ssm錯誤dDependencyException: Error creating bean with name 'userController': Unsatisfied dependency expressed through field 'userService';

dDependencyException: Error creating bean with name 'userController': Unsatisfied dependency expressed through field 'userService'; 
nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: 
No qualifying bean of type 'com.bjpowernode.blog.back.service.UserService' 
available: expected at least 1 bean which qualifies as autowire candidate.
 Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}

原因：service層的注解沒有寫

解決辦法

檢查 dao層（@param可不寫）

service層（@Server） 

controller層（@Controller）