Consider defining a bean of type 'app.mapper.UserMapper' in your configuration.

バグの内容:
Description:Parameter 0 of constructor in app.controller.IndexControllerMaYi required a bean of type 'app.mapper.UserMapper' that could not be found.Action:Consider defining a bean of type 'app.mapper.UserMapper' in your configuration.
解決策
mainメソッドに追加

@MapperScan({"app.mapper","app.test01.dao","app.test02.dao"})

// *******

package app;

import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.ComponentScan;

@ComponentScan(basePackages = "app")
@MapperScan({"app.mapper","app.test01.dao","app.test02.dao"})      
@SpringBootApplication // 
public class BooklistApplication {// ， 

   public static void main(String[] args) {

      SpringApplication.run(BooklistApplication.class, args);// 
      System.out.println("main...");
   }
}

まとめ:
@SpringBootApplicatoin=@Configuration+@EnableAutoConfiguration+@ComponentScan
@SpringBootApplicatoinは@ComponentScanでスキャンされ、@Component、@Controller、@Service、@Repositoryなどを含むComponentでスキャンされます
Mybatisの自動スキャン構成では、注記構成を使用する場合、@MapperScanでスキャンする必要があるMapperの位置を構成すれば、ほとんどの場合、ニーズを満たします.