Page cache and non-cache settings

The HTTP header of HTML controls the cache information of the page in several places, including browser, intermediate Cache Server (such as squid), and Web server. This article discusses the caching of HTML pages with Cache Control Information in the header (HTML pages generated by JSP/Servlet) on the intermediate cache server.

The header keywords about Cache in HTTP include Cache-Control (HTTP1.1), Pragma (HTTP1.0), last-Modified, and Expires.

HTTP1.0 Control page cache, which can be set to Pragma or no-cache. There are a lot of articles on the Internet that show you how to control the cache page from browsers or intermediate cache servers. The value is usually set to no-cache, but this value is not so safe, usually add Expires to 0 to achieve the goal. However, if we deliberately need the browser or cache server to cache our page, we need to set this value to Pragma.

Enable HTTP1.1 To control the page cache or not. Here we will introduce several common parameters:

• No-cache, browser and cache server should not cache page information;
• Public, the browser and cache server can cache page information;
• No-store, request and response information should not be stored in the disk system of the other party;
• Must-revalidate: for each client request, the proxy server must want the server to verify whether the cache is out of date;

Last-Modified: only the Last generation time of the page, in GMT format;

Expires period limit, in GMT format, indicates that the browser or cache server must obtain new page information from the Real Server after this time point;

The above two values are in the GMT format of the simplified type in JSP, and cannot take effect. The long type is only valid;

 

The following is a test example:

ServletA response. setContentType ("text/html" java. util. date date = response. setDateHeader ("Last-Modified", date. getTime (); response. setDateHeader ("Expires", date. getTime () + 20000); response. setHeader ("Cache-Control", "public"); response. setHeader ("Pragma", "Pragma"); System. out. println ("Access servlet" response. getWriter (). write ("Welcome to my homepage "}

To disable caching on the html page, add the following statement to the

 

Appendix: Role of meta in html pages

Meta is used to simulate HTTP Response Header packets in HTML documents. Meta Tags are used in

　　Name attribute

1. <meta name = "Generator" contect = ""> describes generation tools (such as Microsoft FrontPage 4.0;

2. <meta name = "KEYWords" contect = ""> describe KEYWords Of Your webpage to search engines;

3. <meta name = "DEscription" contect = ""> tell the search engine the main content of your site;

4. <meta name = "Author" contect = "Your name"> tell the search engine the creator of your site;

5. <meta name = "Robots" contect = "all | none | index | noindex | follow | nofollow">

The attributes are described as follows:

Set to all: the file will be retrieved, and the link on the page can be queried;

Set to none: files will not be retrieved, and links on the page cannot be queried;

Set to index: the file will be retrieved;

Set to follow: links on the page can be queried;

Set to noindex: the file will not be retrieved, but the link on the page can be queried;

Set to nofollow: files will not be retrieved, and links on the page can be queried.

　　Http-equiv attributes

1. <meta http-equiv = "Content-Type" contect = "text/html"; charset = gb_2312-80 ">

And <meta http-equiv = "Content-Language" contect = "zh-CN"> to describe the text and Language used by the homepage;

Also such as English is the ISO-8859-1 character set, there are BIG5, UTF-8, shift-Jis, Euc, Koi8-2 and other character sets;

2. <meta http-equiv = "Refresh" contect = "n; url = http: // yourlink"> regularly redirect a webpage to the http: // yourlink;

3. <meta http-equiv = "Expires" contect = "Mon, 12 May 2001 00:20:00 GMT"> you can set the expiration time of a webpage, once it expires, it must be called again on the server. Note that the GMT time format must be used;

4. <meta http-equiv = "Pragma" contect = "no-cache"> is used to disable the browser from accessing the page content from the cache of the local machine, once the page is set, it cannot be called out from the Cache;

5. <meta http-equiv = "set-cookie" contect = "Mon, 12 May 2001 00:20:00 GMT"> cookie setting: If the webpage expires, the cookie on the disk will be deleted. Note that the GMT time format must be used;

6. <meta http-equiv = "Pics-label" contect = ""> webpage rating: There is a content setting in internet Options of IE, it can prevent browsing of some restricted websites, and the website's restricted level is set through the meta attribute;

7. <meta http-equiv = "windows-Target" contect = "_ top"> force the page to be displayed on an independent page in the current window, it can prevent your webpage from being called as a frame page by others;

8. <meta http-equiv = "Page-Enter" contect = "revealTrans (duration = 10, transtion = 50) "> and <meta http-equiv =" Page-Exit "contect =" revealTrans (duration = 20, transtion = 6) "> set the special effect when you enter and Exit the Page, this function is called "format/Webpage transition" in FrontPage, but the page to be added cannot be a frame page.