[JAVA] Specify the encoding of static resources in Spring Boot

Spring Boot has the ability to host static resources (https://docs.spring.io/spring-boot/docs/current/reference/html/boot-features-developing-web-applications.html#boot- There is features-spring-mvc-static-content), but unlike the response from Controller, I was addicted to not giving charset to Content-Type in the response header of the static resource.

Expected response header

Content-Type: text/html;charset=UTF-8

Actual response header

Content-Type: text/html

Confirmation environment


You can specify the encoding for files with a specific extension by implementing WebServerFactoryCustomizer to customize the behavior of the built-in Tomcat container. However, only if the charset is uniquely determined for the extension.

import org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory;
import org.springframework.boot.web.server.MimeMappings;
import org.springframework.boot.web.server.WebServerFactoryCustomizer;
import org.springframework.stereotype.Component;

public class ServletCustomizer implements WebServerFactoryCustomizer<TomcatServletWebServerFactory> {

    public void customize(TomcatServletWebServerFactory factory) {
        MimeMappings mappings = new MimeMappings(MimeMappings.DEFAULT);
        mappings.add("html", "text/html;charset=UTF-8");

Bot plan

I will leave a few ideas I tried before I got here.

1. Customize CharacterEncodingFilter

By adjusting the setting of application.properties, the behavior of CharacterEncodingFilter can be changed. You can change it and force the charset to be output.


# Charset of HTTP requests and responses. 
# Whether to force the encoding to the configured charset on HTTP responses.

It works as expected for HTML files, but as the name suggests, it is forcibly added to image files, etc., which is a shame.

Content-Type: image/jpeg;charset=UTF-8

2. Extension of CharacterEncodingFilter

CharacterEncodingFilter outputs uniformly, so it seems good to derive this class and implement your own filter.

At first glance it seems to work, but this method is limited to cases where it can be uniquely determined from the request URL.

If you are doing something like returning index.html as a fallback page if the path cannot be resolved (as I did in my case), the request URL will not necessarily include the extension. Not always, so there is not enough information to make the decision.

public class WebMvcConfig extends WebMvcConfigurerAdapter {

    public void addResourceHandlers(ResourceHandlerRegistry registry) {
            .addResolver(new PathResourceResolver() {
                protected Resource getResource(String resourcePath, Resource location) throws IOException {
                    Resource requestedResource = location.createRelative(resourcePath);
                    return requestedResource.exists() && requestedResource.isReadable()
                        ? requestedResource : new ClassPathResource("/static/index.html");

Reference information

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