hibernate中SessionFactory获取问题

Question

public class HibernateUtil {
	private static SessionFactory sessionFactory;
	private static Session session;
	static {
		//创建configuration对象，读取hibernate.cfg.xml文件，完成初始化
		Configuration config = new Configuration().configure();
		ServiceRegistry serviceRegistry = new ServiceRegistryBuilder().applySettings(config.getProperties()).buildServiceRegistry();
		sessionFactory = config.buildSessionFactory(serviceRegistry);            //16
		
	}
	
	//获取sessionFactory
	public static SessionFactory getSessionFactory() {
		return sessionFactory;
	}
	
	//获取session对象
	public static Session getSession() {
		session = sessionFactory.openSession();
		return session;
	}
	
	//关闭会话
	public static void closeSession(Session session) {
		if(session!=null) {
			session.close();
		}
	}
	
}
public class Test {

	public static void main(String[] args) {
		add();                                                                //14
	}
	
	//将学生添加到班级
	public static void add() 
	{
		Grade g = new Grade("java一班", "java软件开发一班");
		Student s1 = new Student("张三", "男");
		Student s2 = new Student("慕女神","女");
		
		g.getStudents().add(s1);
		g.getStudents().add(s2);
		
		//保存班级、学生信息
		Session session = HibernateUtil.getSession();                    //29
		Transaction transaction = session.beginTransaction();
		session.save(g);
		session.save(s1);
		session.save(s2);
		transaction.commit();
		HibernateUtil.closeSession(session);
	}
}
错误信息：
Exception in thread "main" java.lang.ExceptionInInitializerError
	at com.imooc.entity.Test.add(Test.java:29)
	at com.imooc.entity.Test.main(Test.java:14)
Caused by: org.hibernate.MappingException: Could not get constructor for org.hibernate.persister.entity.SingleTableEntityPersister
	at org.hibernate.persister.internal.PersisterFactoryImpl.create(PersisterFactoryImpl.java:185)
	at org.hibernate.persister.internal.PersisterFactoryImpl.createEntityPersister(PersisterFactoryImpl.java:135)
	at org.hibernate.internal.SessionFactoryImpl.<init>(SessionFactoryImpl.java:385)
	at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1790)
	at com.imooc.util.HibernateUtil.<clinit>(HibernateUtil.java:16)
	... 2 more
Caused by: org.hibernate.HibernateException: Unable to instantiate default tuplizer [org.hibernate.tuple.entity.PojoEntityTuplizer]
	at org.hibernate.tuple.entity.EntityTuplizerFactory.constructTuplizer(EntityTuplizerFactory.java:138)
	at org.hibernate.tuple.entity.EntityTuplizerFactory.constructDefaultTuplizer(EntityTuplizerFactory.java:188)
	at org.hibernate.tuple.entity.EntityMetamodel.<init>(EntityMetamodel.java:341)
	at org.hibernate.persister.entity.AbstractEntityPersister.<init>(AbstractEntityPersister.java:507)
	at org.hibernate.persister.entity.SingleTableEntityPersister.<init>(SingleTableEntityPersister.java:146)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
	at java.lang.reflect.Constructor.newInstance(Unknown Source)
	at org.hibernate.persister.internal.PersisterFactoryImpl.create(PersisterFactoryImpl.java:163)
	... 6 more
Caused by: java.lang.reflect.InvocationTargetException
	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
	at java.lang.reflect.Constructor.newInstance(Unknown Source)
	at org.hibernate.tuple.entity.EntityTuplizerFactory.constructTuplizer(EntityTuplizerFactory.java:135)
	... 15 more
Caused by: org.hibernate.PropertyNotFoundException: Could not find a getter for student in class com.imooc.entity.Grade
	at org.hibernate.property.BasicPropertyAccessor.createGetter(BasicPropertyAccessor.java:316)
	at org.hibernate.property.BasicPropertyAccessor.getGetter(BasicPropertyAccessor.java:310)
	at org.hibernate.mapping.Property.getGetter(Property.java:321)
	at org.hibernate.tuple.entity.PojoEntityTuplizer.buildPropertyGetter(PojoEntityTuplizer.java:444)
	at org.hibernate.tuple.entity.AbstractEntityTuplizer.<init>(AbstractEntityTuplizer.java:200)
	at org.hibernate.tuple.entity.PojoEntityTuplizer.<init>(PojoEntityTuplizer.java:82)
	... 20 more

看不出哪出问题了，求解啊！！！

Answer 1

 Could not find a getter for student in class com.imooc.entity.Grade。