How do I use Spring Boot to serve static content located in Dropbox folder?

You can add your own static resource handler (it overwrites the default), e.g.

@Configuration
public class StaticResourceConfiguration extends WebMvcConfigurerAdapter {
    @Override
    public void addResourceHandlers(ResourceHandlerRegistry registry) {
        registry.addResourceHandler("/**").addResourceLocations("file:/path/to/my/dropbox/");
    }
}

There is some documentation about this in Spring Boot, but it’s really just a vanilla Spring MVC feature.

Also since spring boot 1.2 (I think) you can simply set spring.resources.staticLocations.