name adovbs.inc file i yr asp page. thenu can use the addnew and update methods

  21. JadesNet
    22 May 2003 at 09:07

     I tried this code out exactly, but I get an INSERT INTO syntax error.  I have also tried using the rs.AddNew to add to my database but I get a read-only error.  I have tried changing the lock type and cursor types around but I can't get anything to work.

  22. mallyone
    03 Jun 2002 at 20:39

    One thing to note, this only works on pages which have been posted to

  23. Developer Fusion Bot
    01 Jan 1999 at 00:00

    This thread is for discussions of Beginning Active Server Pages.

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