Slow Converting from JsonArray to ArrayList
If there really is a performance problem with that code, please back this up with some measurements. Otherwise, read some articles concerning premature optimization and don't bother.

Nevertheless, on micro-level there are a few calls that you don't need:

Get rid of superfluous .toString() calls, e.g. replace

String Filiale = value.getString("Filiale").toString();


with

String Filiale = value.getString("Filiale"); // this already is a string


Similarly, don't parse the integers yourself after converting them to string, but instead call getInt() on the Json object:

int IdCantiere = value.getInt("IdCantiere");


Avoid the repeated call to object.length() by holding the length in a variable:

for(int i = 0, n = object.length(); i &lt; n; i++)


Still, the code should be relatively fast as-is. Naturally, there's no way to be really sure without knowing what the constructors for Cliente and Cantiere actually do. If you have a real performance problem, introduce measurements aroud the parameter extraction and the object construction.

And: measure BEFORE AND AFTER you change the code as shown above so that you actually know what effect it had. See https://stackoverflow.com/questions/504103/how-do-i-write-a-correct-micro-benchmark-in-java for some advice on how to do this.