API Error Handling in the Open Event Organizer Android App

Open Event Organizer is an Android App for Organizers and Entry Managers. Open Event API server acts as a backend for this App. So basically the App makes data requests to the API and in return, the API performs required actions on the data and sends back the response to the App which is used to display relevant info to the user and to update the App’s local database. The error responses returned by the API need to parse and show the understandable error message to the user.

The App uses Retrofit+OkHttp for making network requests to the API. Hence the request method returns a Throwable in the case of an error in the action. The Throwable contains a string message which can be get using the method named getMessage. But the message is not understandable by the normal user. Open Event Organizer App uses ErrorUtils class for this work. The class has a method which takes a Throwable as a parameter and returns a good error message which is easier to understand to the user.

Relevant code:

public final class ErrorUtils {

   public static final int BAD_REQUEST = 400;
   public static final int UNAUTHORIZED = 401;
   public static final int FORBIDDEN = 403;
   public static final int NOT_FOUND = 404;
   public static final int METHOD_NOT_ALLOWED = 405;
   public static final int REQUEST_TIMEOUT = 408;

   private ErrorUtils() {
       // Never Called

   public static String getMessage(Throwable throwable) {
       if (throwable instanceof HttpException) {
           switch (((HttpException) throwable).code()) {
               case BAD_REQUEST:
                   return "Something went wrong! Please check any empty field if a form.";
               case UNAUTHORIZED:
                   return "Invalid Credentials! Please check your credentials.";
               case FORBIDDEN:
                   return "Sorry, you are not authorized to make this request.";
               case NOT_FOUND:
                   return "Sorry, we couldn't find what you were looking for.";
               case METHOD_NOT_ALLOWED:
                   return "Sorry, this request is not allowed.";
               case REQUEST_TIMEOUT:
                   return "Sorry, request timeout. Please retry after some time.";
                   return throwable.getMessage();
       return throwable.getMessage();


All the error codes are stored as static final fields. It is always a good practice to follow a making the constructor private for a utility class to make sure the class is never initialized anywhere in the app. The method getMessage takes a Throwable and checks if it is an instance of the HttpException to get an HTTP error code. Actually, there are two exceptions – HttpException and IOException. The prior one is returned from the server. In the method by using the error codes, relevant good error messages are returned which are shown to the user in a snackbar layout.

It is always a good practice to show a more understandable user-friendly error messages than simply the default ones which are not clear to the normal user.

1. List of the HTTP Client Error Codes – Wikipedia Link
2. Class Throwable javadoc