Spring mvc 报错：No qualifying bean of type [java.lang.String] found for dependency:

具体错误：

No qualifying bean of type [java.lang.String] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {}

原因:

1.对应要注入的实现类没有 加注解，如dao层 @Repository 如service层 @Service

2."You generally autowire to your interface type and not impl."调用的接口是否有具体的实现类。

3.@Autowired下面，没有类，直接跟了@RequestMapping。【我报错的原因。无语....】