Perhaps the silly question will be asked now, because I am a newcomer in Java programming and in the development of Android as a whole, so I want to apologize in advance.
I need to get data from the API using Retrofit 2.0. I watched all sorts of trailings on the Internet, moreover, I even got the list of GitHub repositories. But I do not understand how to receive is not a list, but something one, concrete. For example, at the moment I need to send an e-mail and password settings method / Login to get the authorization token. But, as already mentioned above, I can’t figure out how 🙁
If someone could somehow help me somehow, I would be very grateful. I do not ask for me the code for me, please help figure it out in everything.

Answer 1, Authority 100%

Successful query results from Postman Copy and insert in http://www.jsonschema2pojo.org/, the received files, if necessary, adjust and insert the Android Studio to the project to the directory (Package) with the name model – the name is optional, just just traditionally settled. After that, you write two modules: factory and service, and put them in the project in the Network directory.

factory code:

// Import the necessary classes
Import retrofit2.retrofit;
Import retrofit2.converter.gson.gsonconverterfactory;
// We declare the factory - only static fields and methods
Public Class Apifactory {
  Private Static Final String Root_URL = "https: // your_api_address";
  Static Retrofit BuildRetrofit () {
    Return New Retrofit.Builder ()
        .BaseURL (root_url)
        .addconverterfactory (gsonconverterfactory.create ())
        .build ();
  }
  Public Static Apiservice GetService () {
    RETURN BUILDRETROFIT (). CREATE (Apiservice.class);
  }
}

Service code (taking into account the POST request and input parameters Login and password):

// import the model you got in json-pojo
// In this case, you must call your ACCESSTOKEN model
Import com.your_brand.your_app_name.model.accesstoken;
Import retrofit2.call;
Import retrofit2.http.post;
Import retrofit2.http.query;
Import retrofit2.http.headers;
Public Interface Apiservice {
  @Headers ("Content-Type: Application / JSON")
  @Post ("Auth / Login") // The path of your service to authorization
    Call & Lt; Accesstoken & GT; GetToken (
    @Query ("Login") String Login,
    @Query ("Password") STRING PASSWORD);
}

In the main part of your application to receive a token in response to a login and password, you are prescribed approximately this (taking into account how variables are named, classes, etc.):

Private void GetToken () {
  Call & Lt; Accesstoken & GT; Call = Apifactory.GetService (). GetToken (email, password);
  call.enqueue (New Callback & Lt; Accesstoken & GT; () {
    @Override
    Public Void Onresponse (Call & Lt; Accesstoken & GT; Call, Response & LT; Accesstoken & GT; Response) {
      If (response.issuccessful ()) {
        // here you just keep the token for further use
        MainActivity.Token = Response.Body (). GetData (). GetToken ();
        MainActivity.Tokenacquired = True;
        Log.d ("MyLogs", Token);
        GetTasks ();
      } else {
        MainActivity.Token = "";
        MainActivity.Tokenacquired = false;
        Log.d ("MyLogs", errorutils.errormessage (Response));
      }
    }
    @Override
    Public Void Onfailure (Call & Lt; Accesstoken & GT; Call, Throwable T) {}
  });
}

Errorutils class (optional, only for error boarding):

package com.your_brand.your_app_name.network;
Import java.io.ioException;
Import java.lang.annotation.annotation;
Import java.util.locale;
Import okhttp3.responsebody;
Import retrofit2.converter;
Import retrofit2.response;
Public Class Errorutils { 
Private Static Final String Error_Message = "HTTP code:% d \ N error:% s \ Nc error:% d";
  Private Static Apierror Parseerror (Response & LT;? & GT; Response) {
    Converter & LT; Responsebody, Apierror & GT; converter =.
        Apifactory.buildretrofit ()
            .responsebodyconverter (apierror.class, new annotation [0]);
    Apierror Error;
    Try {
      error = converter.converty (response.errorbody ());
    } Catch (IoException E) {
      Return New Apierror ();
    }
    RETURN ERROR;
  }
  Public Static String ErrorMessage (Response & Lt;? & GT; Response) {
    Try {
      APIERROR ERROR = PARSEERROR (RESPONSE);
      Return String.Format (Locale.getDefault (), Error_Message, Response.code (), Error.Message (), error.status ());
    } Catch (com.google.gson.jsonsyntaxexception e) {
      Return String.Format (Locale.getDefault (), Error_Message, Response.code (), "NULL", 0);
    }
  }
}

APIERROR class

package com.your_brand.your_app_name.network;
Import com.google.gson.annotations.serializedName;
Public Class Apierror {
  @SerializedName ("httpstatus")
  Private Int Statuscode;
  @SerializedName ("ErrorMessage")
  Private String Message;
  Public Apierror () {
  }
  Public int status () {
    Return Statuscode;
  }
  Public String Message () {
    Return Message;
  }
}

Well, here’s information for reflection. com.your_brand.your_app_name is the name of your project specified in the Java module headers. While disassemble and good night. If any questions arise – ask, but I will answer tomorrow. Sorry in advance if some typos will be in the code. Successful work!