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....】