Control of the entire page cache and update dynamic pages as static pages

Static pages we all know, WEB server sends back the contents of the file comes with a Last-Modified header information, and static files last modification time stored inside, so that when the next time the browser requests the file will get Last -Modified header information exists with the If-Modified-Since sent to the server, telling the server's local cache last modification time, will first determine the end of the file when the server receives the time information of the If-Modified-Since request modify the time is later than this time, the late update, will retransmission of the contents of the file, along with the latest Last-Modified header information to the client, if the time is equal to or more than this time early, it shows no update cache fully synchronized, it will send back a 304 Not Modified status code, and to stop retransmission file content, and can save unnecessary data transmission.

Above is a static page cache and update the control mechanism, generally all this is by the WEB server directly arranged deal, all without user intervention. Dynamic pages are not so lucky, because of the dynamic page requests are forwarded by the WEB server to a specific page handler to complete their cache and update the strategic issues, and not arranged, so these controls must programmers to complete. Unfortunately, however, the dynamic page handler is unable to automatically handle cache is a whole page-level cache, we can cache a variable in the code so that at the next call, but still a lot of code to be executed, they can as static pages to the client a Last-Modified header information, determine the time and data updated when the next request, in order to decide whether to repeat the process and send data?

From the above analysis it is entirely feasible, but it needs to do special processing script, which is a logic to regulate this update detection, of course, this is not the focus on this. Because the the client to accept last modified time to completely rely on the Last-Modified header information, so dynamic scripting can be sent back to the content is also output a time as a basis to judge, then the next time the client requests the same page (accurately, should with a URL address), Last-Modified header information received will be appended to the If-Modified-Since request over. To a dynamic page here, we can get included with the request last modify time, then the first judgment point in time whether there is a new deal with the data, there is no new data, then, we are on the direct end of the current script, you can save server resources. Of course, before the end of the script, you need to play a 304 status code, because let clients sure to use the cache, must also be dependent on the status code, so just use dynamic script sends back a 304 Not Modified header information can not only saving server script execution resources, but also save the flow can be described as killing two birds with one stone, and the application form is more flexible and more controllable.