Detect offline error in Retrofit 2

11/25 2016 on Android, Programming

Displaying ‘no internet connection’ error is quite a common requirement. The sample below demonstrates how to make Retrofit 2 throw ‘no internet connection’ exception.

Essentially, you’ll create a class that implements Interceptor so that you can perform a network connectivity check before executing the request.

ConnectivityInterceptor.java

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public class ConnectivityInterceptor implements Interceptor {
 
    private Context mContext;
 
    public ConnectivityInterceptor(Context context) {
        mContext = context;
    }
 
    @Override
    public Response intercept(Chain chain) throws IOException {
        if (!NetworkUtil.isOnline(mContext)) {
            throw new NoConnectivityException();
        }
 
        Request.Builder builder = chain.request().newBuilder();
        return chain.proceed(builder.build());
    }
 
}

If the app knows there is no connectivity, stop and throw exception there. We will need a reference to Context object in order to check connectivity.




NetworkUtil.java

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public static boolean isOnline(Context context) {
	ConnectivityManager connectivityManager = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
	NetworkInfo netInfo = connectivityManager.getActiveNetworkInfo();
	return (netInfo != null && netInfo.isConnected());
}

NoConnectivityException.java

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public class NoConnectivityException extends IOException {
 
    @Override
    public String getMessage() {
        return "No connectivity exception";
    }
 
}

Creating a custom Exception class allows us to catch it by Exception class type for error handling.

When instantiating a Retrofit service,

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OkHttpClient client = new OkHttpClient.Builder()
        .addInterceptor(new ConnectivityInterceptor(context))
        .build();
 
MyRetrofitService service = new Retrofit.Builder()
        .baseUrl("https://example.com)
        .client(client)
        .addConverterFactory(GsonConverterFactory.create())
        .build()
        .create(MyRetrofitService.class);

In try-catch block for Retrofit web service failure,

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if (exception instanceof NoConnectivityException) {
    // No internet connection
}

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