oh, thank you very much.
i think i probably understand that we could compile a java code like that with activiti lib to .class file and then put it to ./WEB-INF/classes/org/activiti/explorer/conf.
in this way, java bean can be much stronger, but compiling may increase the complexity.
today the deployment is in production environment, so i think i will still use 5.16.3 and wait for the official documentation for 5.16.4.