配置applicationContext.xml出错

-- 添加 -->     <!-- 配置业务层的类 -->             <bean id="addService" class="com.zhang.service.addService">     <property name="addDao" ref="addDao"></property>    </bean>                                           <!-- 配置Dao的类 -->                                      <bean id="addDao" class="com.zhang.dao.addDao">   
报错了
         </bean>Error setting property values; nested exception is org.springframework.beans.NotWritablePropertyException: Invalid property 'addDao' of bean class [com.zhang.service.addService]: Bean property 'addDao' is not writable or has an invalid setter method. Did you mean 'adao'?