MyBatis-Spring包自动扫描MyBatis Mapper接口并将其注册为Spring Bean

学习spring整合mybatis时，写SQL语句的Mapper接口明明没有任何被spring接管的痕迹（前面没有注解）但在serviceimpl类中却可以被自动装载。

BookDao.java（mapper接口类）：

package com.itheima.dao;

import com.itheima.domain.Book;
import org.apache.ibatis.annotations.Delete;
import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.Select;
import org.apache.ibatis.annotations.Update;

import java.util.List;

public interface BookDao {

//    @Insert("insert into tbl_book values(null,#{type},#{name},#{description})")
    @Insert("insert into tbl_book (type,name,description) values(#{type},#{name},#{description})")
    public void save(Book book);

    @Update("update tbl_book set type = #{type}, name = #{name}, description = #{description} where id = #{id}")
    public void update(Book book);

    @Delete("delete from tbl_book where id = #{id}")
    public void delete(Integer id);

    @Select("select * from tbl_book where id = #{id}")
    public Book getById(Integer id);

    @Select("select * from tbl_book")
    public List<Book> getAll();
}

BookServiceImpl.java（业务层实现类）：

package com.itheima.service.impl;

import com.itheima.dao.BookDao;
import com.itheima.domain.Book;
import com.itheima.service.BookService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.List;

@Service
public class BookServiceImpl implements BookService {
    @Autowired
    private BookDao bookDao;

    public boolean save(Book book) {
        bookDao.save(book);
        return true;
    }

    public boolean update(Book book) {
        bookDao.update(book);
        return true;
    }

    public boolean delete(Integer id) {
        bookDao.delete(id);
        return true;
    }

    public Book getById(Integer id) {
        return bookDao.getById(id);
    }

    public List<Book> getAll() {
        return bookDao.getAll();
    }
}

这是因为之前引入的包MyBatis-Spring，默认会扫描整个项目中指定的包及其子包下的所有Mapper接口，并将其注册为Spring Bean。（MyBatis-Spring-Boot-Starter包也有相同功能）这个扫描范围是可以配置的，通过设置MapperScannerConfigurer的basePackage属性来指定要扫描的包。

若是在配置类里设置扫描范围，有两种写法，第一种是写在注解上：

@Configuration
@MapperScan("com.example.dao")
public class MyBatisConfig {
    // 其他配置
}

第二种是定义实体bean：

package com.itheima.config;

import org.mybatis.spring.SqlSessionFactoryBean;
import org.mybatis.spring.mapper.MapperScannerConfigurer;
import org.springframework.context.annotation.Bean;
import javax.sql.DataSource;

public class MyBatisConfig {

    @Bean
    public MapperScannerConfigurer mapperScannerConfigurer(){
        MapperScannerConfigurer msc = new MapperScannerConfigurer();
        msc.setBasePackage("com.itheima.dao");
        return msc;
    }
//其他配置

}