How to Convert Json to a Hashmap Using Gson

How can I convert JSON to a HashMap using Gson?

Here you go:

import java.lang.reflect.Type;
import com.google.gson.reflect.TypeToken;

Type type = new TypeToken<Map<String, String>>(){}.getType();
Map<String, String> myMap = gson.fromJson("{'k1':'apple','k2':'orange'}", type);

json array in hashmap using google gson

Your JSON is an array of objects, not anything resembling a HashMap.

If you mean you're trying to convert that to a List of HashMaps ... then that's what you need to do:

Gson gson = new Gson();
Type listType = new TypeToken<List<HashMap<String, String>>>(){}.getType();
List<HashMap<String, String>> listOfCountry = 
    gson.fromJson(sb.toString(), listType);

Edit to add from comments below:

If you would like to deserialize to an array of Country POJOs (which is really the better approach), it's as simple as:

class Country {
    public String countryId;
    public String countryName;
}
...
Country[] countryArray = gson.fromJson(myJsonString, Country[].class);

That said, it's really better to use a Collection:

Type listType = new TypeToken<List<Country>>(){}.getType();
List<Country> countryList = gson.fromJson(myJsonString, listType);

How to convert JSON fields into a JAVA map using GSON

Declaring Alert object like this:

public class Alert {
    private String description;
    private String status;
    private Map<String, String> labels;
    ...
}

works for me and this code

Alert myAlert = gson.fromJson(alertJSON, Alert.class);
System.out.println(myAlert.getLabels());

prints the map as {field1=value1, field2=value2, field100=value100}

So that no intermediate object is required

JSON to hashmap with GSON

If you add a closing } to

{
"someText": {
    "text1": "lorem ipsum",
    "text2": "ipsum lorem"
}}
 ^

thus making your JSON well formed, the following

myTexts t = new Gson().fromJson(myJsonFile, myTexts.class);
System.out.println(t.someText);

prints

{text1=lorem ipsum, text2=ipsum lorem}

which seems to be what you are expecting.

Gson to HashMap

Use TypeToken, as per the GSON FAQ:

Gson gson = new Gson();
Type stringStringMap = new TypeToken<Map<String, String>>(){}.getType();
Map<String,String> map = gson.fromJson(json, stringStringMap);

No casting. No unnecessary object creation.

Convert a JSON String to a HashMap

In recursive way:

public static Map<String, Object> jsonToMap(JSONObject json) throws JSONException {
    Map<String, Object> retMap = new HashMap<String, Object>();
    
    if(json != JSONObject.NULL) {
        retMap = toMap(json);
    }
    return retMap;
}

public static Map<String, Object> toMap(JSONObject object) throws JSONException {
    Map<String, Object> map = new HashMap<String, Object>();

    Iterator<String> keysItr = object.keys();
    while(keysItr.hasNext()) {
        String key = keysItr.next();
        Object value = object.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;
}

Using Jackson library:

import com.fasterxml.jackson.databind.ObjectMapper;

Map<String, Object> mapping = new ObjectMapper().readValue(jsonStr, HashMap.class);

Parsing JSON object into a Map using Gson - JsonSyntaxException

it is easy to check:

    Map<String,Attribute> attributes = new HashMap<>();
    attributes.put("key_0", new Attribute("value_0", "name_0"));// I added constructor and getter/setter methods to class Attribute
    attributes.put("key_1", new Attribute("value_1", "name_1"));
    attributes.put("key_2", new Attribute("value_2", "name_2"));
    //serialize using ObjectMapper
    ObjectMapper mapper = new ObjectMapper();
    var s = mapper.writeValueAsString(attributes);
    System.out.println(s);

output:

{
   "key_2":{
      "value":"value_2",
      "name":"name_2"
   },
   "key_1":{
      "value":"value_1",
      "name":"name_1"
   },
   "key_0":{
      "value":"value_0",
      "name":"name_0"
   }
}

How to convert nested json into Map without typecasting using Gson

I would say you can convert the json string into Map<String, JsonElement> so that you have so methods to find nested object is JsonObject or JsonArray. So in the blow example main is key with JsonObject as value

main: {
        temp:8.1, 
        pressure:1007.0, 
        humidity=93.0, 
        temp_min=7.0, 
        temp_max=10.0
      }

You can parse the value into Map by using fromJson

Map<String, Object> resultMap = new Gson().fromJson(jsonString, new TypeToken<Map<String, Object>>() {
        }.getType());

        for (Map.Entry<String, Object> entry : resultMap.entrySet()) {
            System.out.println(entry);
        }

        System.out.println(resultMap.get("temp"));
        Map<String, Object> mainMap = new Gson().fromJson(resultMap.get("main").toString(), new TypeToken<Map<String, Object>>() {
        }.getType());
        System.out.println("Temp: " + mainMap.get("temp"));