体系结构概述

Hibernate, as an ORM solution, effectively "sits between" the Java application data access layer and the Relational Database, as can be seen in the diagram above. Hibernate作为一个ORM解决方案，有效地连接Java应用程序数据访问层和关系数据库，如上图所示。 The Java application makes use of the Hibernate APIs to load, store, query, etc its domain data. Java应用程序利用Hibernate API来加载，存储，查询等其域数据。 Here we will introduce the essential Hibernate APIs. 这里我们将介绍基本的Hibernate API。 This will be a brief introduction; we will discuss these contracts in detail later. 这将是一个简单的介绍; 我们将在后面详细讨论这些内容。

As a JPA provider, Hibernate implements the Java Persistence API specifications and the association between JPA interfaces and Hibernate specific implementations can be visualized in the following diagram: 作为JPA提供者，Hibernate实现了Java Persistence API规范，JPA接口和Hibernate特定实现之间的关联可以在下图中查看：

SessionFactory (org.hibernate.SessionFactory)

A thread-safe (and immutable) representation of the mapping of the application domain model to a database.Acts as a factory for org.hibernate.Session instances. The EntityManagerFactory is the JPA equivalent of a SessionFactory and basically those two converge into the same SessionFactory implementation.A SessionFactory is very expensive to create, so, for any given database, the application should have only one associated SessionFactory.

SessionFactory作为org.hibernate.Session实例的工厂，是应用程序域模型到数据库的映射的线程安全（和不可变）表示。JPA内的EntityManagerFactory对象等价于一个SessionFactory对象，基本上这两个对象是放到同一个SessionFactory实现中。 创建一个SessionFactory是非常耗费资源的，所以，对于任何给定的数据库，应用程序应该只有一个相关联的SessionFactory。

The SessionFactory maintains services that Hibernate uses across all Session(s) such as second level caches, connection pools, transaction system integrations, etc.

SessionFactory保持Hibernate在所有“会话”中使用的服务，例如第二级缓存，连接池，事务系统集成等。

Session (org.hibernate.Session) A single-threaded, short-lived object conceptually modeling a "Unit of Work". Session表示应用程序与持久储存层之间交互操作的一个单线程对象，此对象生存期很短。

In JPA nomenclature, the Session is represented by an EntityManager. 在JPA命名法中，Session由EntityManager表示。

Behind the scenes, the Hibernate Session wraps a JDBC java.sql.Connection and acts as a factory for org.hibernate.Transaction instances.It maintains a generally "repeatable read" persistence context (first level cache) of the application domain model. 在幕后，HibernateSession封装一个JDBCjava.sql.Connection对象，并作为org.hibernate.Transaction实例的工厂。它维护应用程序域模型的一般“可重复读”持久性上下文（第一级缓存）。

Transaction (org.hibernate.Transaction) A single-threaded, short-lived object used by the application to demarcate individual physical transaction boundaries. 应用程序用来指定原子操作单元范围的对象，它是单线程的，生命周期很短。

EntityTransaction is the JPA equivalent and both act as an abstraction API to isolate the application from the underlying transaction system in use (JDBC or JTA). Transaction与JPA中的EntityTransaction是等价的，并且都充当抽象API，以将应用程序与正在使用的底层事务系统（JDBC或JTA）隔离。