Initial SessionFactory creation failedorg.hibernate.AnnotationException:解决方案

Initial SessionFactory creation failedorg.hibernate.AnnotationException:
刚写的报错：
Initial SessionFactory creation failedorg.hibernate.AnnotationException: mappedBy reference an unknown target entity property: com.super120.Model.Operation.oper in com.super120.Model.Operation.operations
用的hibernate3.6.10
hibernateUtils类

public class HibernateUtils {

	private static final SessionFactory sessionFactory;

	static {
		try {
			Configuration cfg = new Configuration();
			sessionFactory = cfg.configure().buildSessionFactory();
		} catch (Throwable e) {
			System.err.println("Initial SessionFactory creation failed" + e);
			throw new ExceptionInInitializerError(e);
		}
	}

	public static SessionFactory getSessionFactory() {
		return sessionFactory;
	}

	public static Session getSession() {
		return sessionFactory.openSession();
	}

	public static void closeSession(Session session) throws HibernateException {
		if (session != null) {
			if (session.isOpen()) {
				session.close();
			}
		}
	}

	public static void rollback(Transaction tran) {
		try {
			if (tran != null) {
				tran.rollback();
			}
		} catch (HibernateException he) {
			System.out.println("Rollback faild." + he);
		}
	}
}

operation类:

package com.super120.Model;

import java.util.HashSet;
import java.util.Set;

import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;

@Entity
@Table(name="tb_Operation")
public class Operation {
	private int ID;
	
	private String OperationName;
	
	private String Description;
	
	private String Reserved;
	
	private Set<Operation> operations = new HashSet<Operation>();
	

	
	@Id
	@GeneratedValue(strategy = GenerationType.AUTO)
	public int getID() {
		return ID;
	}

	public void setID(int iD) {
		ID = iD;
	}

	
	
	@OneToMany(cascade={CascadeType.REMOVE},fetch=FetchType.EAGER,mappedBy="oper")
	public Set<Operation> getOperations() {
		return operations;
	}

	public void setOperations(Set<Operation> operations) {
		this.operations = operations;
	}

	
	public String getOperationName() {
		return OperationName;
	}

	public void setOperationName(String operationName) {
		OperationName = operationName;
	}

	public String getDescription() {
		return Description;
	}

	public void setDescription(String description) {
		Description = description;
	}

	public String getReserved() {
		return Reserved;