If you remove Spring from the equation you need to build the servlets yourself (according to the Sevlet API). You probably package the servlets in a war-file (with some configuration files), the war-file can then be deployed in a servlet server (ie Tomcat,). The sevlet servser usually handles the thread pool and other resources (ie database connection pools) for you, so you "only" have to provide a servlet that... - Source: Reddit / 2 months ago
Do you know an article comparing Apache JMeter to other products?
Suggest a link to a post with product alternatives.