Class java.util.Map has generic type parameters, please use GenericTypeIndicator instead

The error points out correctly where you are going wrong

 Map<String, String> map = dataSnapshot.getValue(Map.class);

Map class uses parameter to define the types of Key and Object where as you don't give them and simply use Map.class which fails.

Try the below code - since Key are always string and we can have any type of Object for them

    Map<String, Object> map = (Map<String, Object>) dataSnapshot.getValue();

To introduce the GenericTypeIndicator, you can change this line:

Map<String, String> map = dataSnapshot.getValue(Map.class);

in to this:

GenericTypeIndicator<Map<String, String>> genericTypeIndicator = new GenericTypeIndicator<Map<String, String>>() {};
Map<String, String> map = dataSnapshot.getValue(genericTypeIndicator );

This should work well in your case. Please give it a try and let me know.

I had the same problem and solved it by handling the Object instead trying to have Firebase cast it.

Map <String, String> map = (Map)dataSnapshot.getValue();

did it for me.