hibernate.hbm2ddl.auto=update

hibernate.cfg.xml配置如下<hibernate-configuration>  <session-factory>    <property name="hibernate.connection.driver_class">oracle.jdbc.driver.OracleDriver</property>    <property name="hibernate.connection.url">jdbc:oracle:thin:@localhost:1521:zy</property>    <property name="hibernate.connection.username">tom</property>    <property name="hibernate.connection.password">aaaaaa</property>    <property name="hibernate.dialect">org.hibernate.dialect.Oracle9Dialect</property>    <property name="hibernate.show_sql">true</property>    <property name="hibernate.hbm2ddl.auto">update</property>    <mapping resource="net/huadong/exammis/pojo/Person.hbm.xml"/>  </session-factory>
</hibernate-configuration>
update只是更新表结构，但不能生成请仔细参考一下hibernate.hbm2ddl.auto的配置参数，有以下四种: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数据丢失的原因。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