DomUI is a stateful framework. This is quite a big advantage when you are writing code because there is no nonsense like serialization nor a need to write a zillion web services to service your page. For more advantages see here.
But having state in the server requires work, because state needs to be managed properly to prevent out of memory errors and database connection problems. This article describes how DomUI state management works.
DomUI state management handles at the very least the following:
- Database connections
- Hibernate sessions or JPA EntityManagers (persistence layer sessions)
- Page state and page objects.
Let's start by discussing the needs of the database layers: connection management and the persistence layer, then we'll look how DomUI handles those needs.
The persistence layer interface inside DomUI
DomUI is designed to be used with either Hibernate Classic or Hibernate JPA. Other persistance frameworks can be used but they will need an implementation of the supporting code for DomUI - look into the module domui-hibutil for details.
Both Hibernate Classic and JPA use two concepts that are very central to the concept of a persistence framework in Java, but they use different names:
- A Hibernate Session or a JPA EntityManager. We will call this the Session from now on because most of the discussion applies to either. The Session represents a database connection: it wraps a database connection and contains a stateful Object cache of Java entity POJO's that have been read using that interface. A key element here is that the Session maintains object identity: if a given record from the database is read multiple times each read, no matter where it comes from, returns the single object that represents that row in the database. This is a key requirement for writing proper and reliable business logic because it is very important that