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How Java ensures that JS is not cached

Popularity：87 ℃/2024-10-21 11:24:47

Hello, I'm V. Today we're going to talk about Java backends making sure that JavaScript is not cached. Today we're going to talk about Java backends making sure that JavaScript isn't cached. First, let's understand why we need to do this, which usually stems from the following scenarios or problems:

1. First, a few questions

1. Documentation updates do not take effect in a timely manner

Browser caching mechanisms are designed to speed up loading and reduce server stress, but they can sometimes cause problems. When a JavaScript file is updated, if the browser loads the old version from the cache, the user is unable to see the newest features or bug fixes. example: a developer releases a new version of the front-end code that fixes a critical issue, but the user's browser is still using the old code from the cache, causing the issue to persist. Users may think that the site is not fixed or that a new issue has appeared, thus affecting the user experience.

2. Front-end and back-end inconsistencies

In Java Web applications, JavaScript is often used to interact with back-end services. If the version of the JavaScript code does not match the back-end logic, this can lead to incompatibility issues. For example, if the request format of the back-end interface changes, but the browser still uses the old JavaScript code, the communication between the client and the server fails and an error is generated.

3. Impact Debugging and Development

In development and debugging environments, caching can result in code changes not being instantly visible, which is very inconvenient for the debugging process. A developer may find that the modified code is not applied during debugging, resulting in wasted time. For example, if a developer modifies a JavaScript file, but the browser continues to execute the old code due to caching, the developer is unable to verify that the new code is correct, and may even assume that there is a problem with the code itself.

4. security issue

Old caches may expose pre-existing vulnerabilities in the system. Even if the backend has been upgraded to fix the security vulnerability, the browser may still be vulnerable if it loads an old JavaScript file. For example, let's say there is an XSS vulnerability in a particular version of JavaScript. Although the new version has fixed the vulnerability, the old files cached by the browser are still exposed to the risk of attack.

Therefore, if the front-end page is not able to respond to updates in a timely manner (e.g., fixing bugs, optimizing features, etc.), the user experience may be negatively impacted. Especially when doing product version iterations, caching issues may make new features appear to be not live, affecting user experience and satisfaction.

2. And what is to be done about it?

In Java Web development, to ensure that JavaScript files (or any static resources) are not cached by the browser, there are several experiences that can be used:

1. Use of version numbers or timestamps

Add a version number or timestamp to the URL of a JavaScript file so that the URL is different each time the file is updated, so that the browser thinks it's a new resource and reloads it. For example:

<script src="?v=1.0.1"></script>

Or use a dynamic timestamp:

<script src="?t=<%= () %>"></script>

In this way, each time a different query parameter is generated, the browser considers it a new file and does not read it from the cache.

2. Setting the HTTP response header

On a Java backend, such as Spring Boot or Servlet, you can control caching by setting HTTP headers. Common HTTP headers include:

  • Cache-Control: Control cache behavior.
  • Pragma: Controls caching behavior (mainly for HTTP/1.0 compatibility).
  • Expires: Set the time at which the resource expires.

Sample code (Spring Boot filter):

import ;
import ;
import ;
import ;
import ;
import ;
import ;
import ;

public class NoCacheFilter implements Filter {
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) 
        throws IOException, ServletException {
        
        HttpServletResponse httpResponse = (HttpServletResponse) response;
        ("Cache-Control", "no-store, no-cache, must-revalidate, max-age=0");
        ("Pragma", "no-cache");
        ("Expires", "0");
        
        (request, response);
    }

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {}

    @Override
    public void destroy() {}
}

3. Configuring caching policies for static resources

In a Spring Boot project, you can define caching policies for static resources through configuration classes. For example:

import ;
import ;
import ;

@Configuration
public class WebConfig implements WebMvcConfigurer {

    @Override
    public void addResourceHandlers(ResourceHandlerRegistry registry) {
        ("/js/**")
                .addResourceLocations("classpath:/static/js/")
                .setCachePeriod(0); // 0 Indicates no caching
    }
}

pass (a bill or inspection etc)setCachePeriod(0) Setting the cache period to 0 forces the browser to fetch the latest JavaScript file from the server every time.

4. UtilizationETag maybeLast-Modified

Set in the HTTP responseETag maybeLast-Modified, so that the browser asks the server if the resource has been updated on each request. If it hasn't changed, the server returns a 304 status code, thus avoiding unnecessary reloads.

Example (Settings)Last-Modified）：

("Last-Modified", ());

The above methods ensure that the browser gets the latest version of the JavaScript file in a timely manner and does not use cached old versions.

Some reflections on

The question arises, so when can I use the cache?

While caching may cause these problems, it doesn't mean that caching is never good. In some scenarios, using browser caching can significantly improve performance:

  • When static resources (e.g., JavaScript, CSS files) are changed less often, caching can significantly reduce network requests and increase page load speed.
  • Ensuring that caching mechanisms are effectively controlled at update time (e.g., using a file's version number or hash as part of the filename) can avoid unnecessary re-downloads and overloads.

How do you balance it?

Usually, we don't disable caching altogether, but rather balance performance and update issues through version numbers, hashes, cache control headers, etc. This way, the browser can utilize the cache when it's not necessary and get the latest resources when it's needed.Follow Vigo love programming, the code code through the smooth not lose hair。

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