4. Hibernate Architecture ~ JavaTechTube

Hibernate Architecture

The diagram below provides a high-level view of the Hibernate architecture:

Hibernate is flexible and supports several different approaches. We will, however, show the two extremes:-

The "minimal" architecture has the application provide its own JDBC connections and manage its own transactions. This approach uses a minimal subset of Hibernate's APIs:

The "comprehensive" architecture abstracts the application away from the underlying JDBC/JTA APIs and allows Hibernate to manage the details.

Here are some definitions of the objects depicted in the diagrams:

Configuration object is used to create a SessionFactory object which in turn configures Hibernate for the application using the supplied configuration file and allows for a Session object to be instantiated. The SessionFactory is a thread safe object and used by all the threads of an application.
The SessionFactory is a heavyweight object; it is usually created during application start up and kept for later use. You would need one SessionFactory object per database using a separate configuration file. So, if you are using multiple databases, then you would have to create multiple SessionFactory objects.

A single-threaded, short-lived object representing a conversation between the application and the persistent store.
It wraps a JDBC connection and is a factory for Transaction.
Session holds a mandatory first-level cache of persistent objects that are used when navigating the object graph or looking up objects by identifier.

Short-lived, single threaded objects containing persistent state and business function.
These can be ordinary JavaBeans/POJOs.
They are associated with exactly one Session.
Once the Session is closed, they will be detached and free to use in any application layer (for example, directly as data transfer objects to and from presentation).

Instances of persistent classes that are not currently associated with a Session.
They may have been instantiated by the application and not yet persisted, or they may have been instantiated by a closed Session.

(Optional) A single-threaded, short-lived object used by the application to specify atomic units of work.
It abstracts the application from the underlying JDBC, JTA or CORBA transaction.
This is an optional object and Hibernate applications may choose not to use this interface, instead managing transactions in their own application code.

(Optional) A factory for, and pool of, JDBC connections.
It abstracts the application from underlying Datasource or DriverManager.
It is not exposed to application, but it can be extended and/or implemented by the developer.

(Optional) A factory for Transaction instances.
It is not exposed to the application, but it can be extended and/or implemented by the developer.

(Optional) A factory for Transaction instances.
It is not exposed to the application, but it can be extended and/or implemented by the developer.

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