Hi Jens,
Thanks for extensive answers, there are several things for me to learn.
My application is a bit different, I am not loading data from db, rather I
have a list of db which
I want to check db connection, and the service will return a pair <db,bool>
per each database.
I want to show the user how this process is progressing and user sees which
db has been already tested, that
is why I want to call service per db.
With this explanation, how do I solve my problem?
Best,
Al
On Saturday, May 2, 2015 at 1:46:32 PM UTC+2, Jens wrote:
>
> Ok here are some points to make your code better:
>
> 1.) First something to understand: Whenever you must provide a callback
> you can be sure that the method requiring the callback is executed
> asynchronous. In fact literally all web APIs that need to wait for
> something are asynchronous because the browser itself only has a single
> thread to execute JavaScript and that thread should never block. If it
> would block then the browser tab would be unusable for the user. So
> JavaScript uses asynchronous APIs and processes work using an event
> dispatch thread.
>
> 2.) You should never really do server requests in a loop unless you really
> know what you do. Server requests are slow and costly (think of mobile) and
> it is always better to fetch the whole list of data in a single request. So
> given your example you would do configurationService.testStrs(allStrings,
> callback) . Also keep in mind because of 1.) there is no guarantee of
> ordering. That means if your for loop does execute your testStr() method
> for "A", "B", "C" in order then the server might get these requests in
> order "B", "A", "C" and the browser get the server results in order "C",
> "A", "B".
>
> 3.) If you do 2.) and request all strings at once you only have a single
> result and thus you could move your finalizeDialogBox() into the
> onSuccess() method of your callback. So it would look like
>
> initDialogBox();
> // optional: show some loading indicator
> configurationService.testStrings(allStrings, new AsyncCallback<ArrayList<
> Boolean>>() {
>
> public void onSuccess(ArrayList<Boolean> allResults) {
> updateDialogBox(db, allResults);
> finalizeDialogBox();
> // optional: hide loading indicator
> }
>
> ....
> }
>
>
> Also note that I have used ArrayList instead of List. The reason is that
> you are using GWT-RPC which generates serializer classes for everything
> that might be transferred between client and server. If I would use List
> then GWT-RPC will generate serializers for all implementations of List even
> though your app might only use ArrayList. That makes the app larger than it
> should. Luckily the List interface does not have that much implementations
> and overhead isn't that much but it is still something to be aware of,
> especially if you use lots of libraries that might have additional List
> implementations.
>
> GWT-RPC generates a file of the form <hash>.gwt.rpc in your output folder
> which contains all classes that GWT-RPC has detected and generated
> serializers for. It is handy to look into that file from time to time to
> check if lots of unwanted things are detected. Also the GWT compile report
> gives you insight about the final JavaScript size of serializers.
>
> 4.) From a user perspective you should make sure to have some loading
> indicator while the table data loads in case the network is slow.
>
>
> -- J.
>
>
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