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
.