hibernate小问题

log4j:WARN No appenders could be found for logger (org.hibernate.cfg.Environment).
log4j:WARN Please initialize the log4j system properly.
Exception in thread "main" java.lang.NoClassDefFoundError: students/student (wrong name: students/Student)
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(Unknown Source)
at java.security.SecureClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.access$100(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClassInternal(Unknown Source)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at org.hibernate.util.ReflectHelper.classForName(ReflectHelper.java:100)
at org.hibernate.util.ReflectHelper.reflectedPropertyClass(ReflectHelper.java:70)
at org.hibernate.mapping.SimpleValue.setTypeUsingReflection(SimpleValue.java:276)
at org.hibernate.cfg.HbmBinder.bindSimpleId(HbmBinder.java:401)
at org.hibernate.cfg.HbmBinder.bindRootPersistentClassCommonValues(HbmBinder.java:334)
at org.hibernate.cfg.HbmBinder.bindRootClass(HbmBinder.java:273)
at org.hibernate.cfg.HbmBinder.bindRoot(HbmBinder.java:144)
at org.hibernate.cfg.Configuration.add(Configuration.java:669)
at org.hibernate.cfg.Configuration.addInputStream(Configuration.java:504)
at org.hibernate.cfg.Configuration.addResource(Configuration.java:566)
at org.hibernate.cfg.Configuration.parseMappingElement(Configuration.java:1587)
at org.hibernate.cfg.Configuration.parseSessionFactory(Configuration.java:1555)
at org.hibernate.cfg.Configuration.doConfigure(Configuration.java:1534)
at org.hibernate.cfg.Configuration.doConfigure(Configuration.java:1508)
at org.hibernate.cfg.Configuration.configure(Configuration.java:1428)
at org.hibernate.cfg.Configuration.configure(Configuration.java:1414)
at students.Show.main(Show.java:17)
hibernate.cfg.xml文件代码<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
                    "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
                    "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd"><!-- Generated by MyEclipse Hibernate Tools.                                     -->
<hibernate-configuration><session-factory>
  <property name="hibernate.hbm2ddl.auto">update</property>
  <property name="dialect">
    org.hibernate.dialect.SQLServerDialect
  </property>
  <property name="connection.url">jdbc:sqlserver://localhost:1433;databaseName=pets
  </property>
  <property name="connection.username">sa</property>
  <property name="connection.password">123</property>
  <property name="connection.driver_class">com.microsoft.sqlserver.jdbc.SQLServerDriver
  </property>
  <property name="show_sql">true</property>
  <mapping resource="Students/Student.hbm.xml"/></session-factory></hibernate-configuration>
Students.hbm.xml这个文件在students包中
这个是Students.hbm.xml中的代码
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
                                                                     "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!--    This mapping demonstrates the use of
    the EJB3 compliant table hilo generator-->
<hibernate-mapping package="students">
<class name="student" table="userinfo">
    <id name="id">
     <generator class="native"/>
    </id>
    <property name="username"/>
    <property name="password"/>
</class>
</hibernate-mapping>