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Parsing API results on Android with Retrofit and Jackson or Gson

I am trying to parse the results of an API call which returns a unique first property.
{
"AlwaysDifferent12345": {
"fixedname1" : "ABC1",
"fixedname2" : "ABC2"
}
}
I am using retrofit2 and jackson/gson and cannot figure out how to cope with dynamic property names within the retrofit2 framework. The following works fine
data class AlwaysDifferentDTO(
#JsonProperty("AlwaysDifferent12345") val alwaysDifferentEntry: AlwaysDifferentEntry
)
I have tried
data class AlwaysDifferentDTO(
#JsonProperty
val response: Map<String, AlwaysDifferentEntry>
)
But this returns errors Can not instantiate value of type... The return value from the API is fixed i.e. map<string, object>.
I have read you can write a deserializer but it looks like I need to deserialize the whole object when all I want to do is just ignore the string associated with the response.
I have read
https://discuss.kotlinlang.org/t/set-dynamic-serializedname-annotation-for-gson-data-class/14758
and several other answers. Given unique properties names are quite common it would be nice to understand how people deal with this when using retrofit2
Thanks

Because the JSON doesn't have a 1-to-1 mapping Jackson can't map it automatically using annotations. You are going to need to make your own Deserializer.
In this tutorial you can learn how to create your own custom Deserializer for Jackson. https://www.baeldung.com/jackson-deserialization
In the tutorial you will see the first line under the deserialize function is
JsonNode node = jp.getCodec().readTree(jp);
using this line you can get the JSON node as a whole and once you have it you can call this function
JsonNode AlwaysDifferent12345Node = node.findParent("fixedname1");
Now that you have that node you can retrieve its value like shown in the rest of the tutorial. Once you have all the values you can return a new instance of the AlwaysDifferentDTO data class.

How to call dotnet api from Retrofit?

This day is the first time for me to use dotNet web API for my project.
This is the code of my controller
public IEnumerable<Waybill> Get(string id_wb) {
List<Waybill> lstWaybill = new List<Waybill>();
lstWaybill = objway.GetWaybill(id_wb).ToList();
return lstWaybill;
}
That API can work well if I'm call using this link :
http://localhost:56127/api/waybill/?id_wb=00000093
but I don't know how to call that link from my android app (I'm using retrofit)
#GET("Waybill/{id_wb}/id_wb")
Call<Waybill> getWaybillData(#Path("id_wb") String id_wb);

There are 3 options.
First one is to use Retrofit's #Query annotation.
#GET("Waybill/")
Call<Waybill> getWaybillData(#Query("id_wb") String id_wb);
The second one is to #Path annotation
#GET("Waybill/?id_wb={id_wb}") // notice the difference in your code and my code
Call<Waybill> getWaybillData(#Path("id_wb") String id_wb);
The third option is to use #Url annotation. With this option, you need to prepare fully qualified URL before calling/using getWaybillData() method in your activity or fragment. Keep in mind that #Url method overrides base URL set in Retrofit client.
#GET // notice the difference in your code and my code
Call<Waybill> getWaybillData(#Url String completeUrl);
If you follow 3rd option you need to prepare full URL in your activity like below.
String url = "http://<server_ip_address>:56127/api/waybill/?id_wb=00000093";
YourInterface api = ...
Call<Waybill> call = api.getWaybillData(url);
call.enqueue({/* implementation */});
I see a difference in the sample URL you mentioned and usage in Retrofit API interface.
In sample URL waybill is small and in API interface it is Waybill. Please ensure that you're using the right URL.

How to pass dynamic header authorization in Retrofit 2.0?

I want to pass dynamic header in retrofit using jwt,i received token using GET api and token has been saved using shared preference, i need to pass token as a header to receive user details when i login.Before that i have used volley library, in Retrofit just confusing please help me!

Put #Header on a method parameter and pass it as a value when invoking.
According to the docs:
// Replaces the header with the the value of its target.
#GET("/")
void foo(#Header("Authorization") String token, Callback<Response> cb);
Header parameters may be null which will omit them from the request. Passing a List or array will result in a header for each non-null item.
Note that HTTP headers do not overwrite each other. All headers with the same name will go in with the request. Then, it will be up to the server how they are interpreted. I recommend that you don't add multiple headers of the same name.

what is the difference between #Query and #path in Retrofit?

I wanted to use retrofit library for parsing and posting the data by passing some parameters. But When defining model class some times we will use #Serialized in-front of variable, What is the use of that Serialized.And What is the difference between #Get and #Query in passing params to API.Can Any one explain the difference.

Lets say you have api method #GET("/api/item/{id}/subitem/") so by using #Path("id") you can specify id for item in path. However your api may take additional parameters in query like sort, lastupdatetime, limit etc so you add those at end of url by #Query(value = "sort") String sortQuery
So full method will look like:
#GET("/api/item/{id}/subitem")
SubItem getSubItem(#Path("id") int itemId, #Query("sort") String sortQuery, #Query("limit") int itemsLimit);
and calling api.getSubItem(5, "name", 10) will produce url #GET("/api/item/5/subitem/?sort=name&limit=10")
and #Get is HTTP method
http://www.w3schools.com/tags/ref_httpmethods.asp says
Two commonly used methods for a request-response between a client and
server are: GET and POST.
GET - Requests data from a specified resource POST - Submits data to
be processed to a specified resource

#GET is request method. You mark method with that.
#Query is query parameter (i.e. the one in the URL). You mark method parameters with that.
#Serialized probably does not belong to Retrofit, look at its package name (move cursor there and press `Ctrl+Q in Android studio)

Why is Retrofit adding a trailing slash to all URLs?

Editing question with more details :
I understand the use of service interfaces in Retrofit. I want to make a call to a URL like this :
http://a.com/b/c (and later append query parameters using a service interface).
My limitations are :
I cannot use /b/c as a part of service interface (as path parameter). I need it as a part of base url. I have detailed the reason below.
I cannot afford to have a resultant call being made to http://a.com/b/c/?key=val. What I need is http://a.com/b/c?key=val (the trailing slash after "c" is creating problems for my API). More details below.
My Server API changes pretty frequently, and I am facing trouble on the client side using Retrofit. The main problem is that we cannot have dynamic values (non final) passed to #GET or #POST annotations for Path Parameters (like it is possible for query parameters). For example, even the number of path parameters change when the API changes. We cannot afford to have different interfaces everytime the API changes.
One workaround to this is by forming the complete URLs, that is, an Endpoint with Base_Url + Path_Parameters.
But I am wondering why is Retrofit forcibly adding a trailing slash ("/") to the base url :
String API_URL = "https://api.github.com/repos/square/retrofit/contributors";
if (API_URL.endsWith("/")) {
API_URL = API_URL.substring(0, API_URL.length() - 1);
}
System.out.println(API_URL); //prints without trailing "/"
RestAdapter restAdapter = new RestAdapter.Builder()
.setEndpoint(API_URL)
.build();
API_URL is always being reset to https://api.github.com/repos/square/retrofit/contributors/ by Retrofit internally (confirmed this by logging the request)
One workaround to this is by manually adding a "?" in the end to prevent "/" to be added: https://api.github.com/repos/square/retrofit/contributors?
Unfortunately, such request won't be accepted by our API.
Why is Retrofit forcing this behavior ?
Is there a solution for people like me who don't want a trailing slash ?
Can we have variable parameters (non final) being passed to Retrofit #GET or #POST annotations ?

You're expected to pass the base URL to the setEndpoint(...) and define /repos/... in your service interface.
A quick demo:
class Contributor {
String login;
#Override
public String toString() {
return String.format("{login='%s'}", this.login);
}
}
interface GitHubService {
#GET("/repos/{organization}/{repository}/contributors")
List<Contributor> getContributors(#Path("organization") String organization,
#Path("repository") String repository);
}
and then in your code, you do:
GitHubService service = new RestAdapter.Builder()
.setEndpoint("https://api.github.com")
.build()
.create(GitHubService.class);
List<Contributor> contributors = service.getContributors("square", "retrofit");
System.out.println(contributors);
which will print:
[{login='JakeWharton'}, {login='pforhan'}, {login='edenman'}, {login='eburke'}, {login='swankjesse'}, {login='dnkoutso'}, {login='loganj'}, {login='rcdickerson'}, {login='rjrjr'}, {login='kryali'}, {login='holmes'}, {login='adriancole'}, {login='swanson'}, {login='crazybob'}, {login='danrice-square'}, {login='Turbo87'}, {login='ransombriggs'}, {login='jjNford'}, {login='icastell'}, {login='codebutler'}, {login='koalahamlet'}, {login='austynmahoney'}, {login='mironov-nsk'}, {login='kaiwaldron'}, {login='matthewmichihara'}, {login='nbauernfeind'}, {login='hongrich'}, {login='thuss'}, {login='xian'}, {login='jacobtabak'}]
Can we have variable parameters (non final) being passed to Retrofit #GET or #POST annotations ?
No, values inside (Java) annotations must be declared final. However, you can define variable paths, as I showed in the demo.
EDIT:
Note Jake's remark in the comments:
Worth noting, the code linked in the original question deals with the case when you pass https://api.github.com/ (note the trailing slash) and it gets joined to /repos/... (note the leading slash). Retrofit forces leading slashes on the relative URL annotation parameters so it de-dupes if there's a trailing slash on the API url.