Hibernate创建映射文件时not found while looking for property错误

最近在研究Hibernate。过程当中碰到了很多问题啊！其中一个就是not found while looking for property错误

Caused by: org.hibernate.MappingException: class main.java.POJO.User not found while looking for property: id

配置文件如下：

<?xml version="1.0"?>  
<!DOCTYPE hibernate-mapping PUBLIC   
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"  
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">      
<hibernate-mapping>   
    <class name="entity/Employee" table="employee">
        <id name="eid" column="eid">
            <generator class="native"></generator>
        </id>
        <property name="ename" column="ename" length="20"></property>
        <property name="sex" column="sex" length="20"></property>
        <property name="birthday" column="birthday"></property>
        <property name="joinDate" column="joinDate"></property>
        <property name="eno" column="eno" length="20"></property>
        <property name="username" column="username" length="20"></property>
        <property name="password" column="password" length="20"></property>

        <!-- 关联关系映射(name为类中对应的属性) -->
        <many-to-one name="department" class="entity.Department" column="did"></many-to-one>
    </class>
</hibernate-mapping>  

怎么看配置也没有问题啊！网上找了N久！终于在这篇文章里面看到了原因！
按照里面的方法把每个值都加上属性后就OK了

<?xml version="1.0"?>  
<!DOCTYPE hibernate-mapping PUBLIC   
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"  
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">      
<hibernate-mapping>   
    <class name="entity/Employee" table="employee">
        <id name="eid" column="eid" type="java.lang.Integer">
            <generator class="native"></generator>
        </id>
        <property name="ename" column="ename" length="20" type="java.lang.String"></property>
        <property name="sex" column="sex" length="20" type="java.lang.String"></property>
        <property name="birthday" column="birthday" type="java.util.Date"></property>
        <property name="joinDate" column="joinDate" type="java.util.Date"></property>
        <property name="eno" column="eno" length="20" type="java.lang.String"></property>
        <property name="username" column="username" length="20" type="java.lang.String"></property>
        <property name="password" column="password" length="20" type="java.lang.String"></property>

        <!-- 关联关系映射(name为类中对应的属性) -->
        <many-to-one name="department" class="entity.Department" column="did"></many-to-one>
    </class>
</hibernate-mapping>