How to use browser cache to reduce server load and improve the access speed of Java websites?

How to use browser cache to reduce server load and improve the access speed of Java websites?

Abstract:
With the development of the Internet, the access speed of the website has become the focus of users. In Java website development, through reasonable use of browser cache, the server load can be effectively reduced and the website access speed can be improved. This article will introduce how browser caching works, and use Java code examples to illustrate how to use browser caching to improve website performance.

1. How browser caching works
Browser caching means that the browser saves the resources that have been visited in the local cache. When the user accesses the resource again, it reads it directly from the cache. , without the need to initiate a request to the server, thus improving access speed. Browser caching is generally divided into two types: strong caching and negotiated caching.

1. Strong caching
   Strong caching means that the browser loads resources directly from the cache and no longer sends requests to the server. Setting Expires or Cache-Control in the response header can control the expiration time of strong cache. Expires is an absolute time, while Cache-Control is a relative time.

For example, in Java, you can set Expires by setting the header of HttpServletResponse:

response.setHeader("Expires", "Wed, 21 Oct 2020 07:28:00 GMT");

or by setting Cache-Control:

response.setHeader("Cache-Control", "max-age=3600");

In this way, the resource can be The expiration time is set to 1 hour.

2. Negotiation cache
   Negotiation cache means that the browser sends a request to the server and determines whether the resource has expired based on the response header returned by the server. If the resource has not expired, status code 304 is returned, and the browser loads the resource directly from the cache; if the resource has expired, the resource is downloaded from the server again.

Setting Last-Modified and Etag in the response header can control the negotiation cache. Last-Modified represents the last modification time of the resource, and Etag is a unique identifier used to identify the version of the resource.

For example, in Java, you can set Last-Modified and Etag by setting the header of HttpServletResponse:

response.setHeader("Last-Modified", "Wed, 21 Oct 2020 07:28:00 GMT");
response.setHeader("Etag", "123456789");

When the browser requests the resource again, If will be included in the request header -Modified-Since and If-None-Match, the server determines whether the resource has expired by comparing these two values ​​​​with the Last-Modified and Etag of the resource.

2. Methods of using browser cache to improve access speed
In the development of Java websites, you can use the browser cache to improve access speed through the following methods:

1. Set reasonable cache control
   Set reasonable Expires, Cache-Control, Last-Modified and Etag according to the characteristics and change frequency of the resource. For static resources, the cache time can be set longer; for dynamic resources, the cache can be controlled by dynamically generating Last-Modified and Etag.

For example, for static resources:

response.setHeader("Expires", "Wed, 21 Oct 2022 07:28:00 GMT");
response.setHeader("Cache-Control", "max-age=31536000");

For dynamic resources:

String lastModified = generateLastModified(resource);
String etag = generateEtag(resource);
response.setHeader("Last-Modified", lastModified);
response.setHeader("Etag", etag);

2. Use version number to control cache
   For frequently updated resources, Cache can be controlled by changing the URL of the resource or adding a version number to the URL after each modification.

For example, add the version number to the URL of the resource:

String version = getVersion();
String url = "/static/js/main.js?v=" + version;

Every time you update the resource, you only need to modify the version number.

3. Set an appropriate caching strategy
   Set an appropriate caching strategy based on the characteristics and importance of the resource. For static resources and frequently accessed resources, the cache time can be set longer; for dynamic resources and resources that need to be updated in real time, the cache time can be set shorter.

For example, for static resources:

response.setHeader("Expires", "Wed, 21 Oct 2022 07:28:00 GMT");
response.setHeader("Cache-Control", "max-age=31536000");

For dynamic resources:

response.setHeader("Expires", "0");
response.setHeader("Cache-Control", "no-store, must-revalidate");

4. Resource merging and compression
   Combine multiple CSS or JavaScript files Merge into one file and compress the file size to reduce the number of requests and further improve access speed.

For example, merge and compress multiple CSS files:

List<String> cssFiles = Arrays.asList("style1.css", "style2.css");
String mergedCss = mergeAndCompressResources(cssFiles);
response.getWriter().write(mergedCss);

Conclusion:
By rationally utilizing browser cache, you can effectively reduce server load and improve the access speed of Java websites. . By setting reasonable cache control, complex version numbers, appropriate caching strategies, and resource merging and compression, website performance can be further improved and provide a faster and better user experience.

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