递归方法读取任意深度的 JSON 对象的键值

有以下json字符串

{"name":"John","age":30,"address":{"city":"New York","state":"NY","zip":"10001","coordinates":{"latitude":40.712776,"longitude":-74.005974,"accuracy":5,"details":{"description":"Exact location of the building"}},"details":{"street":"123 Main St","apt":"4B","building":{"name":"Central Park Tower","floors":98,"amenities":{"gym":true,"pool":true,"parking":{"garage":true,"valet":true}}}}}
}

读取valet层级中的值

1、maven中导入依赖,导入了两种json字符串转JsonObject的依赖

<dependencies><dependency><groupId>org.json</groupId><artifactId>json</artifactId><version>20210307</version></dependency><!-- https://mvnrepository.com/artifact/com.alibaba/fastjson --><dependency><groupId>com.alibaba</groupId><artifactId>fastjson</artifactId><version>2.0.15</version></dependency></dependencies>

2、实现递归读取json中某一层级的key值

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONObject;
//import org.json.JSONObject;public class ReadJson {public static void main(String[] args) {String jsonString = "{\"name\":\"John\",\"age\":30,\"address\":{\"city\":\"New York\",\"state\":\"NY\",\"zip\":\"10001\",\"coordinates\":{\"latitude\":40.712776,\"longitude\":-74.005974,\"accuracy\":5,\"details\":{\"description\":\"Exact location of the building\"}},\"details\":{\"street\":\"123 Main St\",\"apt\":\"4B\",\"building\":{\"name\":\"Central Park Tower\",\"floors\":98,\"amenities\":{\"gym\":true,\"pool\":true,\"parking\":{\"garage\":true,\"valet\":true}}}}}}";//JSONObject json = new JSONObject(jsonString);JSONObject json = JSON.parseObject(jsonString);//valet在第五层级String valetParking = getValueByKey(json, "valet");System.out.println(valetParking);}public static String getValueByKey(JSONObject json, String key) {String result = null;for (String k : json.keySet()) {Object value = json.get(k);if (value instanceof JSONObject) { //遇到jsonobject继续递归result = getValueByKey((JSONObject) value, key);if (result != null) {break;}} else if (k.equals(key)) { //遇到某一层级的叶子节点如果和key相等于，找到答案跳出循环返回一个result，然后再回到递归getValueByKey返回一个结果，判断不为空跳出本次递归的循环，return返回结果，再回到之前的递归返回的结果还是之前的直接不为空跳出本次递归的循环，返回return,接着再回到之前的递归....result = value.toString();break;}}return result;}}

运行过程：遇到jsonobject继续递归;遇到某一层级的叶子节点如果和key相等于，找到答案跳出循环执行return result，然后再回到递归getValueByKey返回刚才的return结果，判断不为空跳出本次递归的循环，return返回结果，再回到之前的递归返回的结果还是之前的直接不为空跳出本次递归的循环，返回return结果,接着再回到之前的递归....最终走完递归

缺点：如果寻找的key在多个层级存在，只能返回最近一个层级的key

优点：只需要传我想要的key即可

针对多个层级存在相同key的问题，可以使用下面的代码来实现

import org.json.*;public class ReadJsonV2 {public static void main(String[] args) {// 要解析的JSON字符串String jsonString = "{\"name\":\"John\",\"age\":30,\"address\":{\"city\":\"New York\",\"state\":\"NY\",\"zip\":\"10001\",\"coordinates\":{\"latitude\":40.712776,\"longitude\":-74.005974,\"accuracy\":5,\"details\":{\"description\":\"Exact location of the building\"}},\"details\":{\"street\":\"123 Main St\",\"apt\":\"4B\",\"building\":{\"latitude\":\"Central Park Tower\",\"floors\":98,\"amenities\":{\"gym\":true,\"pool\":true,\"parking\":{\"garage\":true,\"valet\":true}}}}}}";// 解析JSON字符串JSONObject jsonObject = new JSONObject(jsonString);// 获取某个层级的键//String keyString = "address.coordinates.latitude";String keyString = "address.details.building.latitude";String[] keys = keyString.split("\\.");String make = getJsonValue(jsonObject, keys);System.out.println(make); // 输出 "Ford"}private static String getJsonValue(JSONObject jsonObject, String[] keys) {JSONObject currentObject = jsonObject;for (String key : keys) {if (currentObject.has(key)) {Object obj = currentObject.get(key);if (obj instanceof JSONObject) {currentObject = (JSONObject) obj;} else {return obj.toString();}} else {return null;}}return null;}
}

在这个实现中，我们将传入的键名字符串"address.details.building.latitude"拆分成一个字符串数组{"address", "details","building","latitude"}。然后，我们将该数组传递给getJsonValue方法，该方法使用该数组来遍历JSON对象。如果存在该键名，则将其转换为JSON对象类型并将其赋值给currentObject。如果该键名不存在，返回null。如果该键对应的对象不是JSON对象类型，则将其转换为字符串并返回。

通过这种方式，我们可以轻松地使用点号分隔的字符串来查找JSON对象中的任何层级的键值对。