一，数据源
1.1，数据库查出来的数据是
两张表先各自左外连接，然后在相互左外连接查找省市县的数据（业务需求必须这样做，省市去的是第一张表，而市县取的是第二张表，两张表中间通过市的名字连接）见这个博文的最后一张图片
1.2，要求转换成的json格式的数据
1.2.1，完整数据
json省市县数据源（这是全部的数据）
1.2.2，抽取的数据
[
{
"Code": "410000",
"Name": "河南省",
"level": [
{
"Code": "414500",
"Name": "郑州市",
"level": [
{
"Code": "414500",
"Name": "二七区",
"sort": 1
},
{
"Code": "414500",
"Name": "中原区",
"sort": 2
}
],
"sort": 1
},
{
"Code": "414530",
"Name": "新乡市",
"level": [
{
"Code": "414530",
"Name": "卫滨区",
"sort": 1
},
{
"Code": "414530",
"Name": "牧野区",
"sort": 2
}
],
"sort": 2
}
]
},
{
"Code": "410000",
"Name": "陕西省",
"level": [
{
"Code": "414500",
"Name": "汉中市",
"level": [
{
"Code": "414500",
"Name": "西乡县",
"sort": 1
},
{
"Code": "414500",
"Name": "南郑县",
"sort": 2
}
],
"sort": 1
},
{
"Code": "414530",
"Name": "宝鸡市",
"level": [
{
"Code": "414530",
"Name": "岐山县",
"sort": 1
},
{
"Code": "414530",
"Name": "芙蓉县",
"sort": 2
}
],
"sort": 2
}
]
}
]
二，转化的整体代码
2.1，代码总览
/**
* 查询省份城市区县
*
* @return
*/
public String queryFullZoneInfo() {
List<Map<String, String>> mapList = zoneInfoService.queryFullZoneInfo();
List<Map<String, Object>> zoneList = new ArrayList<Map<String, Object>>();
Map<String, Object> existMap = new HashMap<String, Object>();
for (Map<String, String> map : mapList) {
String province = map.get("province");
Map<String, Object> provinceMap = null;
if (existMap.containsKey(province)) {
provinceMap = (Map<String, Object>) existMap.get(province);
} else {
provinceMap = new HashMap<String, Object>();
existMap.put(province, provinceMap);
zoneList.add(provinceMap);
}
provinceMap.put("Code", map.get("provinceCode"));
provinceMap.put("Name", map.get("province"));
String city = map.get("city");
if (StringUtils.isNotEmpty(city)) {
List<Map<String, Object>> provinceCityList = null;
if (existMap.containsKey(province + "_")) {
provinceCityList = (List<Map<String, Object>>) existMap.get(province + "_");
} else {
provinceCityList = new ArrayList<Map<String, Object>>();
existMap.put(province + "_", provinceCityList);
provinceMap.put("level", provinceCityList);
}
Map<String, Object> provinceCityMap = null;
if (existMap.containsKey(province + "_" + city)) {
provinceCityMap = (Map<String, Object>) existMap.get(province + "_" + city);
} else {
provinceCityMap = new HashMap<String, Object>();
existMap.put(province + "_" + city, provinceCityMap);
provinceCityList.add(provinceCityMap);
String citySort = String.valueOf(existMap.get(province + "_sort"));
existMap.put(province + "_sort", "null".equals(citySort) ? 1 : NumberUtils.toInt(citySort) + 1);
provinceCityMap.put("sort", existMap.get(province + "_sort"));
}
provinceCityMap.put("Name", city);
provinceCityMap.put("Code", map.get("cityCode"));
List<Map<String, Object>> provinceCityCountryList = null;
if (existMap.containsKey(province + "_" + city + "_")) {
provinceCityCountryList = (List<Map<String, Object>>) existMap.get(province + "_" + city + "_");
} else {
provinceCityCountryList = new ArrayList<Map<String, Object>>();
existMap.put(province + "_" + city + "_", provinceCityCountryList);
provinceCityMap.put("level", provinceCityCountryList);
}
String country = map.get("country");
Map<String, Object> provinceCityCountryMap = null;
if (StringUtils.isNotEmpty(country)) {
if (existMap.containsKey(province + "_" + city + "_" + country)) {
provinceCityCountryMap = (Map<String, Object>) existMap.get(province + "_" + city + "_" + country);
} else {
provinceCityCountryMap = new HashMap<String, Object>();
existMap.put(province + "_" + city + "_" + country, provinceCityCountryMap);
provinceCityCountryList.add(provinceCityCountryMap);
String countrySort = String.valueOf(existMap.get(province + "_" + city + "_sort"));
existMap.put(province + "_" + city + "_sort", "null".equals(countrySort) ? 1 : NumberUtils.toInt(countrySort) + 1);
provinceCityCountryMap.put("sort", existMap.get(province + "_" + city + "_sort"));
}
provinceCityCountryMap.put("Code", map.get("countryCode"));
provinceCityCountryMap.put("Name", country);
} else {
provinceCityCountryMap = new HashMap<String, Object>();
provinceCityCountryList.add(provinceCityCountryMap);
provinceCityCountryMap.put("sort", 1);
provinceCityCountryMap.put("Code", "");
provinceCityCountryMap.put("Name", "");
}
}
}
try {
return JsonUtils.toJson(zoneList);
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
三，代码解析
3.1，json格式数据分析
从1.2.2的数据我们可以看到这个json所要求的数据是这个样子的
3.1.1，list
第一个大的list里面装的是34个省的对象组成的一个list集合。
3.1.2，map(对象)
每一个省中有code，和name的键值对，还有一个level的list集合
3.1.3，list
就是上面所说的level的集合，这个集合当中装的是每一个省里面的地级市的map对象
3.1.4，map(对象)
map对象里面有code，name的键值对，还有一个level的list集合，此外还有一个代表顺序的sort标示符
3.1.5，list
就是上面所说的level的集合，这个集合当中装的是每一个地级市里面装的县城的map对象
3.1.6，map(对象)
map对象里面有code，name的键值对，此外还有一个代表顺序的sort标示符，注意这个里面是没有list的集合了，因为它已经是最后一层了。
3.2，java代码分析
3.2.1，代码初步实现
根据上面的代码我们可以写出这样的代码
public String queryFullZoneInfo() {
List<Map<String, String>> mapList = zoneInfoService.queryFullZoneInfo();
List<Map<String, Object>> zoneList = new ArrayList<Map<String, Object>>();
Map<String, Object> existMap = new HashMap<String, Object>();
Map<String, Object> provinceMap = new HashMap<String, Object>();
Map<String, Object> provinceCityMap = new HashMap<String, Object>();
List<Map<String, Object>> provinceCityList = new ArrayList<Map<String, Object>>();
List<Map<String, Object>> provinceCityCountryList = new ArrayList<Map<String, Object>>();
Map<String, Object> provinceCityCountryMap = new HashMap<String, Object>();
for (Map<String, String> map : mapList) {
zoneList = new ArrayList<Map<String, Object>>();
provinceMap = new HashMap<String, Object>();
provinceCityMap = new HashMap<String, Object>();
provinceMap.put("Code", map.get("provinceCode"));
provinceCityList = new ArrayList<Map<String, Object>>();
provinceCityCountryList = new ArrayList<Map<String, Object>>();
provinceCityCountryMap = new HashMap<String, Object>();
provinceMap.put("Name", map.get("province"));
provinceMap.put("level", provinceCityList);
provinceCityList.add(provinceCityMap);
provinceCityMap.put("Name", map.get("city"));
provinceCityMap.put("Code", map.get("cityCode"));
provinceCityMap.put("level", provinceCityCountryList);
provinceCityCountryList.add(provinceCityCountryMap);
provinceCityCountryMap.put("Code", map.get("countryCode"));
provinceCityCountryMap.put("Name", map.get("country"));
zoneList.add(provinceMap);
}
try {
return JsonUtils.toJson(zoneList);
} catch (Exception e) {
e.printStackTrace();
}
注意上面空开的空格是和4.2做对比用的。
3.2.2，注意点
在上面的代码中虽然provinceMap是先把provinceCityList给put进去的，但是这不影响后面provinceCityList的取值，换句话就是当执行到这句
provinceMap.put("level", provinceCityList);
代码的时候，provinceCityList是null，只到这句代码
provinceCityList.add(provinceCityMap);
provinceCityMap.put("Name", map.get("city"));
provinceCityMap.put("Code", map.get("cityCode"));
执行完之后它才有的值，但同时注意了，provinceMap里面的provinceCityList也就有了值，这是后面给它赋值的。
3.2.3，注意点升级
String province = map.get("province");
Map<String, Object> provinceMap = null;
if (existMap.containsKey(province)) {
provinceMap = (Map<String, Object>) existMap.get(province);
} else {
provinceMap = new HashMap<String, Object>();
existMap.put(province, provinceMap);{黑龙江省={Name=黑龙江省, Code=230000}}
zoneList.add(provinceMap);
}
provinceMap.put("Code", map.get("provinceCode"));
provinceMap.put("Name", map.get("province"));
注意理解上面的代码：
是先申明了一个map，注意第一遍走的时候existMap.put(province, provinceMap);它是空的
但是当走到provinceMap.put("Code", map.get("provinceCode"));
provinceMap.put("Name", map.get("province"));这两行的时候它会把值给塞进去，
这时候existMap里面有值了
即使如果不走else里面的语句，也会把值给塞进去的。
3.2.4，问题点
假如像上面那样去解决问题的话，那么后面的代码永远会把前面的代码给覆盖掉的，
因为每一次都是new的一个对象。所以到最后上万条的数据，只会出来最后一条数据，
比如我测试的结果
[
{
"Code": "310000",
"Name": "上海市",
"level": [
{
"Code": "310100",
"Name": "上海市",
"level": [
{
"Code": "2909",
"Name": "长宁区"
}
]
}
]
}
]
最后返回的就是这一条数据，完全不是自己要的东西。
四，解决方法
4.1，代码
和2.1的代码是一么一样的。
4.2，注意点
这句代码就是在原来的基础上加了一个existMap的双例集合
我们把2.1的代码分开来读就会更加清晰
if (existMap.containsKey(province + "_")) {
provinceCityList = (List<Map<String, Object>>) existMap.get(province + "_");
} else {
provinceCityList = new ArrayList<Map<String, Object>>();
existMap.put(province + "_", provinceCityList);
provinceMap.put("level", provinceCityList);
}
if (existMap.containsKey(province + "_" + city)) {
provinceCityMap = (Map<String, Object>) existMap.get(province + "_" + city);
} else {
provinceCityMap = new HashMap<String, Object>();
existMap.put(province + "_" + city, provinceCityMap);
provinceCityList.add(provinceCityMap);
String citySort = String.valueOf(existMap.get(province + "_sort"));
existMap.put(province + "_sort", "null".equals(citySort) ? 1 : NumberUtils.toInt(citySort) + 1);
provinceCityMap.put("sort", existMap.get(province + "_sort"));
}
if (existMap.containsKey(province + "_" + city + "_")) {
provinceCityCountryList = (List<Map<String, Object>>) existMap.get(province + "_" + city + "_");
} else {
provinceCityCountryList = new ArrayList<Map<String, Object>>();
existMap.put(province + "_" + city + "_", provinceCityCountryList);
provinceCityMap.put("level", provinceCityCountryList);
}
if (existMap.containsKey(province + "_" + city + "_" + country)) {
provinceCityCountryMap = (Map<String, Object>) existMap.get(province + "_" + city + "_" + country);
} else {
provinceCityCountryMap = new HashMap<String, Object>();
existMap.put(province + "_" + city + "_" + country, provinceCityCountryMap);
provinceCityCountryList.add(provinceCityCountryMap);
String countrySort = String.valueOf(existMap.get(province + "_" + city + "_sort"));
existMap.put(province + "_" + city + "_sort", "null".equals(countrySort) ? 1 : NumberUtils.toInt(countrySort) + 1);
provinceCityCountryMap.put("sort", existMap.get(province + "_" + city + "_sort"));
}
4.3，解析existMap作用
因为假如现在没有这个map集合就会产生覆盖的作用，现在这个map的作用就是把取出来的值以不同的名字取出来放到map集合中来，假如下一次再去取的时候如果有就不在新建对象了，直接用原来的就行了，如果没有在建立新的对象。
这就解决了覆盖的问题。
同时也给sort排上了序号。
用下面的例子来说明
有就取原来的，没有就新建，这样的话就会把后面新的数据加到前面有的数据里面
举个例子，假如现在是河南省map1里面有name，code，和sort，leval集合，第一遍是地级市是安阳，当第二遍循环的时候，还是取省份这时候还是河南省，就不会新建一个map了，而是还是取原来的map1，这时候假如是新乡市，就会把新乡市，同样加在这个map当中，这样一个map当中就会有两个leval了
假如现在不是河南省了，而是陕西省了，就会新建一个map2，会把它里面的数据加载这个map2当中，
map1，map2装在一个list中返回，就有效的避免了第一种情况的产生了。
其中市县和上面也是同样的道理。
注意这个existMap里面装的数据会特别的多，比返回的provinceMap大了几万倍呢。
我们以上面的json的数据来手动遍历几遍。
4.3.1，首次遍历
{
"Code": "410000",
"Name": "河南省",
"level": [
{
"Code": "414500",
"Name": "郑州市",
"level": [
{
"Code": "414500",
"Name": "二七区",
"sort": 1
}
],
"sort": 1
}
]
}
4.3.2，2遍
{
"Code": "410000",
"Name": "河南省",
"level": [
{
"Code": "414500",
"Name": "郑州市",
"level": [
{
"Code": "414500",
"Name": "二七区",
"sort": 1
},
{
"Code": "414500",
"Name": "中原区",
"sort": 2
}
],
"sort": 1
}
]
}
4.3.3，3遍
{
"Code": "410000",
"Name": "河南省",
"level": [
{
"Code": "414500",
"Name": "郑州市",
"level": [
{
"Code": "414500",
"Name": "二七区",
"sort": 1
},
{
"Code": "414500",
"Name": "中原区",
"sort": 2
}
],
"sort": 1
},
{
"Code": "414530",
"Name": "新乡市",
"level": [
{
"Code": "414530",
"Name": "卫滨区",
"sort": 1
}
],
"sort": 2
}
]
}
4.3.4，4遍
{
"Code": "410000",
"Name": "河南省",
"level": [
{
"Code": "414500",
"Name": "郑州市",
"level": [
{
"Code": "414500",
"Name": "二七区",
"sort": 1
},
{
"Code": "414500",
"Name": "中原区",
"sort": 2
}
],
"sort": 1
},
{
"Code": "414530",
"Name": "新乡市",
"level": [
{
"Code": "414530",
"Name": "卫滨区",
"sort": 1
},
{
"Code": "414530",
"Name": "牧野区",
"sort": 2
}
],
"sort": 2
}
]
}
4.3.5，5遍
[
{
"Code": "410000",
"Name": "河南省",
"level": [
{
"Code": "414500",
"Name": "郑州市",
"level": [
{
"Code": "414500",
"Name": "二七区",
"sort": 1
},
{
"Code": "414500",
"Name": "中原区",
"sort": 2
}
],
"sort": 1
},
{
"Code": "414530",
"Name": "新乡市",
"level": [
{
"Code": "414530",
"Name": "卫滨区",
"sort": 1
},
{
"Code": "414530",
"Name": "牧野区",
"sort": 2
}
],
"sort": 2
}
]
},
{
"Code": "410000",
"Name": "陕西省",
"level": [
{
"Code": "414500",
"Name": "汉中市",
"level": [
{
"Code": "414500",
"Name": "西乡县",
"sort": 1
}
],
"sort": 1
}
]
}
]
4.3.6，6遍
[
{
"Code": "410000",
"Name": "河南省",
"level": [
{
"Code": "414500",
"Name": "郑州市",
"level": [
{
"Code": "414500",
"Name": "二七区",
"sort": 1
},
{
"Code": "414500",
"Name": "中原区",
"sort": 2
}
],
"sort": 1
},
{
"Code": "414530",
"Name": "新乡市",
"level": [
{
"Code": "414530",
"Name": "卫滨区",
"sort": 1
},
{
"Code": "414530",
"Name": "牧野区",
"sort": 2
}
],
"sort": 2
}
]
},
{
"Code": "410000",
"Name": "陕西省",
"level": [
{
"Code": "414500",
"Name": "汉中市",
"level": [
{
"Code": "414500",
"Name": "西乡县",
"sort": 1
},
{
"Code": "414500",
"Name": "南郑县",
"sort": 2
}
],
"sort": 1
}
]
}
]
4.3.7,7遍
[
{
"Code": "410000",
"Name": "河南省",
"level": [
{
"Code": "414500",
"Name": "郑州市",
"level": [
{
"Code": "414500",
"Name": "二七区",
"sort": 1
},
{
"Code": "414500",
"Name": "中原区",
"sort": 2
}
],
"sort": 1
},
{
"Code": "414530",
"Name": "新乡市",
"level": [
{
"Code": "414530",
"Name": "卫滨区",
"sort": 1
},
{
"Code": "414530",
"Name": "牧野区",
"sort": 2
}
],
"sort": 2
}
]
},
{
"Code": "410000",
"Name": "陕西省",
"level": [
{
"Code": "414500",
"Name": "汉中市",
"level": [
{
"Code": "414500",
"Name": "西乡县",
"sort": 1
},
{
"Code": "414500",
"Name": "南郑县",
"sort": 2
}
],
"sort": 1
},
{
"Code": "414530",
"Name": "宝鸡市",
"level": [
{
"Code": "414530",
"Name": "岐山县",
"sort": 1
}
],
"sort": 2
}
]
}
]
4.3.8,8遍
[
{
"Code": "410000",
"Name": "河南省",
"level": [
{
"Code": "414500",
"Name": "郑州市",
"level": [
{
"Code": "414500",
"Name": "二七区",
"sort": 1
},
{
"Code": "414500",
"Name": "中原区",
"sort": 2
}
],
"sort": 1
},
{
"Code": "414530",
"Name": "新乡市",
"level": [
{
"Code": "414530",
"Name": "卫滨区",
"sort": 1
},
{
"Code": "414530",
"Name": "牧野区",
"sort": 2
}
],
"sort": 2
}
]
},
{
"Code": "410000",
"Name": "陕西省",
"level": [
{
"Code": "414500",
"Name": "汉中市",
"level": [
{
"Code": "414500",
"Name": "西乡县",
"sort": 1
},
{
"Code": "414500",
"Name": "南郑县",
"sort": 2
}
],
"sort": 1
},
{
"Code": "414530",
"Name": "宝鸡市",
"level": [
{
"Code": "414530",
"Name": "岐山县",
"sort": 1
},
{
"Code": "414530",
"Name": "芙蓉县",
"sort": 2
}
],
"sort": 2
}
]
}
]
致此一个流程走完就大概知道它的一个流程了。
五，优化
5.1，优化一
因为existMap数据是特别大的，所以每当我们遍历完一个省份之后就把里面的数据清除
String province = map.get("province");
Map<String, Object> provinceMap = null;
if(province!=existMap.get("province")){
existMap.clear();
}
拿这一次的取出来的province和existMap里面的province对比，假如有就继续遍历，假如没有就说明换省份了，清空exitMap，这样会提升效率。
5.2，优化二
最后一次就不用王existMap里面放值了，因为我们知道没遍历一次省市可能一样，但是县绝对是不一样的。
String country = map.get("country");
Map<String, Object> provinceCityCountryMap = null;
if (StringUtils.isNotEmpty(country)) {
provinceCityCountryMap = new HashMap<String, Object>();
provinceCityCountryList.add(provinceCityCountryMap);
String countrySort = String.valueOf(existMap.get(province + "_" + city + "_sort"));
existMap.put(province + "_" + city + "_sort", "null".equals(countrySort) ? 1 : NumberUtils.toInt(countrySort) + 1);
provinceCityCountryMap.put("sort", existMap.get(province + "_" + city + "_sort"));
provinceCityCountryMap.put("Code", map.get("countryCode"));
provinceCityCountryMap.put("Name", country);
5.3，优化完之后完整的代码
public String queryFullZoneInfo() {
List<Map<String, String>> mapList = zoneInfoService.queryFullZoneInfo();
List<Map<String, Object>> zoneList = new ArrayList<Map<String, Object>>();
Map<String, Object> existMap = new HashMap<String, Object>();
for (Map<String, String> map : mapList) {
String province = map.get("province");
Map<String, Object> provinceMap = null;
if(province!=existMap.get("province")){
existMap.clear();
}
if (existMap.containsKey(province)) {
provinceMap = (Map<String, Object>) existMap.get(province);
} else {
provinceMap = new HashMap<String, Object>();
existMap.put(province, provinceMap);
zoneList.add(provinceMap);
}
provinceMap.put("Code", map.get("provinceCode"));
provinceMap.put("Name", map.get("province"));
String city = map.get("city");
if (StringUtils.isNotEmpty(city)) {
List<Map<String, Object>> provinceCityList = null;
if (existMap.containsKey(province + "_")) {
provinceCityList = (List<Map<String, Object>>) existMap.get(province + "_");
} else {
provinceCityList = new ArrayList<Map<String, Object>>();
existMap.put(province + "_", provinceCityList);
provinceMap.put("level", provinceCityList);
}
Map<String, Object> provinceCityMap = null;
if (existMap.containsKey(province + "_" + city)) {
provinceCityMap = (Map<String, Object>) existMap.get(province + "_" + city);
} else {
provinceCityMap = new HashMap<String, Object>();
existMap.put(province + "_" + city, provinceCityMap);
provinceCityList.add(provinceCityMap);
String citySort = String.valueOf(existMap.get(province + "_sort"));
existMap.put(province + "_sort", "null".equals(citySort) ? 1 : NumberUtils.toInt(citySort) + 1);
provinceCityMap.put("sort", existMap.get(province + "_sort"));
}
provinceCityMap.put("Name", city);
provinceCityMap.put("Code", map.get("cityCode"));
List<Map<String, Object>> provinceCityCountryList = null;
if (existMap.containsKey(province + "_" + city + "_")) {
provinceCityCountryList = (List<Map<String, Object>>) existMap.get(province + "_" + city + "_");
} else {
provinceCityCountryList = new ArrayList<Map<String, Object>>();
existMap.put(province + "_" + city + "_", provinceCityCountryList);
provinceCityMap.put("level", provinceCityCountryList);
}
String country = map.get("country");
Map<String, Object> provinceCityCountryMap = null;
if (StringUtils.isNotEmpty(country)) {
provinceCityCountryMap = new HashMap<String, Object>();
provinceCityCountryList.add(provinceCityCountryMap);
String countrySort = String.valueOf(existMap.get(province + "_" + city + "_sort"));
existMap.put(province + "_" + city + "_sort", "null".equals(countrySort) ? 1 : NumberUtils.toInt(countrySort) + 1);
provinceCityCountryMap.put("sort", existMap.get(province + "_" + city + "_sort"));
provinceCityCountryMap.put("Code", map.get("countryCode"));
provinceCityCountryMap.put("Name", country);
} else {
provinceCityCountryMap = new HashMap<String, Object>();
provinceCityCountryList.add(provinceCityCountryMap);
provinceCityCountryMap.put("sort", 1);
provinceCityCountryMap.put("Code", "");
provinceCityCountryMap.put("Name", "");
}
}
}
try {
return JsonUtils.toJson(zoneList);
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
5.4
