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Parsing json list when there is an exceptional objects as well using Retrofit2

Previously I was receiving the response like this:
I was parsing it like: Call<List<MyObject>> getList();
But now there are some new elements were added and the response changed to:
How to parse this object now? I searched my could not find any solutions.
This is how I am setting up my client.
This is the json object which i recieve as a response:
{"map":{"01":{"F":".","E":".","D":null,"C":null,"B":".","A":"."},"02":{"F":".","E":".","D":null,"C":null,"B":"Z","A":"."},"03":{"F":"A","E":"A","D":null,"C":null,"B":"A","A":"A"},"board":false,"type":{"num":"TT334","board":"WW","date":"31MAR","route":"AWETSW","pcount":""}}}
I dont

There are two potential solutions:
You create a DTO. Gson will ignore fields you don't map in your dto. Your json doesn't use a list it is entirely objects.
You manually parse the json using Gson's JsonReader
You can use a mixture of DTOs and manual parsing. I have done this for large json datasets and inconsistent datasets.

Swift to Kotlin: Struct to Data Class Example

I have converted the following Swift code:
struct FooModel: Decodable {
public let id: String
public let bars: [[BarModel]]
}
to this Kotlin code:
data class FooModel (val id: String, val bars: List<List<BarModel>>)
The issue I am encountering, is my id is coming in null for the Kotlin code (via gson). Everything else in the Kotlin conversion is working fine and the entire JSON is populating all data classes, except for this tiny piece (the id variable).
I suspect my conversion here is the cause, any ideas?

If the id should be nullable do it like this:
data class FooModel (
val id: String?,
val bars: List<List<BarModel>>
)
The question mark makes this property nullable.

If the JSON you are getting is correct (the id value is there and coming to you as a string), your code should work. It's unclear what could be going wrong here if that's the case.
However, it is worth knowing that there is a big potential "gotcha" with Gson that you should be aware of: it's possible to declare a variable of a data class as non-nullable but still get a null after conversion. This can happen when an expected value is missing from the JSON response. In these cases Gson does not throw an error and I only found out later when I got a crash trying to access the non-nullable variable that should never have made it to me as null. I discovered this is a consequence of Gson using something like Class.newInstance() instead of a regular constructor when it creates these data classes, and then uses reflection to populate the data. More is written about this in another answer here: Why Kotlin data classes can have nulls in non-nullable fields with Gson?
Depending on your use case you might consider this to be a design flaw and a reason to avoid Gson in favor of other JSON serialization libraries. My personal favorite at the moment is Square's Moshi.

You can check if the value type you are getting from server matches with your variable id i.e. String on both the sides. Secondly you can try using SerializedName("id") included in library:
implementation 'com.google.code.gson:gson:2.9.0'

How to handle such a json properly?

The problem is next.
In response I have JSON like
{
object: {
// a lot of different fields
}
}
I use Retrofit with gson parser. What I really need is just this object. I don't want to create class for response with the only one field. All responses server send in a such manner. As far I understand somewhere I need place simple code for fetching that one object and then use default parser for it.
Probably sorry for stupid question. I used Volley and there was quite a different approach.

Instead of creating a special class to handle this (and another special class for every other server response), just use Map<String, YourRealObjectType>. Then use this method to extract the YourRealObjectType instance for each response:
public static <T> T getFirstValue(Map<String, T> map) {
return map.values().iterator().next();
}

you can convert class into JsonObject class. then cal iterate all the elements in it one by one
#Get
ObservablegetData();
Note : use JsonObject not JSONObject

When using GSON, do I have to keep the same POJO at REST-WS consumer & provider end for serialization & deserialization?

I am new to GSON, JSON & hence asking the question:
At the android end, I have to send a booking information to the REST WS on the server. So here is the question:
I have a BookingDTO & I use GSON to serialize it. I send it the REST WS on the server. Now do I also need the same BookingDTO at the server end for GSON deserialize it? (But that would mean tight coupling right?) Do I have to use GSON or can I use normal JSON?
What should be my approach?

You can use Json and parse that content into your objects or directly deal with JsonObject and JsonArray in your methods (server side).
if you want to use objects like BookingDTO you can either re create the classes on android project or reuse those classes from your server side, (or vice versa).
by creating a JAR file that only contains those classes (ex, export model package only) where all POJO classes are located.
using a JAR file makes you maintain a consistency between server and client code, when you add/delete a field, you don't have to change 2 classes, just change in one place and re export the JAR.
now to the tight coupling issue, i don't think there is a one here.
because you are using a list of classes (and you need them in 2 or more separate locations/projects...) this is not coupling, this is reusing same code which should be a good practice.
Coupling is -for example- when Class A is a member of Class B, but it's not when you use Class A and Class B in 2 different systems/components ...

do I also need the same BookingDTO at the server end for GSON
deserialize it?
Simply put, yes, you'll have to prepare a POJO in order to receive the request. So, for that to happen, JSON deserializer will try to parse the properties off JSON request and map that to a POJO of server.
With Spring, we do stuffs like the following. This is a creating a controller of POST request type expecting to habe a param of BookingDTO type. We use Jackson library for JSON serialize and deserialize.
#RequestMapping(value = {"/update"}, method = RequestMethod.POST)
#ResponseBody
public void update(#RequestBody BookingDTO bookingDTO) throws FamsException {
// Do what you intend to do with this bookingDTO object sent from client side(Android)
}
As it stands, if your JSON property name matches with the property name and type of BookingDTO then it can map those and you'll get BookingDTO bookingDTO object with all the matched properties.
Be sure not to send JSON request with property that isn't in the BookingDTO POJO. Otherwise, server will throw a 400 BAD REQUEST error.
Note that, you can also send Map as parameter. This won't require a matching POJO at server side. You can construct a different object by getting the data out of Map the way you like.
Hope you get the idea.

Is there any way to directly handle json in android/java without convert [duplicate]

I was wondering if somewhere out there exists a java library able to query a JSONObject. In more depth I'm looking for something like:
String json = "{ data: { data2 : { value : 'hello'}}}";
...
// Somehow we managed to convert json to jsonObject
...
String result = jsonObject.getAsString("data.data2.value");
System.out.println(result);
I expect to get "hello" as output.
So far, the fastest way I have found is using Gson:
jsonObject.getAsJsonObject("data").getAsJsonObject().get("data2").getAsJsonObject("value").getAsString();
It's not actually easy to write and read. Is there something faster?

I've just unexpectedly found very interesting project: JSON Path
JsonPath is to JSON what XPATH is to XML, a simple way to extract parts of a given document.
With this library you can do what you are requesting even easier, then my previous suggestion:
String hello = JsonPath.read(json, "$.data.data2.value");
System.out.println(hello); //prints hello
Hope this might be helpful either.

While not exactly the same, Jackson has Tree Model representation similar to Gson:
JsonNode root = objectMapper.readTree(jsonInput);
return root.get("data").get("data2").get("value").asText();
so you need to traverse it step by step.
EDIT (August 2015)
There actually is now (since Jackson 2.3) support for JSON Pointer expressions with Jackson. So you could alternatively use:
return root.at("/data/data2/value").asText();

First of all, I would recommend consider JSON object binding.
But in case if you get arbitrary JSON objects and you would like process them in the way you described, I would suggest combine Jackson JSON processor along with Apache's Commons Beanutils.
The idea is the following: Jackson by default process all JSON's as java.util.Map instances, meanwhile Commons Beanutils simplifies property access for objects, including arrays and Map supports.
So you may use it something like this:
//actually it is a Map instance with maps-fields within
Object jsonObj = objectMapper.readValue(json, Object.class);
Object hello = PropertyUtils.getProperty(jsonObj, "data.data2.value")
System.out.println(hello); //prints hello

You can use org.json
String json = "{ data: { data2 : { value : 'hello'}}}";
org.json.JSONObject obj = new org.json.JSONObject(json);
System.out.println(obj.query("/data/data2/value"));

I think no way.
Consider a java class
class Student {
Subject subject = new Subject();
}
class Subject {
String name;
}
Here if we want to access subject name then
Student stud = new Student();
stud.subject.name;
We cant access name directly, if so then we will not get correct subject name. Like here:
jsonObject.getAsJsonObject("data")
.getAsJsonObject()
.get("data2")
.getAsJsonObject("value")
.getAsString();
If you want to use same like java object then use
ClassName classObject = new Gson().fromJson(JsonString, ClassName.class);
ClassName must have all fields to match jsonstring. If you have a jsonobject inside a jsonobject then you have to create separate class like I'm doing in Student and Subject class.

Using Java JSON API 1.1.x (javax.json) one can make use of new JavaPointer interface. Instance implementing this interface can be considered to some extend as kind of XPath expression analog (see RFC-6901 for details). So in your case you could write this:
import javax.json.*;
//...
var jp = Json.createPointer("/data/data2/value");
System.out.println(jp.getValue(jsonObject));
In 1.1.4 version of JSON there's also nice addition to JsonStructure interface (which is implemented by JsonObject and JsonArray), namely getValue(String jsonPointer). So it all comes down to this simple one-liner:
System.out.println(jsonObject.getValue("/data/data2/value"));