Thanks for your response.

I'm aware of different kind of implementation techniques, e.g. in DI (compile and runtime). This is also an important point in GraalVM and also in GWT, therefore you cannot use Spring in GWT for DI, but Dagger2 or compile time Gin (based on Guice), because GWT / J2CL transpiler just like GraalVM (not sure today) does not support reflections and co. Everything needs to be in the compile time.

But maybe because I'm working in different domains than you, I never see app performance with Spring runtime characteristic as a problem. Most of problems I see are application development problems (huge monolith apps, circular deps, bad encapsulation, ...). Also, data access performance with JPA Hibernate, SQL, but never because of Spring runtime capabilities.

I also never see Vert.x app in production so far but a lot of J2EE apps... So I cannot talk about Vert.x app.

In what domains would you see a performance problem with Spring runtime character?

Java as a client side webapp: I've seen a lot of mixed webapps (server-side JSP + jQuery for AJAX) and IMHO those webapps are really hard to manage and to extend. If you take a look at Angular webapps, they use the same structure as GWT webapps - only with different programming language. If you see Android UI development you will easily adapt GWT webapps since they also use the same structure. So, in my opinion in this case Java / GWT based UI development has done a lot of points correctly and they are already there since 2007.

One good example: GWT Turducken: https://de.slideshare.net/RobertKeane1/turducken-divide-and-conquer-large-gwt-apps-with-multiple-teams already talked about Micro Frontends in 2013 (almost 8 years ago). Definitely a must read and came from Google team which has to handle huge GWT webapps. The idea could be transferred in today JS webapps.

If you see the "components" hype in Angular, React and Vue.js (https://medium.com/swlh/web-apps-ui-development-trend-in-2020-components-to-rule-them-all-a9e2cb32d27), you will see that Java / GWT has this concept since 2007. The point is actually: few JS developers will learn Java to use GWT but if you are already a Java developer, why get less if you can get more?

Here is a real world example UI with Java / GWT very productive: https://www.youtube.com/watch?v=m226YJ91wJU

Here is an example of a component "composite" in Java - very OO, which Vue.js and co just tried today with "Single File Component": https://www.tutorialspoint.com/gwt/gwt_composite_widget.htm

Thanks a lot for your input!