How to deal with the onFailrure method throwing a JsonSyntaxException?

Question

I'm having trouble understading Retrofi2 and the callback. Right now I'm receiving a JWT response from the back-end. The callback send me right in to the onFailure() Method and cuts off me of from the response body and I'm left with a JsonSyntaxException:

com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was STRING at line 1 column 1 path $

I searched on the internet for a solution, but I'm confused. Some say the Gson is expecting the JSON string with openings brace. Or something about a JSON-array not being a JSON-object. How can I check this and can I modify a presumably broken Json string?

Right now the back end tells me the response is sends-off without failure. I'm also using a HttpLoggingInterceptor which seems to give me the JWT string just fine. I'm lost and don't know what to do next.

import android.content.Context;
import android.util.Base64;
import android.widget.Toast;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonSyntaxException;
import com.ssl.app.rest.User;
import com.ssl.app.rest.UserClient;

import java.io.IOException;

import okhttp3.OkHttpClient;
import okhttp3.logging.HttpLoggingInterceptor;
import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Response;
import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;

public class LoginActivity {

    protected static void login(Context context) {
        String username = "jack";
        String password = "9375";
        String base = username + ":" +password;
        String authHeader = "Basic " + Base64.encodeToString(base.getBytes(), Base64.NO_WRAP);

        // Interceptor
        HttpLoggingInterceptor httpLoggingInterceptor = new HttpLoggingInterceptor();
        httpLoggingInterceptor.setLevel(HttpLoggingInterceptor.Level.BODY);
        OkHttpClient okHttpClient = new OkHttpClient.Builder().addInterceptor(httpLoggingInterceptor).build();

        // Setup request
        Gson gson = new GsonBuilder()
                .setLenient()
                .create();
        Retrofit.Builder builder = new Retrofit.Builder()
                .baseUrl("http://10.0.2.2:8080/")
                .addConverterFactory(GsonConverterFactory.create(gson))
                .client(okHttpClient);
        Retrofit retrofit = builder.build();
        UserClient userClient = retrofit.create(UserClient.class);

        // Request
        Call<User> loginResponseCall = userClient.getUser(authHeader);

        // Response
        loginResponseCall.enqueue(new Callback<User>() {
            @Override
            public void onResponse(Call<User> call, Response<User> response) {
                if(response.isSuccessful()){
                    Toast.makeText(context,"Login Successful :) \n"+response.body(), Toast.LENGTH_LONG).show();
                }
            }

            @Override
            public void onFailure(Call<User> call, Throwable t) {
                if (t instanceof IOException) {
                    Toast.makeText(context,"this is an actual network failure :( \n"+t, Toast.LENGTH_LONG).show();
                    System.out.println("this is an actual network failure\n" +t);

                } else if (t instanceof JsonSyntaxException) {
                    Toast.makeText(context,"Gson fails to read a malformed JSON element \n"+t, Toast.LENGTH_LONG).show();
                    System.out.println("Gson fails to read a malformed JSON element\n" +t);

                } else {
                    Toast.makeText(context,"conversion issue! big problem :( \n"+t, Toast.LENGTH_LONG).show();
                    System.out.println("conversion issue! big problem :(\n" +t);
                }
            }
        });
    }
}




    public class User {

    private String username;
    private String password;

    public User(String username, String password) {
        this.username = username;
        this.password = password;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }
}

Error

    D/OkHttp: --> POST http://10.0.2.2:8080/token
    Content-Length: 0
    Authorization: Basic am9fbjoxMbM0NQ==
    --> END POST (0-byte body)
D/OkHttp: <-- 200 http://10.0.2.2:8080/token (69ms)
    X-Content-Type-Options: nosniff
    X-XSS-Protection: 0
    Cache-Control: no-cache, no-store, max-age=0, must-revalidate
    Pragma: no-cache
    Expires: 0
    X-Frame-Options: DENY
    Content-Type: text/plain;charset=UTF-8
    Content-Length: 466
D/OkHttp: Date: Mon, 05 Dec 2022 10:23:52 GMT
    Keep-Alive: timeout=60
    Connection: keep-alive
    eyJhbGciOiJSUzI1NiJ3.eyJpc3MiOiJzZWxmIiwic3ViIjoiam9obiIsImV4cCI6MTY3MDIzOTQzNiwiaWF0IjoxNjcwMjM1ODMyLCJzY29wZSI3InJlYWQifQ.eS8Z1Q_rYsofMDTdDhMpVxxhqElCXzHUCYEjr5_t4EC_ZFO1x1Axu045Bcy8I3zhVJUVY4borFw0qBM6GuOgy_j7vOpgeTjq_JksqDHY2jd8Yif3AVHbeBb_eJV-P2iKS34kawNEI3591A7-ZqoDYveCBKqpMU1MkWL2vfWkkcat_8EroeKQCcLRyCYhkTb9Ev2_rH8Zp8wWaNs6pPkfysV0OGJX171fKGdB5pZ5hZsjwzxDMS8jLFANNGz6rIT4jiaz0apiARF86SjPFOHKM4GNrklfa2LZEr_3xyksqd0InJsilHUWr3r6ahXjoaTO3KGHWV3dcg3BidLe66YzfQ
    <-- END HTTP (466-byte body)
I/System.out: Gson fails to read a malformed JSON element
I/System.out: com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was STRING at line 1 column 1 path $




import retrofit2.Call;
import retrofit2.http.Header;
import retrofit2.http.POST;

public interface UserClient {

    @POST("token")
    Call<User> getUser(@Header("Authorization") String autHeader);
}

Answer 1

please check it your api response is array of object or object of array according to you can arrange the pojo class