Waiting until application return Sucess or Failure(AsyncCallBack) - gwt

Question

Just for example, let's check the code below
private void loadUserFromServer() {
dispatchAsync.execute(new FindLoggedUserAction(),
new AsyncCallback<FindLoggerUserResult>() {
#Override
public void onFailure(Throwable caught) {
//do something
}
#Override
public void onSuccess(BuscarUsuarioLogadoResult result) {
//dosomething with user
result.getUser();
}
operationTwo();
}
My problem is, I have to execute operationTwo(); after some result of dipatcher(Success or failure).
This is just an example, let's assume I can't put operationTwo() inside the onSucess or onFailure()
My real PROBLEM
My GateKeeper of presenters that user must be login.
private UserDTO user;
#Override
public boolean canReveal() {
if(getUser() == null){
ShowMsgEvent.fire(eventBus,"Must Login first", AlertType.ERROR);
return false;
}
return true;
}
}
public UserDTO getUser()
{
if(user == null)
{
//call server
loadUserFromServer();
}
return user;
}
private void loadUsuarioFromServer() {
dispatchAsync.execute(new BuscarUsuarioLogadoAction()
,new AsyncCallback<BuscarUsuarioLogadoResult>() {
#Override
public void onFailure(Throwable caught) {
//something
}
#Override
public void onSuccess(BuscarUsuarioLogadoResult result) {
if(!(result.getDto().equals(user)))
{
setUsuario(result.getDto(), false); //Set user UserDTO user
//event for update Presenter Login/Logout
// and Label with username
fireUserUpdateEvents();
}
else
{
setUsuario(result.getDto(), false);
}
}
});
As you can see, when a Presenter with that Gatekeeper is called and user is null,
getUser() is called, but when dispatch executes, the method doesn't wait until the return of Sucess or Failure
Result: getUser() returns null.
After the sucessful result of dispatch, getUser() returns a DTO. But, as you can see canReveal() already returned false.

Answer 1

Do not think that GateKeeper is a good approach to handle security in your case. You will not be able to reach stable work. Problem that you will have:
You are not handling network connection lost. If you code is already cached but you need to reload User it will be a big problem with double checking.
Sync calls are always problematic, specially with bad network connection. You will have tons of not responding messages.
To handle presenter access it will be better to use revealInParent method. Most of your presenter already overrides it and it looks like:
#Override
protected void revealInParent() {
RevealContentEvent.fire(...);
}
So you can just not fire Reveal event before you actually download user data. In your case the code will looks like:
#Override
protected void revealInParent() {
if(getUser() == null){
RevealContentEvent.fire(...);
return;
}
dispatchAsync.execute(new BuscarUsuarioLogadoAction()
,new AsyncCallback<BuscarUsuarioLogadoResult>() {
#Override
public void onFailure(Throwable caught) {
//something
}
#Override
public void onSuccess(BuscarUsuarioLogadoResult result) {
if(!(result.getDto().equals(user)))
{
setUsuario(result.getDto(), false); //Set user UserDTO user
//event for update Presenter Login/Logout
// and Label with username
fireUserUpdateEvents();
}
else
{
setUsuario(result.getDto(), false);
}
RevealContentEvent.fire(...);
}
});

Answer 2

We have also encountered similar problems. Its better to use Async call chaining. Since you can't do that there are two options for your problem
Setup a timer which will check from time to time whether the user is null or not and return only after when user is populated.
Use JSNI (Native code) and make the synchronous call. But beware this is bad practice

Answer 3

Yes, as Abhijith mentioned in previous answer there are 2 options -
1) Synchronous calls - which GWT doesn't support. So it is ruled out.
2) Setting timer - unless user logs in control will not come out of the timer loop. So failed status will never return from the timer. This approach serves only half of your requierment(serving only success state).
To solve your problem you try the following code snippet -
private UserDTO user;
private CanRevealCallBack revealCallBack;
public interface CanRevealCallBack {
returnStatus(boolean status);
}
#Override
public void canReveal(CanRevealCallBack callBack) {
revealCallBack = callBack;
if(user == null){
loadUserFromServer();
}
else{
revealCallBack.returnStatus( true );
}
}
private void loadUsuarioFromServer() {
dispatchAsync.execute(new BuscarUsuarioLogadoAction()
,new AsyncCallback<BuscarUsuarioLogadoResult>() {
#Override
public void onFailure(Throwable caught) {
//something
}
#Override
public void onSuccess(BuscarUsuarioLogadoResult result) {
if(!(result.getDto().equals(user)))
{
setUsuario(result.getDto(), false); //Set user UserDTO user
//event for update Presenter Login/Logout
// and Label with username
fireUserUpdateEvents();
}
else
{
setUsuario(result.getDto(), false);
}
if(result.getDto() == null){
revealCallBack.returnStatus( true );
}
else{
revealCallBack.returnStatus( false );
}
}
});
So, you have to pass a revealCallback to the canReveal method. CallBack gets executed and returns u the status on success of the async call. In returnStatus method of the callback you can program the logic with the correct user log-in status.