How to get required fields of an SObject in Apex

public class DynamicApex {
    public FieldWrapper getFields(String objName) {
        try {
            FieldWrapper wr = new FieldWrapper();
            for (Schema.SObjectField f : Schema.getGlobalDescribe().get(objName).getDescribe().fields.getMap().values()) {
                Schema.DescribeFieldResult r = f.getDescribe();
                if (!r.isNillable() && r.isCreateable() && !r.isDefaultedOnCreate()) {
                    wr.requiredFields.add(r.getName());
                } else {
                    wr.otherFields.add(r.getName());
                }
            }
            return wr;
        } catch (Exception e) {
            throw new TypeException(e.getMessage());
        }
    }

    public class FieldWrapper {
        public List<String> requiredFields;
        public List<String> otherFields;

        FieldWrapper() {
            this.requiredFields = new List<String>();
            this.otherFields = new List<String>();
        }
    }
}