Accessing Web Services - JavaFX 8: A Definitive Guide to Building Desktop, Mobile, and Embedded Java Clients - page 509

JsonObject jsonObject = jr.readObject();
JsonArray jsonArray = jsonObject.getJsonArray("items");
ObservableList<Question> answer = FXCollections.observableArrayList();
jsonArray.iterator().forEachRemaining((JsonValue e) -> {
JsonObject obj = (JsonObject) e;
JsonString name = obj.getJsonObject("owner").getJsonString("display_name");
JsonString quest = obj.getJsonString("title");
JsonNumber jsonNumber = obj.getJsonNumber("creation_date");
Question q = new Question(name.getString(), quest.getString(),
jsonNumber.longValue() * 1000);
System.out.println("Adding question "+q);
answer.add(q);
});
return answer;
}
};
}
}
The QuestionRetrievalService extends Service and thus has to implement a createTask method.
When the Service is started, this task is executed in a separate Thread . The createTask method on the
QuestionRetrievalService creates a new Task and returns it. The signature of this method,
Task<ObservableList<Question>>createTask(),
ensures that the Task creates an ObservableList of questions. The generic type parameter ObservableList<Question>
is the same as the type parameter in the declaration of the Service . As a consequence, the getValue() method of the
Service will also return an ObservableList of Question s.
Indeed, the following code snippet states that the questionRetrievalService.getValue() should return an
ObservableList<Question>.
ObservableList<Question> answer = FXCollections.observableArrayList();
...
if (now == State.SUCCEEDED) {
answer.addAll(service.getValue());
}
The Task instance that we created in the QuestionRetrievalService has to implement the call method. This
method is actually doing what the getObservableList method in the previous examples was doing: retrieving the
data and parsing them.
Although the real work in a Service (the Task created by createTask ) is done in a background Thread , all
methods on the Service , including the getValue() call, should be accessed from the JavaFX Thread . The internal
implementation makes sure that all changes to the available properties in the Service are executed on the JavaFX
application Thread .
Running the example gives the exact same visual output as running the previous example. However, we added
some System.out messages for clarity. If we run the example, the following messages can be seen on the console.
State of service is READY
State of service is SCHEDULED