How to use browser cache to improve the access speed of Java websites?

How to use browser cache to improve the access speed of Java website?

Abstract: Browser cache is one of the important means to improve website performance. This article will introduce in detail how to use browser caching to improve the access speed of Java websites, and attach corresponding code examples.

1. Introduction to browser cache

1.1 What is browser cache?
Browser caching means that when the browser accesses a web page, it will store some or all of the resources of the web page (such as page files, pictures, scripts, style sheets, etc.) in the local hard disk or memory for the next visit. These resources can be read directly, thereby speeding up web page loading and reducing server load.

1.2 Implementation Principle
The implementation principle of browser caching is based on the caching mechanism in the HTTP protocol. When the server returns a response, it tells the browser how to cache resources by setting the Cache-Control, Expires, Last-Modified, and Etag fields in the HTTP response header, and determines whether the cache has expired on the next request, thereby deciding whether to use the cache directly. resource.

2. Use browser cache to improve the access speed of Java websites

2.1 Set HTTP response header
In Java websites, we can set appropriate fields in the HTTP response header. Control browser cache. The following are some commonly used settings:

// Allow caching of the HTML file of the current page
response.setHeader("Cache-Control", "public");
response.setHeader("Expires" , new Date(System.currentTimeMillis() 86400000).toGMTString()); // Set the cache time to one day

// Allow caching of image files of the current page
response.setHeader("Cache-Control ", "public, max-age=604800"); // Set the cache time to one week

// Allow caching of scripts and style sheet files of the current page
response.setHeader("Cache-Control" , "public, max-age=3600"); // Set the cache time to one hour

// Disable caching of the content of the current page
response.setHeader("Cache-Control", "no- cache, no-store, must-revalidate");
response.setHeader("Expires", "0");
response.setHeader("Pragma", "no-cache");

2.2 Client cache judgment
In a Java website, you can judge whether the client cache has expired by judging the If-Modified-Since and If-None-Match fields in the client request header. If the client cache has not expired, a 304 Not Modified response can be returned directly to avoid repeated loading of resources.

// Get the value of If-Modified-Since and If-None-Match fields
long ifModifiedSince = request.getDateHeader("If-Modified-Since");
String ifNoneMatch = request. getHeader("If-None-Match");

// Determine whether the cache has expired
if (ifModifiedSince > 0 && ifNoneMatch != null) {

// 根据日期和ETag判断缓存是否过期
if (ifModifiedSince >= lastModified && ifNoneMatch.equals(etag)) {
    response.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
    return;
}

}

2.3 Dynamically generate static resource files
In Java websites, dynamically generated pages, pictures, scripts and other resources can be cached and static files generated, thereby avoiding dynamically generating resources for each request and improving access speed. .

// Determine whether the static resource file already exists
File staticFile = new File(getServletContext().getRealPath("/") "/static/index.html");
if (! staticFile.exists()) {

// 动态生成静态资源文件
generateStaticFile();

}

// Return static resource file
response.sendRedirect(request.getContextPath() "/static/index.html");

3. Summary
By properly setting HTTP response headers, combined with client cache judgment and dynamic generation of static resource files, we can effectively use browser cache to improve the access speed of Java websites. In actual development, appropriate caching strategies can be flexibly selected according to specific needs, and performance testing and optimization can be performed to achieve a better user experience.

Reference code example: https://github.com/example/java-cache-example

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