I am trying to learn a bit more on Object Oriented Programming.

In this exercise, I do not want to use any Container such as Spring or Glassfish. I am deploying my application to Tomcat. I only use JPA. What I want to achieve is to follow best practices and OOP Concepts correctly, and a good separation of concerns and layering.

Let me add my code here, I have a database table like this:

and here is my Entity:

This is my PersistenceUtil class:

and in my Web Application I have a ContextListener

#2 Is it ok that the DAO Layer requires an EntityManager and assumes that its transaction has already begun? Should it be the DAOs responsibility to obtain the EntityManager and/or begin/commit transaction?

#3 Again, I have the same questions on my mind. Is this class a mess like this? It does not have any dependencies, it obtains its EntityManager from the PersistenceUtil class in the Constructor. Is this ok? How about the entityManager field and starting / committing transactions which surrounds DAO calls?

#4 Is it ok that the Servlet initialises a Service Object for each call? Or should it have a private static Service object?(I think not, but I am not sure thus asking..)

Thank you very much for your time.

In this exercise, I do not want to use any container such as Spring or Glassfish. I am deploying my application to Tomcat. I only use JPA. What I want to achieve is to follow best practices and OOP concepts correctly, and a good separation of concerns and layering.

I have a database table like this:

and here is my Entity:

This is my PersistenceUtil class:

and in my web application I have a ContextListener:

#2 Is it ok that the DAO Layer requires an EntityManager and assumes that its transaction has already begun? Should it be the DAOs responsibility to obtain the EntityManager and/or begin/commit transaction?

#3 Again, I have the same questions on my mind. Is this class a mess like this? It does not have any dependencies, it obtains its EntityManager from the PersistenceUtil class in the Constructor. Is this ok? How about the entityManager field and starting / committing transactions which surrounds DAO calls?

#4 Is it ok that the Servlet initialises a Service object for each call? Or should it have a private static Service object?(I think not, but I am not sure thus asking..)