java persistence.xml_JPA的persistence.xml的使用及常见问题

在J2SE项目中:

http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd”version=”1.0″>

org.hibernate.ejb.HibernatePersistence

com.ncs.entity.UserInfo

注意:配置参数hibernate.hbm2ddl.auto 各个取值的含义

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\

(2)可能provider不对.检查xml文件里面的provider

2.

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

原因：JNDI没有初始化成功

解决办法： 在classpath添加 jnid.properties 文件 (以JBoss为例，配置如下)

java.naming.factory.initial=org.jnp.interfaces.NamingContextFactory

java.naming.factory.url.pkgs=org.jboss.naming:org.jnp.interfaces

java.naming.provider.url=127.0.0.1:1099

3.

程序成功运行，但是数据没有写入数据库

原因：没有提交数据

解决办法：em.getTransaction().commit();

附录

Hibernate SQL方言 (hibernate.dialect)

RDBMS方言

DB2

org.hibernate.dialect.DB2Dialect

DB2 AS/400

org.hibernate.dialect.DB2400Dialect

DB2 OS390

org.hibernate.dialect.DB2390Dialect

PostgreSQL

org.hibernate.dialect.PostgreSQLDialect

MySQL

org.hibernate.dialect.MySQLDialect

MySQL with InnoDB

org.hibernate.dialect.MySQLInnoDBDialect

MySQL with MyISAM

org.hibernate.dialect.MySQLMyISAMDialect

Oracle (any version)

org.hibernate.dialect.OracleDialect

Oracle 9i/10g

org.hibernate.dialect.Oracle9Dialect

Sybase

org.hibernate.dialect.SybaseDialect

Sybase Anywhere

org.hibernate.dialect.SybaseAnywhereDialect

Microsoft SQL Server

org.hibernate.dialect.SQLServerDialect

SAP DB

org.hibernate.dialect.SAPDBDialect

Informix

org.hibernate.dialect.InformixDialect

HypersonicSQL

org.hibernate.dialect.HSQLDialect

Ingres

org.hibernate.dialect.IngresDialect

Progress

org.hibernate.dialect.ProgressDialect

Mckoi SQL

org.hibernate.dialect.MckoiDialect

Interbase

org.hibernate.dialect.InterbaseDialect

Pointbase

org.hibernate.dialect.PointbaseDialect

FrontBase

org.hibernate.dialect.FrontbaseDialect

Firebird

org.hibernate.dialect.FirebirdDialect