Suggest Addresses in a SuggestBox in GWT/Java - google-app-engine

Question

I want to define a SuggestBox, which behaves like the search bar in Google Maps: When you begin to type, real addresses, starting with the typed letters, appear.
I think, that I need to use the Geocoder.getLocations(String address, LocationCallback callback) method, but I have no idea how to connect this with the oracle, which is needed by the suggest box to produce its suggestions.
Can you please give me ideas how do I connect the getLocations Method with the SuggestOracle?

Answer 1

I solved this by implementing a subclass of SuggestBox, which has it's own SuggestOracle. The AddressOracle deals as a Wrapper for the Google Maps Service, for which the class Geocoderin the Google Maps API for GWT offers abstractions.
So here is my solution:
First we implement the Widget for a SuggestBox with Google Maps suggestions
public class GoogleMapsSuggestBox extends SuggestBox {
public GoogleMapsSuggestBox() {
super(new AddressOracle());
}
}
Then we implement the SuggestOracle, which wraps the Geocoder async method abstractions:
class AddressOracle extends SuggestOracle {
// this instance is needed, to call the getLocations-Service
private final Geocoder geocoder;
public AddressOracle() {
geocoder = new Geocoder();
}
#Override
public void requestSuggestions(final Request request,
final Callback callback) {
// this is the string, the user has typed so far
String addressQuery = request.getQuery();
// look up for suggestions, only if at least 2 letters have been typed
if (addressQuery.length() > 2) {
geocoder.getLocations(addressQuery, new LocationCallback() {
#Override
public void onFailure(int statusCode) {
// do nothing
}
#Override
public void onSuccess(JsArray<Placemark> places) {
// create an oracle response from the places, found by the
// getLocations-Service
Collection<Suggestion> result = new LinkedList<Suggestion>();
for (int i = 0; i < places.length(); i++) {
String address = places.get(i).getAddress();
AddressSuggestion newSuggestion = new AddressSuggestion(
address);
result.add(newSuggestion);
}
Response response = new Response(result);
callback.onSuggestionsReady(request, response);
}
});
} else {
Response response = new Response(
Collections.<Suggestion> emptyList());
callback.onSuggestionsReady(request, response);
}
}
}
And this is a special class for the oracle suggestions, which just represent a String with the delivered address.
class AddressSuggestion implements SuggestOracle.Suggestion, Serializable {
private static final long serialVersionUID = 1L;
String address;
public AddressSuggestion(String address) {
this.address = address;
}
#Override
public String getDisplayString() {
return this.address;
}
#Override
public String getReplacementString() {
return this.address;
}
}
Now you can bind the new widget into your web page by writing the following line in the onModuleLoad()-method of your EntryPoint-class:
RootPanel.get("hm-map").add(new GoogleMapsSuggestBox());