This involves 4 kinds of header types:
Last-modified (last modification time);
Expires (validity period);
Pragma (compiling instructions);
Cache-control (cache control);
The first three headers belong to the HTTP1.0 standard. The header last-modified uses the UTC datetime value. If the cache system discovers that the last-modified value is more connected than the page cache version
Near the current time, he knew that a new version from the server should be used.
Expires indicates when the cached version should expire (Greenwich Mean Time). Setting it to a previous time forces the page on the server to be used.
pragma life how the page data should be processed. You can avoid caching the page in this way:
Header ("Pragma:no-cache");
The Cache-co0ntrol header is added in the HTTP1.1 to allow finer control (and should continue to use the HTTP1.0 header). The Cache-control settings are
Many, such as the following table:
| Instructions |
Meaning |
| Public |
Can be cached in any place |
| Private |
Can only be cached by the browser |
| No-cache |
cannot be cached anywhere |
| Must-revalidate |
Cache must check for updated versions |
| Proxy-revalidate |
The proxy cache must check for newer versions |
| Max-age |
The period in which content can be cached, expressed in seconds |
| S-maxage |
Overwrite max-age settings for shared cache |
The following example sets the browser's cache using the header ():
Copy CodeThe code is as follows:
Connect to the database:
$DBC = @mysqli_connect (' localhost ', ' username ', ' password ', ' Test ') OR die ('
Could not connect to the database!
');
Get the latest dates as timestamps:
$q = ' SELECT unix_timestamp (max (date_added)), Unix_timestamp (Max (date_completed)) from tasks ';
$r = Mysqli_query ($dbc, $q);
List ($max _a, $max _c) = Mysqli_fetch_array ($r, mysqli_num);
Determine the greater timestamp:
$max = ($max _a > $max _c)? $max _a: $max _c;
Create a cache interval in seconds:
$interval = 60 * 60 * 6; 6 hours
Send the header:
Header ("last-modified:".) Gmdate (' R ', $max));
Header ("Expires:".) Gmdate ("R", ($max + $interval)));
Header ("cache-control:max-age= $interval");
?>
1. After connecting to the database, get the latest date value date_added,date_completed in the data table, convert the return value to an integer with the Unix_timestamp () function, and get the maximum value assigned to $max.
2. Define a reasonable cache time.
Copy CodeThe code is as follows:
$interval =60*60*6
The reasonable value of the page itself, the number of visitors and page update frequency, the above code is 6 hours.
3. Send last-modified headers.
Copy CodeThe code is as follows:
Header ("last-modified:". Gmdate ("R", ($max + $interval)));
When the Gmdate () function uses the parameter "R", the corresponding date format is returned according to the HTTP specification.
4. Set the Expires headers.
Copy CodeThe code is as follows:
Header ("Expires:".) Gmdate ("R", ($max + $interval)));
5. Set the Cache_control headers.
Copy CodeThe code is as follows:
Header ("cache-control:max-age= $interval");
http://www.bkjia.com/PHPjc/322444.html www.bkjia.com true http://www.bkjia.com/PHPjc/322444.html techarticle This involves 4 kinds of header types: last-modified (last modified time); Expires (validity period); Pragma (compile instructions); Cache-control (cache control); The first three headers belong to the HTTP1.0 standard. ...
