buildSessionFactory()是出错

大家帮我看看，是什么错误<?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"><hibernate-configuration>    <session-factory>        <!-- Database connection settings -->
        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="connection.url">jdbc:mysql://localhost/student</property>
        <property name="connection.username">root</property>
        <property name="connection.password">kaixin</property>        <!-- SQL dialect -->
        <property name="dialect">org.hibernate.dialect.MySQLInnoDBDialect</property>        <!-- Echo all executed SQL to stdout -->
        <property name="show_sql">true</property>
        <mapping resource="com/student/hibernate/module/student.hbm.xml"/>    </session-factory></hibernate-configuration>
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.student.hibernate.module">
  <class name="Student" table="tb_user">
      <id name="userid">
         <generator class="idnetity"></generator>
      </id>
      <property name="password" type="string"></property>
      <property name="username" type="string"></property>
      <property name="email" type="string"></property>
    
  </class>
</hibernate-mapping>public void addstudent(String username,String password,String email) {
 Configuration config=new Configuration().configure();
  
   SessionFactory sfFactory=config.buildSessionFactory();
   Session sess=sfFactory.openSession();
   Transaction txTransaction=sess.beginTransaction();
   
   Student s=new Student();
   
   s.setEmail(email);
   s.setEmail(password);
   s.setUsername(username);
   
   sess.save(s);
   txTransaction.commit();
   sess.close();
   sfFactory.close();
}错误报告
root causejava.lang.NoClassDefFoundError: net/sf/ehcache/CacheException
java.lang.Class.getDeclaredConstructors0(Native Method)
java.lang.Class.privateGetDeclaredConstructors(Unknown Source)
java.lang.Class.getConstructor0(Unknown Source)
java.lang.Class.newInstance0(Unknown Source)
java.lang.Class.newInstance(Unknown Source)
org.hibernate.cfg.SettingsFactory.createCacheProvider(SettingsFactory.java:327)
org.hibernate.cfg.SettingsFactory.buildSettings(SettingsFactory.java:219)
org.hibernate.cfg.Configuration.buildSettings(Configuration.java:1881)
org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1174)
com.student.common.studentmanger.addstudent(studentmanger.java:11)
com.student.servlet.AddStudentServlet.doPost(AddStudentServlet.java:47)
javax.servlet.http.HttpServlet.service(HttpServlet.java:641)
javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
root causejava.lang.ClassNotFoundException: net.sf.ehcache.CacheException
org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1711)
org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1556)
java.lang.Class.getDeclaredConstructors0(Native Method)
java.lang.Class.privateGetDeclaredConstructors(Unknown Source)
java.lang.Class.getConstructor0(Unknown Source)
java.lang.Class.newInstance0(Unknown Source)
java.lang.Class.newInstance(Unknown Source)
org.hibernate.cfg.SettingsFactory.createCacheProvider(SettingsFactory.java:327)
org.hibernate.cfg.SettingsFactory.buildSettings(SettingsFactory.java:219)
org.hibernate.cfg.Configuration.buildSettings(Configuration.java:1881)
org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1174)
com.student.common.studentmanger.addstudent(studentmanger.java:11)
com.student.servlet.AddStudentServlet.doPost(AddStudentServlet.java:47)
javax.servlet.http.HttpServlet.service(HttpServlet.java:641)
javax.servlet.http.HttpServlet.service(HttpServlet.java:722)