因为这种注入方式存在缺陷,springboot不建议使用这种方式。可以采用构造方法的方式来注入

修改前：

@RestController
public class UserController {

    @Autowired
    UserMapper userMapper;

    @RequestMapping("/select")
    public String select(){
        return userMapper.selectAll().toString();
    }
}

 

修改后：

@RestController
public class UserController {

    final UserMapper userMapper;

    public UserController(UserMapper userMapper){
        this.userMapper = userMapper;
    }

    @RequestMapping("/select")
    public String select(){
        return userMapper.selectAll().toString();
    }
}