如何将嵌套的JSON写入HashMap<String，String>？

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

public class JsonToHashMapExample {
    public static void main(String[] args) {
        String json = "{\"key1\":\"value1\",\"key2\":{\"nestedKey\":\"nestedValue\"}}";

        try {
            ObjectMapper objectMapper = new ObjectMapper();
            JsonNode rootNode = objectMapper.readTree(json);

            HashMap<String, String> hashMap = new HashMap<>();
            parseJsonNode(rootNode, hashMap);

            // 打印解析后的HashMap
            for (Map.Entry<String, String> entry : hashMap.entrySet()) {
                System.out.println(entry.getKey() + " : " + entry.getValue());
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private static void parseJsonNode(JsonNode jsonNode, HashMap<String, String> hashMap) {
        Iterator<Map.Entry<String, JsonNode>> fields = jsonNode.fields();
        while (fields.hasNext()) {
            Map.Entry<String, JsonNode> entry = fields.next();
            String key = entry.getKey();
            JsonNode value = entry.getValue();

            if (value.isObject()) {
                HashMap<String, String> nestedHashMap = new HashMap<>();
                parseJsonNode(value, nestedHashMap);
                hashMap.put(key, nestedHashMap.toString());
            } else {
                hashMap.put(key, value.asText());
            }
        }
    }
}

key1 : value1
key2 : {nestedKey=nestedValue}