<?xml version="1.0" encoding="UTF-8" ?>  <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          http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd" version="1.0">   <persistence-unit name="demo" transaction-type="RESOURCE_LOCAL"><provider>org.hibernate.ejb.HibernatePersistence</provider><class>com.ncs.entity.UserInfo</class><properties>  <property name="hibernate.hbm2ddl.auto" value="update"/>  <property name="hibernate.connection.driver_class" value="oracle.jdbc.driver.OracleDriver"/>  <property name="hibernate.connection.url" value="jdbc:oracle:thin:@127.0.0.1:1522:xe"/>  <property name="hibernate.connection.username" value="system"/>  <property name="hibernate.connection.password" value="151923"/>  <property name="hibernate.dialect" value="org.hibernate.dialect.MySQLDialect"/>  <property name="hibernate.show_sql" value="true"/>  <property name="hibernate.format_sql" value="true"/>  </properties> </persistence-unit></persistence>

validate  update  create  create-drop

这几个参数的作用主要用于：自动创建  更新  验证数据库表结构

如果不是此方面的需求取none

validate：加载hibernate时，验证创建数据库表结构

create：每次加载hibernate，重新创建数据库表结构，这就是导致数据库表结构丢失的原因

create-drop：加载hibernate时创建，退出是删除表结构

update：加载hibernate自动更新数据库结构

常见问题排错:

1.

Exception in thread "main" javax.persistence.PersistenceException: No Persistence provider for EntityManager named HelloTitan at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:56) at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:34) at Main.main(Main.java:10)

原因：没有Persistence provider

解决办法：错误提示很明显:No Persistence provider.

(1)检查lib:jar丢失,则将需要的lib添加到classpath中，Jboss使用的是hibernate实现，这些lib在下面的目录中能找到

jboss-X\common\lib\

Exception in thread "main" javax.persistence.PersistenceException: [PersistenceUnit: HelloTitan] Unable to build EntityManagerFactory       at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:677)       at org.hibernate.ejb.HibernatePersistence.createEntityManagerFactory(HibernatePersistence.java:126)       at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:52)       at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:34)       at Main.main(Main.java:10)   Caused by: org.hibernate.HibernateException: Could not find datasource       at org.hibernate.connection.DatasourceConnectionProvider.configure(DatasourceConnectionProvider.java:79)       at org.hibernate.connection.ConnectionProviderFactory.newConnectionProvider(ConnectionProviderFactory.java:137)       at org.hibernate.ejb.InjectionSettingsFactory.createConnectionProvider(InjectionSettingsFactory.java:29)       at org.hibernate.cfg.SettingsFactory.buildSettings(SettingsFactory.java:89)       at org.hibernate.cfg.Configuration.buildSettings(Configuration.java:2101)       at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1325)       at org.hibernate.cfg.AnnotationConfiguration.buildSessionFactory(AnnotationConfiguration.java:867)       at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:669)       ... 4 more   Caused by: javax.naming.NoInitialContextException: Need to specify class name in environment or system property, or as an applet parameter, or in an application resource file:  java.naming.factory.initial       at javax.naming.spi.NamingManager.getInitialContext(NamingManager.java:645)       at javax.naming.InitialContext.getDefaultInitCtx(InitialContext.java:288)       at javax.naming.InitialContext.getURLOrDefaultInitCtx(InitialContext.java:325)       at javax.naming.InitialContext.lookup(InitialContext.java:392)       at org.hibernate.connection.DatasourceConnectionProvider.configure(DatasourceConnectionProvider.java:75)       ... 11 more  

java.naming.factory.initial=org.jnp.interfaces.NamingContextFactoryjava.naming.factory.url.pkgs=org.jboss.naming:org.jnp.interfacesjava.naming.provider.url=127.0.0.1:1099