关于Hibernate的一个错误 Identifier text cannot be null

1.hibernate配置如下 :

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

<!DOCTYPE hibernate-configuration PUBLIC

	"-//Hibernate/Hibernate Configuration DTD 3.0//EN"

	"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>

	<session-factory>

	

		<!-- 

		#hibernate.dialect org.hibernate.dialect.MySQLDialect

		#hibernate.dialect org.hibernate.dialect.MySQLInnoDBDialect

		#hibernate.dialect org.hibernate.dialect.MySQLMyISAMDialect

		#hibernate.connection.driver_class com.mysql.jdbc.Driver

		#hibernate.connection.url jdbc:mysql:///test

		#hibernate.connection.username gavin

		#hibernate.connection.password

		 -->

		 <!-- 数据库驱动 -->

		<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>

		 <!-- 数据库url -->

		<property name="hibernate.connection.url">jdbc:mysql:///projectone</property>

		 <!-- 数据库连接用户名 -->

		<property name="hibernate.connection.username">root</property>

		 <!-- 数据库连接密码 -->

		<property name="hibernate.connection.password">root</property>

		<!-- 数据库方言

			不同的数据库中,sql语法略有区别. 指定方言可以让hibernate框架在生成sql语句时.针对数据库的方言生成.

			sql99标准: DDL 定义语言  库表的增删改查

					  DCL 控制语言  事务 权限

					  DML 操纵语言  增删改查

			注意: MYSQL在选择方言时,请选择最短的方言.

		 -->

		<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>

		

		

		<!-- #hibernate.show_sql true 

			 #hibernate.format_sql true

		-->

		<!-- 将hibernate生成的sql语句打印到控制台 -->

		<property name="hibernate.show_sql">true</property>

		<!-- 将hibernate生成的sql语句格式化(语法缩进) -->

		<property name="hibernate.format_sql">true</property>

		<!-- 

		## auto schema export  自动导出表结构. 自动建表

		#hibernate.hbm2ddl.auto create		自动建表.每次框架运行都会创建新的表.以前表将会被覆盖,表数据会丢失.(开发环境中测试使用)

		#hibernate.hbm2ddl.auto create-drop 自动建表.每次框架运行结束都会将所有表删除.(开发环境中测试使用)

		#hibernate.hbm2ddl.auto update(推荐使用) 自动生成表.如果已经存在不会再生成.如果表有变动.自动更新表(不会删除任何数据).

		#hibernate.hbm2ddl.auto validate	校验.不自动生成表.每次启动会校验数据库中表是否正确.校验失败.

		 -->

		<property name="hibernate.hbm2ddl.auto">update</property>

		<!-- 引入orm元数据

			路径书写: 填写src下的路径

		 -->

		<mapping resource="club/dohacker/entity/Course.hbm.xml" />

		<mapping resource="club/dohacker/entity/FileInfo.hbm.xml" />

		<mapping resource="club/dohacker/entity/Student.hbm.xml" />

		<mapping resource="club/dohacker/entity/Teacher.hbm.xml" />

		<mapping resource="club/dohacker/entity/Department.hbm.xml" />

		<mapping resource="club/dohacker/entity/StudentCourseInfo.hbm.xml" />

		<mapping resource="club/dohacker/entity/Class.hbm.xml" />

	</session-factory>

</hibernate-configuration>

2.HibernateUtils类如下:

public class HibernateUtils {

	private static SessionFactory sf;

	

	static{

		Configuration conf = new Configuration().configure();

		sf = conf.buildSessionFactory();

	}

	

	public static Session openSession(){

				Session session = sf.openSession();

				return session;

	}

	

	public static Session getCurrentSession(){

		Session session = sf.getCurrentSession();

		

		return session;

	}

	public static void main(String[] args) {

		System.out.println(HibernateUtils.openSession());

	}

	

}

问题是每当走到 sf = conf.buildSessionFactory(); 这一行代码的时候就发生错误了 , 我重新建立了orm文件 , 之前没有发生过错误 , 重写了orm文件后多就发生了这种错误 , 望高人指点一下 ， 百度也没有找到原因 :

org.hibernate.boot.model.naming.IllegalIdentifierException: Identifier text cannot be null

	at org.hibernate.boot.model.naming.Identifier.<init>(Identifier.java:107)

	at org.hibernate.boot.model.naming.Identifier.toIdentifier(Identifier.java:46)

	at org.hibernate.engine.jdbc.env.internal.NormalizingIdentifierHelperImpl.toIdentifier(NormalizingIdentifierHelperImpl.java:83)

	at org.hibernate.boot.model.relational.Database.toIdentifier(Database.java:104)

	at org.hibernate.boot.model.source.internal.hbm.RelationalObjectBinder.bindColumn(RelationalObjectBinder.java:116)

	at org.hibernate.boot.model.source.internal.hbm.RelationalObjectBinder.bindColumnsAndFormulas(RelationalObjectBinder.java:87)

	at org.hibernate.boot.model.source.internal.hbm.ModelBinder$AbstractPluralAttributeSecondPass.bindCollectionKey(ModelBinder.java:3277)

	at org.hibernate.boot.model.source.internal.hbm.ModelBinder$AbstractPluralAttributeSecondPass.doSecondPass(ModelBinder.java:3078)

	at org.hibernate.boot.internal.InFlightMetadataCollectorImpl.processSecondPasses(InFlightMetadataCollectorImpl.java:1655)

	at org.hibernate.boot.internal.InFlightMetadataCollectorImpl.processSecondPasses(InFlightMetadataCollectorImpl.java:1623)

	at org.hibernate.boot.model.process.spi.MetadataBuildingProcess.complete(MetadataBuildingProcess.java:278)

	at org.hibernate.boot.model.process.spi.MetadataBuildingProcess.build(MetadataBuildingProcess.java:83)

	at org.hibernate.boot.internal.MetadataBuilderImpl.build(MetadataBuilderImpl.java:418)

	at org.hibernate.boot.internal.MetadataBuilderImpl.build(MetadataBuilderImpl.java:87)

	at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:692)

	at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:724)

	at club.dohacker.utils.HibernateUtils.<clinit>(HibernateUtils.java:14)

	at club.dohacker.filter.SessionFilter.doFilter(SessionFilter.java:34)

	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)

	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)

	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:240)

	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:164)

	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:462)

	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:164)

	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)

	at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:563)

	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)

	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:399)

	at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:317)

	at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:204)

	at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:182)

	at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:311)

	at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)

	at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)

	at java.lang.Thread.run(Unknown Source)