I get an error on this application that keeps users on a BD via a button on the index.html page that calls the servlet by clicking on POST. I would greatly appreciate a solu
Your stack trace tells you're using Tomcat.
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
Tomcat is not an EJB container. It's a barebones JSP/Servlet container. Throwing in a bunch of JARs in webapp's /WEB-INF/lib
just in order to get code to compile doesn't magically turn Tomcat into a true Java EE container.
For EJB, you need a real Java EE container. Replace Tomcat by TomEE, WildFly or Payara. Those are real Java EE containers supporting EJB, JPA, JSF, JAX-RS and all other real stuff out the box.