spring NotWritablePropertyException异常

Caused by: org.springframework.beans.NotWritablePropertyException: Invalid property 'userDao' of bean class [tarena.service.UserServiceImpl]: Bean property 'userDao' is not writable or has an invalid setter method. Does the parameter type of the setter match the return type of the getter?at org.springframework.beans.BeanWrapperImpl.setPropertyValue(BeanWrapperImpl.java:801)at org.springframework.beans.BeanWrapperImpl.setPropertyValue(BeanWrapperImpl.java:651)at org.springframework.beans.AbstractPropertyAccessor.setPropertyValues(AbstractPropertyAccessor.java:78)at org.springframework.beans.AbstractPropertyAccessor.setPropertyValues(AbstractPropertyAccessor.java:59)at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1276)... 16 more