create table `t_dict_district` (
  `id` int (11) NOT NULL AUTO_INCREMENT,
  `parent` varchar (6) DEFAULT NULL,
  `code` varchar (6) DEFAULT NULL,
  `name` varchar (16) DEFAULT NULL,
     PRIMARY KEY (`id`)
);
insert into `t_dict_district` (`id`, `parent`, `code`, `name`) values('1','110100','110101','东城区');
insert into `t_dict_district` (`id`, `parent`, `code`, `name`) values('2','110100','110102','西城区');
insert into `t_dict_district` (`id`, `parent`, `code`, `name`) values('3','110100','110103','崇文区');
insert into `t_dict_district` (`id`, `parent`, `code`, `name`) values('4','110100','110104','宣武区');
insert into `t_dict_district` (`id`, `parent`, `code`, `name`) values('5','110100','110105','朝阳区');

package com.cy.store.entity;
import java.io.Serializable;
import java.util.Objects;
/** 省/市/区数据的实体类 */
public class District implements Serializable {
    private Integer id;
    private String parent;
    private String code;
    private String name;

select * from t_dict_district where parent =? order by code ASC

package com.cy.store.mapper;
import com.cy.store.entity.District;
import java.util.List;
public class DistrictMapper {
    /**
     * 根据父代号查询信息
     * @param parent 父代号
     * @return 某个父区域下的所有区域列表
     */
    List<District> findByParent(Integer parent);
}

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.cy.store.mapper.DistrictMapper">
    <!-- 获取全国所有省/某省所有市/某市所有区：List<District> findByParent(String parent) -->
    <select id="findByParent" resultType="com.cy.store.entity.District">
        SELECT * FROM t_dict_district WHERE parent=#{parent} ORDER BY code ASC
    </select>
</mapper>

 @Autowired
    private DistrictMapper districtMapper;
    @Test
    public void findByParent(){
        List<District> list = districtMapper.findByParent("110100");
        for (District d:list) {
            System.out.println(d);
        }
    }

package com.cy.store.service;
import com.cy.store.entity.District;
import java.util.List;
public interface IDistrictService {
    /**
     * 根据父代号来查询区域的信息(省市区)
     * @param parent 父代号
     * @return 多个区域信息
     */
    List<District> getParent(String parent);
}

package com.cy.store.service.impl;
import com.cy.store.entity.District;
import com.cy.store.mapper.DistrictMapper;
import com.cy.store.service.IDistrictService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import java.util.List;
@Service
public class DistrictServiceImpl implements IDistrictService {
    @Autowired
    private DistrictMapper districtMapper;
    @Override
    public List<District> getParent(String parent) {
        List<District> list = districtMapper.findByParent(parent);
        /**
         * 在进行网络数据传输时，为了尽量避免无效的数据传递，可以将无效数据设置为null
         * 可以节省流量，另一方面提升了效率
         */
        for (District d:list) {
            d.setId(null);
            d.setParent(null);
        }
        return list;
    }
}

package com.cy.store.service;
import com.cy.store.entity.Address;
import com.cy.store.entity.District;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.yaml.snakeyaml.events.Event;
import java.util.List;
//@SpringBootTest：表示标注当前的类是测试类，不会随同项目一块打包
@SpringBootTest
//@RunWith：表示启动这个单元测试类（单元测试类是不能够运行的），需要传递一个参数，必须是SpringRunner的实例类型
//@RunWith(SpringRunner.class)
public class DistrictServiceTests {
    @Autowired
    private IDistrictService districtService;
    @Test
    public void getParent(){
        List<District> list = districtService.getParent("86");
        for (District d : list) {
            System.err.println(d);
        }
    }
}

/districts/
GET 
String parent
JsonResult<List<District>>

package com.cy.store.controller;
import com.cy.store.entity.District;
import com.cy.store.service.IDistrictService;
import com.cy.store.util.JsonResult;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import java.util.List;
@RestController
@RequestMapping("districts")
public class DistrictController extends BaseController {
    @Autowired
    private IDistrictService districtService;
    //凡是districts开头的请求都被拦截到getByParent()方法
    @RequestMapping({"/",""})
    public JsonResult<List<District>> getByParent(String parent){
        List<District> data = districtService.getParent(parent);
        return new JsonResult<>(OK,data);
    }
}

patterns.add("/districts/**");

<!--    <script type="text/javascript" src="../js/distpicker.data.js"></script>-->
<!--    <script type="text/javascript" src="../js/distpicker.js"></script>-->