Jpa 的Persistence.xml配置讲解

<?xml version="1.0"?>  

<persistence xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd" version="1.0">  

<persistence-unit name="itcast" transaction-type="RESOURCE_LOCAL">  

   <properties>
    <property name="hibernate.dialect" value="org.hibernate.dialect.MySQL5Dialect" />
    <property name="hibernate.connection.driver_class" value="org.gjt.mm.mysqlDriver" />
    <property name="hibernate.connection.username" value="root" />
    <property name="hibernate.connection.password" value="root" />
    <property name="hibernate.connection.url" value="jdbc.mysql://localhost:3306/testdatabase?useUnicode=true&characterEncoding=UTF-8" />
    <property name="hibernate.max_fetch_depth" value="3" />
    <property name="hibernate.show_sql" value="true" />
    <property name="hibernate.hbm2ddl.auto" value="create-drop"/>
   </properties>  

</persistence-unit>

下面是从网上搜索回来的配置文件每行说明:

<?xml version="1.0" encoding="UTF-8"?>  

<persistence version="1.0"
xmlns:persistence="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence persistence_1_0.xsd ">  

<!--
     Name属性用于定义持久化单元的名字 (name必选,空值也合法);
     transaction-type 指定事务类型(可选)
-->
<persistence-unit name="unitName" transaction-type="JTA">  

   <!-- 描述信息.(可选) -->
   <description> </description>  

   <!-- javax.persistence.PersistenceProvider接口的一个实现类(可选) -->
   <provider>   </provider>  

   <!-- Jta-data-source和 non-jta-data-source用于分别指定持久化提供商使用的JTA和/或non-JTA数据源的全局JNDI名称(可选) -->
   <jta-data-source>java:/MySqlDS</jta-data-source>
   <non-jta-data-source> </non-jta-data-source>  

   <!-- 声明orm.xml所在位置.(可选) -->
   <mapping-file>product.xml</mapping-file>  

   <!-- 以包含persistence.xml的jar文件为基准的相对路径,添加额外的jar文件.(可选) -->
   <jar-file>../lib/model.jar</jar-file>  

   <!-- 显式列出实体类,在Java SE 环境中应该显式列出.(可选) -->
   <class>com.domain.User</class>
   <class>com.domain.Product</class>  

   <!-- 声明是否扫描jar文件中标注了@Enity类加入到上下文.若不扫描,则如下:(可选) -->
   <exclude-unlisted-classes/>  

   <!--   厂商专有属性(可选)   -->
   <properties>
    <!-- hibernate.hbm2ddl.auto= create-drop / create / update -->
    <property name="hibernate.hbm2ddl.auto" value="update" />
    <property name="hibernate.show_sql" value="true" />
   </properties>  

</persistence-unit>  

</persistence>