JPA字段映射问题

在mysql里面建了一个表

mysql> show columns from file_items;
+-----------+--------------+------+-----+---------+----------------+
| Field     | Type         | Null | Key | Default | Extra          |
+-----------+--------------+------+-----+---------+----------------+
| id        | int(11)      | NO   | PRI | NULL    | auto_increment |
| item_name | varchar(100) | YES  |     | NULL    |                |
+-----------+--------------+------+-----+---------+----------------+
2 rows in set (0.03 sec)

jpa的映射类为

@Entity
@Table(name = "file_items")
public class ItemFile {
	private int id;
	private String itemName;
	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	@Column(name="item_name")
	public String getItemName() {
		return itemName;
	}
	public void setItemName(String itemname) {
		this.itemName = itemname;
	}


}

在tomcat项目启动的时候报错：

Caused by: org.hibernate.MappingException: Could not determine type for: com.nbrc.model.ItemFile, for columns: [org.hibernate.mapping.Column(filename)]
	at org.hibernate.mapping.SimpleValue.getType(SimpleValue.java:266)
	at org.hibernate.mapping.SimpleValue.isValid(SimpleValue.java:253)
	at org.hibernate.mapping.Property.isValid(Property.java:185)
	at org.hibernate.mapping.PersistentClass.validate(PersistentClass.java:440)
	at org.hibernate.mapping.RootClass.validate(RootClass.java:192)
	at org.hibernate.cfg.Configuration.validate(Configuration.java:1102)
	at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1287)
	at org.hibernate.cfg.AnnotationConfiguration.buildSessionFactory(AnnotationConfiguration.java:915)
	at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:730)

其他的类都没有问题，可能又是一个新手问题，不管非常郁闷，不知道错在哪里，不过原来的item_name这列的名字是叫filename，我看报这个错，改过来的，请问各位高手是什么原因了