CatalogDao中方法参数的疑问

以下是CatalogDao.java代码，其中最后一个方法（ List<Catalog> selectByPid(int pid);）的参数在业务层是

如何拿到的，业务层并没有显示调用该方法。请详细解释一下该方法的执行机制，谢谢！

package com.imooc.icake.dao;

import com.imooc.icake.entity.Catalog;
import org.apache.ibatis.annotations.*;

import java.util.List;

public interface CatalogDao {
   @Insert("<script>" +
           "insert catalog(title,pid,info) values"+
           "<foreach collection='list' item='catalog' separator=',' >" +
           "(#{catalog.title},#{catalog.pid},#{catalog.info})"+
           "</foreach>"+
           "</script>")
   @Options(useGeneratedKeys = true,keyProperty = "id")
   void batchInsert(List<Catalog> list);

   @Delete("delete from catalog where id=#{id}")
   void delete(int id);

   @Select("select * from catalog where id=#{id}")
   @Results(id = "all",value = {
           @Result(column = "id",property ="id",id = true),
           @Result(column = "title",property = "title"),
           @Result(column = "pid",property = "pid"),
           @Result(column = "info",property = "info"),
           @Result(column = "id",property = "children",many=@Many(select = "selectByPid") )

})
   Catalog select(int id);

   @Select("select * from catalog where pid=#{pid}")
   @ResultMap("all")
   List<Catalog> selectByPid(int pid);
}