GWT RPC mechanism how to use non void return type - gwt

Question

I have a scenario wherein I need to specify a return type to the Synchrnous function, the code is as follows :
#RemoteServiceRelativePath("show_box")
public interface ShowBoxCommandService extends RemoteService{
public ArrayList<String> showBox();
}
The implementation of the method on the server is :
public ArrayList<String> showBox() {
ArrayList<String> box = new ArrayList<String>();
Iterator<Box> boxes = BoxRegistry.getInstance().getBoxes();
while (boxes.hasNext()) {
box.add(boxes.next().toString());
}
return box;
}
I am trying to define the callback variable in the following format at the client side in order to call the method
AsyncCallback<Void> callback = new AsyncCallback<Void>() {
public void onFailure(Throwable caught) {
// TODO: Do something with errors.
// console was not started properly
}
#Override
public void onSuccess(Void result) {
// TODO Auto-generated method stub
// dialog saying that the console is started succesfully
}
};
update with the aync interface code :
public interface ShowBoxCommandServiceAsync {
void showBox(AsyncCallback<ArrayList<String>> callback);
}
But this is causing the definition of the method in the Async method to change.
Any ideas or clues will be helpful.
Thanks,
Bhavya
P.S. Apologies if this is a repetition

Answer 1

The callback should be:
AsyncCallback<ArrayList<String>> callback = new AsyncCallback<ArrayList<String>>() {
public void onFailure(Throwable caught) {
// TODO: Do something with errors.
// console was not started properly
}
#Override
public void onSuccess(ArrayList<String> result) {
// TODO Auto-generated method stub
// dialog saying that the console is started succesfully
}
};
If you don't need to utilize the result then you can ignore it, but if that is the case, you should probably question your design and why you would need the method to return an ArrayList<String> in the first place.

Answer 2

If the service interface looks like this:
public interface ShowBoxCommandService extends RemoteService {
public ArrayList<String> showBox();
}
then you must have an associated async interface:
public interface ShowBoxCommandServiceAsync {
public void showBox(AsyncCallback<ArrayList<String>> callback);
}
Which means, that the type of the callback that you should pass to showBox is AsyncCallback<ArrayList<String>>.
new AsyncCallback<ArrayList<String>>() {
#Override
public void onSuccess(ArrayList<String> list) {
// ...
}
#Override
public void onFailure(Throwable caught) {
// ...
}
}

Answer 3

Your callback should not be Void. If your synchronous method returns a List of Strings, the async callback method should receive the List. You'll have to use the ArrayList, because the class needs to implement the Serializable interface.
AsyncCallback<ArrayList<String>> callback = new AsyncCallback<ArrayList<String>>() {
public void onFailure(Throwable caught) {
// TODO: Do something with errors.
// console was not started properly
}
#Override
public void onSuccess(ArrayList<String> result) {
// TODO Auto-generated method stub
// dialog saying that the console is started succesfully
}
};

Answer 4

Huh? Your method returns an ArrayList and you are declaring void in your call?
Change <Void> to <ArrayList<String>>