Architecture Hibernate Gavin King, Christian Bauer, Max Rydahl Andersen, Emmanuel Bernard, and Steve Ebersole and thanks to James Cobb (Graphic Design) and Cheyenne Weaver (Graphic Design)

Gavin King, Christian Bauer, Max Rydahl Andersen, Emmanuel Bernard, and Steve Ebersole and thanks to James Cobb (Graphic Design) and Cheyenne Weaver (Graphic Design)

Architecture Hibernate

Sourse: http://www.hibernate.org/docs.html

Architecture

2.1. Overview

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

We do not have the scope in this document to provide a more detailed view of all the runtime architectures available; Hibernate is flexible and supports several different approaches. We will, however, show the two extremes: "minimal" architecture and "comprehensive" architecture.

This next diagram illustrates how Hibernate utilizes database and configuration data to provide persistence services, and persistent objects, to the application.

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:

SessionFactory (org.hibernate.SessionFactory)

A threadsafe, immutable cache of compiled mappings for a single database. A factory for Session and a client of ConnectionProvider, SessionFactry can hold an optional (second-level) cache of data that is reusable between transactions at a process, or cluster, level.

Session (org.hibernate.Session)

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.

Persistent objects and collections

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).

Transient and detached objects and collections

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.

Transaction (org.hibernate.Transaction)

(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. A Session might span several Transactions in some cases. However, transaction demarcation, either using the underlying API or Transaction, is never optional.

ConnectionProvider (org.hibernate.connection.ConnectionProvider)

(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.

TransactionFactory (org.hibernate.TransactionFactory)

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

Extension Interfaces

Hibernate offers a range of optional extension interfaces you can implement to customize the behavior of your persistence layer. See the API documentation for details.

Given a "minimal" architecture, the application bypasses the Transaction/TransactionFactory and/or ConnectionProvider APIs to communicate with JTA or JDBC directly.

2.2. Instance states

An instance of a persistent class can be in one of three different states. These states are defined in relation to a persistence context. The Hibernate Session object is the persistence context. The three different states are as follows:

transient

The instance is not associated with any persistence context. It has no persistent identity or primary key value.

persistent

The instance is currently associated with a persistence context. It has a persistent identity (primary key value) and can have a corresponding row in the database. For a particular persistence context, Hibernate guarantees that persistent identity is equivalent to Java identity in relation to the in-memory location of the object.

detached

The instance was once associated with a persistence context, but that context was closed, or the instance was serialized to another process. It has a persistent identity and can have a corresponding row in the database. For detached instances, Hibernate does not guarantee the relationship between persistent identity and Java identity.

2.3. JMX Integration

JMX is the J2EE standard for the management of Java components. Hibernate can be managed via a JMX standard service. AN MBean implementation is provided in the distribution: org.hibernate.jmx.HibernateService.

For an example of how to deploy Hibernate as a JMX service on the JBoss Application Server, please see the JBoss User Guide. JBoss AS also provides these benefits if you deploy using JMX:

Session Management: the Hibernate Session's life cycle can be automatically bound to the scope of a JTA transaction. This means that you no longer have to manually open and close the Session; this becomes the job of a JBoss EJB interceptor. You also do not have to worry about transaction demarcation in your code (if you would like to write a portable persistence layer use the optional Hibernate Transaction API for this). You call the HibernateContext to access a Session.
HAR deployment: the Hibernate JMX service is deployed using a JBoss service deployment descriptor in an EAR and/or SAR file, as it supports all the usual configuration options of a Hibernate SessionFactory. However, you still need to name all your mapping files in the deployment descriptor. If you use the optional HAR deployment, JBoss will automatically detect all mapping files in your HAR file.

Consult the JBoss AS user guide for more information about these options.Consult the JBoss AS user guide for more information about these options.

Another feature available as a JMX service is runtime Hibernate statistics. See Section 3.4.6, “Hibernate statistics” for more information.

2.4. JCA Support

Hibernate can also be configured as a JCA connector. Please see the website for more information. Please note, however, that at this stage Hibernate JCA support is under development.