Response.CacheControl

Response.CacheControl

The CacheControl property enables you to set the HTTP/1.1 Cache Control header in Response.Syntax.

The values for CacheControl are strings, and must be enclosed in quotation marks (" "). You must set CacheControl before any response is sent to the client, unless response buffering is enabled.

Syntax

Response.CacheControl [=Cache Control Header]

Parameters

Cache Control Header

The following is a partial list of values supported by the HTTP/1.1 Protocol. For more complete descriptions, see the Hypertext Transfer Protocol, HTTP/1.1 specification of section 14.9 on the World Wide Web Consortium Web site.

Value	Description
Private	A cache mechanism may cache this page in a private cache and resend it only to a single client. This is the default value. Most proxy servers will not cache pages with this setting.
Public	Shared caches, such as proxy servers, will cache pages with this setting. The cached page can be sent to any user.
No-cache	Do not cache this page, even if for use by the same client.
No-store	The response and the request that created it must not be stored on any cache, whether shared or private. The storage inferred here is nonvolatile storage, such as tape backups. This is not an infallible security measure.

Note

Between your Web server and a user requesting your page, there may be proxy servers configured to cache Web pages for faster response times. Usually ASP pages are developed to be unique for each user or may contain secure information. For this reason, IIS sets this property to "Private" so that proxy servers or other cache mechanisms will not cache pages. You can override this default value, setting it to any value supported by the HTTP/1.1 protocol. For more information, see the Hypertext Transfer Protocol, HTTP/1.1 specification of section 14.9 on the World Wide Web Consortium Web site.

If there is no cache mechanism between your Web server and a client computer, or if a proxy server is running HTTP/1.0, CacheControl will be ignored.

Setting CacheControl to "Public" may seem to improve the performance of your .asp files, but it is discouraged if you generate custom HTML for every request, and a proxy server might interfere with the response.

Applies To

Response Object

Example Code

CacheControl comes before the <HTML> tag to ensure that it is set before content is sent to the client.

--- CacheControl_NoBuffer.asp ---

<% 
  Response.Buffer = False 
  Response.CacheControl = "private" 
%> 
<HTML><HEAD><TITLE>Response.CacheControl Example</TITLE></HEAD> 
<BODY> 
Output from this page is sent to the client as it is being processed.<BR> 
It will not be cached.<BR> 
Today is <%= Date %>, <%= Time %><BR> 
<b>DO NOT ENTER CREDIT CARD  
    INFORMATION UNLESS YOU SEE HTTPS:// IN THE ADDRESS BAR OF YOUR WEB BROWSER,  
    AS THIS INDICATES A SECURE SOCKETS LAYER (SSL) CONNECTION.</b> 
<H3>Please enter your credit card number:</H3> 
<FORM NAME="Order" METHOD="POST" ACTION="order.asp "> 
<INPUT TYPE="TEXT" NAME="CreditCard"> 
<INPUT TYPE="SUBMIT" VALUE="Submit" NAME="Submit"> 
</FORM> 
</BODY> 
</HTML>

--- CacheControl_Buffer.asp ---

<% Response.Buffer = True %> 
<HTML><HEAD><TITLE>Response.CacheControl Example</TITLE></HEAD> 
<BODY> 
Output from this page is sent to the client once it is completely processed by the server, so we can set CacheControl anytime.<BR> 
<% Response.CacheControl = "private" %> 
It will not be cached.<BR> 
Today is <%= Date %>, <%= Time %><BR> 
<b>DO NOT ENTER CREDIT CARD  
    INFORMATION UNLESS YOU SEE HTTPS:// IN THE ADDRESS BAR OF YOUR WEB BROWSER,  
    AS THIS INDICATES A SECURE SOCKETS LAYER (SSL) CONNECTION.</b> 
H3>Please enter your credit card number:</H3> 
<H3>Please enter your credit card number:</H3> 
<FORM NAME="Order" METHOD="POST" ACTION="order.asp "> 
<INPUT TYPE="TEXT" NAME="CreditCard"> 
<INPUT TYPE="SUBMIT" VALUE="Submit" NAME="Submit"> 
</FORM> 
</BODY> 
</HTML>

Requirements

Client: Requires Windows XP Professional, Windows 2000 Professional, or Windows NT Workstation 4.0.

Server: Requires Windows Server 2003, Windows 2000 Server, or Windows NT Server 4.0.

Product: IIS

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