ISO2 country code from country name

You could use the built-in Locale class:

Locale l = new Locale("", "CH");
System.out.println(l.getDisplayCountry());

prints “Switzerland” for example. Note that I have not provided a language.

So what you can do for the reverse lookup is build a map from the available countries:

public static void main(String[] args) throws InterruptedException {
    Map<String, String> countries = new HashMap<>();
    for (String iso : Locale.getISOCountries()) {
        Locale l = new Locale("", iso);
        countries.put(l.getDisplayCountry(), iso);
    }

    System.out.println(countries.get("Switzerland"));
    System.out.println(countries.get("Andorra"));
    System.out.println(countries.get("Japan"));
}