public interface Spring4limits
If you absolutely need to use Java 16+, you can remove Spring from the Smart GWT server by removing all of the Spring JARs from your WEB-INF/lib server directory:
and then removing the Spring configuration from your WEB-INF/web.xml:
  <!-- standard spring configuration -->
  <context-param>
      <param-name>contextConfigLocation</param-name>
      <param-value>/WEB-INF/applicationContext.xml</param-value>
  </context-param>    
  <listener>
      <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
  </listener>
  Note that Spring 5, which is compatible with JDK 16+, can be used in your application.  You
 just can't use Smart GWT's built-in Spring
 support,
  such as the "spring:" DMI target.SpringIntegration