改型不检索AccessToken

Question

我一直在学习本教程，因为我被告知Retrofit是用于oAuth和网络调用的最佳API： Retrofit oAuth2 tutorial

似乎运行良好，并且我已检索到授权代码，没有任何问题。但是，当使用他们提供的代码将其交换为访问令牌时，我似乎得到了nullpointer并成为Retrofit的初学者，我不确定自己做错了什么

ServiceGenerator类：

public class ServiceGenerator {

public static final String API_BASE_URL = "https://xxxx.xxxx.com/oauth/";

private static OkHttpClient.Builder httpClient = new OkHttpClient.Builder();

private static Retrofit.Builder builder =
        new Retrofit.Builder()
                .baseUrl(API_BASE_URL)
                .addConverterFactory(GsonConverterFactory.create());

private static Retrofit retrofit = builder.build();

public static <S> S createService(Class<S> serviceClass) {
    return createService(serviceClass, null);
}

public static <S> S createService(
        Class<S> serviceClass, String clientId, String clientSecret) {
    if (!TextUtils.isEmpty(clientId)
            && !TextUtils.isEmpty(clientSecret)) {
        String authToken = Credentials.basic(clientId, clientSecret);
        return createService(serviceClass, authToken);
    }

    return createService(serviceClass, null, null);
}

public static <S> S createService(
        Class<S> serviceClass, final String authToken) {
    if (!TextUtils.isEmpty(authToken)) {
        AuthenticationInterceptor interceptor =
                new AuthenticationInterceptor(authToken);

        if (!httpClient.interceptors().contains(interceptor)) {
            httpClient.addInterceptor(interceptor);

            builder.client(httpClient.build());
            retrofit = builder.build();
        }
    }
    return retrofit.create(serviceClass);
}

}

AuthenticationInterceptor类：

public class AuthenticationInterceptor implements Interceptor {

private String authToken;

public AuthenticationInterceptor(String token) {
    this.authToken = token;
}

@Override
public Response intercept(Chain chain) throws IOException {
    Request original = chain.request();

    Request.Builder builder = original.newBuilder()
            .header("Authorization", authToken);

    Request request = builder.build();
    return chain.proceed(request);
}

}

访问令牌类：

public class AccessToken {

private String accessToken;
private String tokenType;

public String getAccessToken() {
    return accessToken;
}

public String getTokenType() {
    // OAuth requires uppercase Authorization HTTP header value for token type
    if (! Character.isUpperCase(tokenType.charAt(0))) {
        tokenType =
                Character
                        .toString(tokenType.charAt(0))
                        .toUpperCase() + tokenType.substring(1);
    }

    return tokenType;
}

}

最重要的是，我的oAuth类：

public class oAuthAuthentication extends Activity {
// you should either define client id and secret as constants or in string resources
private final String clientId = "xxxxxxxxxxxxxxx";
private final String clientSecret = "xxxxxxx";
private final String redirectUri = "https://xxxx.xxxx.xxx/rest/callback.html";
private String AUTH_URL;
private String AuthCode;
String grantType;
AccessToken accessToken;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.oauth);

    Button loginButton = (Button) findViewById(R.id.login);
    loginButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            String url = AUTH_URL;
            Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse(url));
            startActivity(intent);
        }
    });
}

@Override
protected void onResume() {
    super.onResume();

    // the intent filter defined in AndroidManifest will handle the return from ACTION_VIEW intent
    Uri uri = getIntent().getData();
    if (uri != null && uri.toString().startsWith(redirectUri)) {
            new AsyncTaskRunner().execute();
        } else {
            Log.e("ERROR", "Error has occured with AuthCode");
        }
    }




public interface LoginService {
        @FormUrlEncoded
        @POST("/oauth/token")
        Call<AccessToken> getAccessToken(
                @Field("code") String code,
                @Field("grant_type") String grantType,
                @Field("client_id") String clientID,
                @Field("client_secret") String clientSecret,
                @Field("redirect_uri") String redirectUri);

    }

private class AsyncTaskRunner extends AsyncTask<String, String, String> {
    @Override
    protected String doInBackground(String... params) {
        Uri uri = getIntent().getData();
        if (uri != null && uri.toString().startsWith(redirectUri)) {
            // use the parameter your API exposes for the code (mostly it's "code")
            String code = uri.getQueryParameter("code");
            if (code != null) {
                AuthCode = code;
                LoginService loginService =
                        ServiceGenerator.createService(LoginService.class, clientId, clientSecret);
                Call<AccessToken> call = loginService.getAccessToken(code, "authorization_code");
                try {
                    accessToken = call.execute().body();
                    Log.e("token", accessToken.toString());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        return String.valueOf(accessToken);
    }
}

}

我要访问的AccessToken端点是https://xxxx.xxxx.com/oauth/token

使用Retrofit for oAuth的人可以帮助我吗？ P.s.我检查了我所有的值都是正确的，ID，机密，代码正在正常生成，并且Grant_type应该等于所述的“ authorization_code”。