Title: HTML file caching mechanism and code examples
Introduction: When writing web pages, we often encounter browser cache problems. This article will introduce the caching mechanism of HTML files in detail and provide some specific code examples to help readers better understand and apply this mechanism.
1. Browser caching principle
In the browser, whenever a web page is accessed, the browser will first check whether there is a copy of the web page in the cache. If there is, the web page content is obtained directly from the cache. This is the basic principle of browser caching. The advantage of the browser caching mechanism is that it can improve web page loading speed, reduce network requests, and save bandwidth.
2. HTML caching methods
The caching of HTML files can be controlled in the following two ways:
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Expires and Cache-Control
Through Adding the Expires and Cache-Control fields to the HTTP response header can control the time the browser caches files. The specific sample code is as follows:HTTP/1.1 200 OK Content-Type: text/html Cache-Control: max-age=3600 Expires: Wed, 04 Aug 2022 08:00:00 GMT <!DOCTYPE html> <html> <!-- HTML页面内容 --> </html>
In the above sample code, the Cache-Control field specifies the maximum cache time of 3600 seconds, which is one hour, and the Expires field specifies the cache expiration time as August 4, 2022. 8 o'clock.
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Last-Modified and If-Modified-Since
Indicate the last modification time of the file by adding the Last-Modified field in the HTTP response header. After the browser caches the file, it will add the If-Modified-Since field the next time it requests the file and send the last modification time of the last cached file to the server. The server will determine whether the file has been updated based on this time. If the file is not updated, a 304 Not Modified response is returned and the browser continues to use the cached file. The specific sample code is as follows:HTTP/1.1 200 OK Content-Type: text/html Last-Modified: Mon, 01 Aug 2022 12:00:00 GMT <!DOCTYPE html> <html> <!-- HTML页面内容 --> </html>
In the above sample code, the Last-Modified field specifies the last modification time of the file as 12:00 on August 1, 2022.
3. Cache control strategy
According to actual needs, we can formulate different caching strategies based on the content of the file or other conditions to better control the browser cache.
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Static file caching
For static files that do not change frequently, you can set a longer cache time so that the browser can cache the file persistently and reduce requests to the server. For example, for static files such as CSS, JavaScript, and images, you can set the cache time to one year. The sample code is as follows:HTTP/1.1 200 OK Content-Type: text/css Cache-Control: max-age=31536000 /* CSS文件内容 */
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Dynamic file caching
For dynamic files that change frequently, you can control the cache time to be shorter to ensure that the browser can obtain the latest files in a timely manner. content. For example, dynamically generated HTML files can not set any cache fields, allowing the browser to request the latest version every time. The sample code is as follows:HTTP/1.1 200 OK Content-Type: text/html Cache-Control: no-cache, no-store, must-revalidate Pragma: no-cache Expires: 0 <!DOCTYPE html> <html> <!-- HTML页面内容 --> </html>
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Version control cache
Keep the file name unchanged when the file is updated, by adding a version number or timestamp to the file name or URL. Make the browser think it is a new file and reload the file. The sample code is as follows:<link rel="stylesheet" href="/static/style.css?v=1.0"> <script src="/static/script.js?t=1627836018"></script>
4. Summary
The caching of HTML files is achieved by setting the corresponding fields in the HTTP response header. By properly controlling cache time and policies, web page loading speed and user experience can be improved. In actual development, appropriate caching methods and strategies are selected based on the content and characteristics of the file. We hope that the code examples provided in this article can help readers better understand and use the HTML caching mechanism.
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