public AbstractJettyServiceBuilder handler(Handler handler) {
        this.handler = requireNonNull(handler, "handler");
        return this;
    }
Sets the {@link Handler} of the Jetty {@link Server}.

@see Server#setHandler(Handler)
jetty/jetty11/src/main/java/com/linecorp/armeria/server/jetty/AbstractJettyServiceBuilder.java