How to Fix the “No Static Resource” Error After Upgrading Spring Boot 2.x to 3.x

Background

Upgrading a Spring Boot project from version 2.x to 3.x introduces Jakarta EE, which changes package names from javax.* to jakarta.* and may alter static‑resource handling. These changes frequently cause the runtime error No static resource when the application cannot locate static files.

Key Differences to Check

Servlet API : replace imports of javax.servlet with jakarta.servlet.

Static resource path : the default locations ( classpath:/static/, classpath:/public/) stay the same, but the property name may need explicit configuration via spring.web.resources.static-locations.

CORS configuration : .addAllowedOrigin("*") is deprecated; use .addAllowedOriginPattern("*") instead.

Custom WebMvc configuration : when providing a WebMvcConfigurer, you must explicitly add resource handlers for static files and WebJars.

Step‑by‑step Troubleshooting

Update Servlet imports Search the whole codebase for javax.servlet and replace it with jakarta.servlet .

import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

Explicitly configure static‑resource locations Add the following to your configuration files (both application.properties and application.yml are shown):

# application.properties
spring.web.resources.static-locations=classpath:/static/
spring.mvc.static-path-pattern=/**

# application.yml
spring:
  web:
    resources:
      static-locations: classpath:/static/
  mvc:
    static-path-pattern: "/**"

You can list multiple locations, e.g., classpath:/static/,classpath:/public/ .

Check custom WebMvcConfigurer If you have a custom MVC config class, ensure it registers static resource handlers:

import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.ResourceHandlerRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

@Configuration
public class WebConfig implements WebMvcConfigurer {
    @Override
    public void addResourceHandlers(ResourceHandlerRegistry registry) {
        // static resources
        registry.addResourceHandler("/**")
                .addResourceLocations("classpath:/static/");
        // WebJars
        registry.addResourceHandler("/webjars/**")
                .addResourceLocations("classpath:/META-INF/resources/webjars/");
    }
}

Update CORS configuration Replace the deprecated method with the new pattern‑based one:

configuration.addAllowedOriginPattern("*"); // ✅ new syntax

Verify the main class annotation Make sure the entry point is annotated with @SpringBootApplication so that auto‑configuration for static resources is enabled.

@SpringBootApplication
public class YourApplication {
    public static void main(String[] args) {
        SpringApplication.run(YourApplication.class, args);
    }
}

Practical Debugging Tips

Confirm that static files are packaged: check target/classes/static/ (Maven) or build/resources/main/static/ (Gradle). Missing files indicate a packaging issue rather than a Spring config problem.

Enable debug logging for Spring’s web modules to see how resource mappings are resolved:

logging.level.org.springframework.web=DEBUG
logging.level.org.springframework.boot.autoconfigure.web=DEBUG

After restarting, the logs will list the resolved static‑resource paths.

Other Common Upgrade Issues

JDK version: Spring Boot 3.x requires JDK 17 or higher.

Package migration: e.g., javax.validation → jakarta.validation.

Swagger compatibility: Swagger 2 is no longer supported; migrate to SpringDoc OpenAPI.

Spring Security: WebSecurityConfigurerAdapter is deprecated; use a SecurityFilterChain bean.

Third‑party libraries: ensure MyBatis, Druid, Sentinel, etc., have versions compatible with Spring Boot 3.x.

Conclusion

The root cause of the “No static resource” error after a Spring Boot upgrade is the Jakarta EE package migration combined with changed static‑resource configuration. The quickest fixes are to replace javax.* imports with jakarta.*, explicitly set spring.web.resources.static-locations, and, if needed, add proper resource handlers in a custom WebMvcConfigurer. Verifying that resources are packaged and enabling debug logs further speeds up troubleshooting.