The Best Way to Debug Retrofit Error Messages

Question

I'm new to Retrofit. I have used Volley, and I kind of like Retrofit. I was just about to select Retrofit when I ran into this very non-descriptive error message when trying to do a POST.

 Exception in thread "main" retrofit.RetrofitError
    at retrofit.RetrofitError.httpError(RetrofitError.java:37)
    at retrofit.RestAdapter$RestHandler.invokeRequest(RestAdapter.java:413)
    at retrofit.RestAdapter$RestHandler.invoke(RestAdapter.java:282)
    at myapi.api.$Proxy7.logon(Unknown Source)
    at myapi.api.TestDriver.main(TestDriver.java:94)

Well, I must say that this type of error message is about as useful as a warm jacket in the Sahara.

Does anyone even know where to begin with debugging this type of message? I really am not about to delegate to a REST api that does not provide useful error messages.

Answer 1

Create a custom ErrorHandler for Retrofit.

I found that catching the error didn't provide a whole lot of extra information but creating a custom ErrorHandler for Retrofit allowed me to dig deeper into the actual error, like so:

class MyErrorHandler implements ErrorHandler {
  @Override public Throwable handleError(RetrofitError cause) {
    Response r = cause.getResponse();
    if (r != null && r.getStatus() == 401) {
      return new UnauthorizedException(cause);
    }
    return cause;
  }
}

RestAdapter restAdapter = new RestAdapter.Builder()
    .setEndpoint("https://api.github.com")
    .setErrorHandler(new MyErrorHandler())
    .setLogLevel(RestAdapter.LogLevel.FULL)  // Do this for development too.
    .build();

From the Custom Synchronous Error Handling section on Retrofit Page.

Set the Log Level to FULL as well, as shown in above config code.

Answer 2

You probably want to add a catch clause to TestDriver.main:

try {
  service.logon();
} catch (RetrofitError e) {
  System.out.println(e.getResponse().getStatus());
}

Answer 3

Unfortunately RetrofitError (1.6.1) was tricky. 401's made getResponse() always return null which made it hard to tell if its a connection issue or authentication issue. At least for me, I had to look at the message to get the 401 error. Hopefully this helps someone else trying to do something similar.

public class RetrofitErrorHandler implements ErrorHandler {

    @Override
    public Throwable handleError(RetrofitError cause) {

        if (cause.isNetworkError()) {
            if(cause.getMessage().contains("authentication")){
                //401 errors
                return  new Exception("Invalid credentials. Please verify login info.");
            }else if (cause.getCause() instanceof SocketTimeoutException) {
                //Socket Timeout
                return new SocketTimeoutException("Connection Timeout. " +
                        "Please verify your internet connection.");
            } else {
                //No Connection
                return new ConnectException("No Connection. " +
                        "Please verify your internet connection.");
            }
        } else {

            return cause;
        }
    }

}