@MapperScan注解

@MapperScan("路径")
@SpringBootApplication
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(OrderApplication.class, args);
    }
}

@MapperScan
在springboot项目中会自动扫描你写的mapper接口并创建实现类
所以你不需要每一个mapper接口都加上一个@mapper

        org.mybatis.spring.boot
       mybatis-spring-boot-starter

package cn.itcast.order;

import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;

@MapperScan("cn.itcast.order.mapper")
@SpringBootApplication
public class OrderApplication {

    public static void main(String[] args) {
        SpringApplication.run(OrderApplication.class, args);
    }
}

package cn.itcast.order.mapper;

import cn.itcast.order.pojo.Order;
import org.apache.ibatis.annotations.Select;

public interface OrderMapper  {

    @Select("select * from tb_order where id = #{id}")
    Order findById(Long id);
}