Given that it was only added in Java 18 and it is a simple static file server (no way to run custom code when serving a URL), I don't think it's in any way widely used at the moment.
Edit: or will ever be. It is definitely explicitly not an equivalent of go's net/http. Indeed, there is probably never going to be an equivalent of net/http in the Java stdlib (since they prefer to rely on the user choosing one of the existing server frameworks, such as Jetty).
Yes, per the JEP that was linked, it is only intended as a toy server for quick example code, essentially:
> Provide a command-line tool to start a minimal web server that serves static files only. No CGI or servlet-like functionality is available. This tool will be useful for prototyping, ad-hoc coding, and testing purposes, particularly in educational contexts.
> It is not a goal to provide a feature-rich or commercial-grade server. Far better alternatives exist in the form of server frameworks (e.g., Jetty, Netty, and Grizzly) and production servers (e.g., Apache Tomcat, Apache httpd, and NGINX).
Edit: or will ever be. It is definitely explicitly not an equivalent of go's net/http. Indeed, there is probably never going to be an equivalent of net/http in the Java stdlib (since they prefer to rely on the user choosing one of the existing server frameworks, such as Jetty).