I have a JSONObject with some attributes that I want to convert into a Map<String, Object>
Is there something that I can use from the json.org or ObjectMapper?
9 Answers
You can use Gson() (com.google.gson) library if you find any difficulty using Jackson.
//changed yourJsonObject.toString() to yourJsonObject as suggested by Martin Meeser
HashMap<String, Object> yourHashMap = new Gson().fromJson(yourJsonObject, HashMap.class);use Jackson () from
HashMap<String,Object> result = new ObjectMapper().readValue(<JSON_OBJECT>, HashMap.class);This is what worked for me:
public static Map<String, Object> toMap(JSONObject jsonobj) throws JSONException { Map<String, Object> map = new HashMap<String, Object>(); Iterator<String> keys = jsonobj.keys(); while(keys.hasNext()) { String key = keys.next(); Object value = jsonobj.get(key); if (value instanceof JSONArray) { value = toList((JSONArray) value); } else if (value instanceof JSONObject) { value = toMap((JSONObject) value); } map.put(key, value); } return map; } public static List<Object> toList(JSONArray array) throws JSONException { List<Object> list = new ArrayList<Object>(); for(int i = 0; i < array.length(); i++) { Object value = array.get(i); if (value instanceof JSONArray) { value = toList((JSONArray) value); } else if (value instanceof JSONObject) { value = toMap((JSONObject) value); } list.add(value); } return list;
}Most of this is from this question: How to convert JSONObject to new Map for all its keys using iterator java
2Note to the above solution (from A Paul): The solution doesn't work, cause it doesn't reconstructs back a HashMap< String, Object > - instead it creates a HashMap< String, LinkedHashMap >.
Reason why is because during demarshalling, each Object (JSON marshalled as a LinkedHashMap) is used as-is, it takes 1-on-1 the LinkedHashMap (instead of converting the LinkedHashMap back to its proper Object).
If you had a HashMap< String, MyOwnObject > then proper demarshalling was possible - see following example:
ObjectMapper mapper = new ObjectMapper();
TypeFactory typeFactory = mapper.getTypeFactory();
MapType mapType = typeFactory.constructMapType(HashMap.class, String.class, MyOwnObject.class);
HashMap<String, MyOwnObject> map = mapper.readValue(new StringReader(hashTable.toString()), mapType);The best way to convert it to HashMap<String, Object> is this:
HashMap<String, Object> result = new ObjectMapper().readValue(jsonString, new TypeReference<Map<String, Object>>(){}));The JSONObject has a method toMap which returns Map<String,Object>.
The Maven dependency used in pom.xml:
<dependency> <groupId>org.json</groupId> <artifactId>json</artifactId> <version>20210307</version>
</dependency>Found out these problems can be addressed by using
ObjectMapper#convertValue(Object fromValue, Class<T> toValueType)As a result, the origal quuestion can be solved in a 2-step converison:
Demarshall the JSON back to an object - in which the
Map<String, Object>is demarshalled as aHashMap<String, LinkedHashMap>, by using bjectMapper#readValue().Convert inner LinkedHashMaps back to proper objects
ObjectMapper mapper = new ObjectMapper();
Class clazz = (Class) Class.forName(classType);
MyOwnObject value = mapper.convertValue(value, clazz);
To prevent the 'classType' has to be known in advance, I enforced during marshalling an extra Map was added, containing <key, classNameString> pairs. So at unmarshalling time, the classType can be extracted dynamically.
This is how I did it in Kotlin:
mutableMapOf<String, Any>().apply { jsonObj.keys().forEach { put(it, jsonObj[it]) } }import com.alibaba.fastjson.JSONObject;
Map<String, Object> map = new HashMap<String, Object>();
JSONObject rec = JSONObject.parseObject(<JSONString>);
map.put(rec.get("code").toString(), rec.get("value").toString());
