{"id":1211,"date":"2014-06-26T01:00:00","date_gmt":"2014-06-25T23:00:00","guid":{"rendered":"http:\/\/www.jensd.de\/wordpress\/?p=1211"},"modified":"2014-06-26T01:00:00","modified_gmt":"2014-06-25T23:00:00","slug":"at-your-service","status":"publish","type":"post","link":"https:\/\/www.jensd.de\/wordpress\/?p=1211","title":{"rendered":"At your Service!"},"content":{"rendered":"

The Service class (javafx.concurrency.Service) may not only be used to keep the UI reactive on long duration tasks but can also be used to change the state of controls or keep UI in a reasonable state on short term actions.<\/p>\n

Recall that a Service<\/strong><\/code> is like a reusable Task<\/strong><\/code>. A Task<\/strong><\/code> can be executed once and has to be re-instantiated to be started again. The Service<\/strong><\/code> class creates a new Task<\/strong><\/code> each time it is (re-)started (createTask()<\/code> is called then). <\/p>\n

This is the start()<\/strong><\/code>-method from javafx.concurrency.Service<\/strong><\/code> class:
\n[java]
\npublic void start() {<\/p>\n

checkThread();<\/p>\n

if (getState() != State.READY) {
\n throw new IllegalStateException(
\n “Can only start a Service in the READY state. Was in state ” + getState());
\n }<\/p>\n

\/\/ Create the task
\n task = createTask();<\/p>\n

\/\/ Wire up all the properties so they use this task
\n state.bind(task.stateProperty());
\n value.bind(task.valueProperty());
\n exception.bind(task.exceptionProperty());
\n workDone.bind(task.workDoneProperty());
\n totalWorkToBeDone.bind(task.totalWorkProperty());
\n progress.bind(task.progressProperty());
\n running.bind(task.runningProperty());
\n message.bind(task.messageProperty());
\n\ttitle.bind(task.titleProperty());<\/p>\n

\/\/ Advance the task to the “SCHEDULED” state
\n task.setState(State.SCHEDULED);<\/p>\n

\/\/ Start the task
\n executeTask(task);
\n}
\n[\/java]<\/p>\n

Note that the properties binding of the Task<\/strong><\/code> (reset()<\/code> is cleaning up all stuff).<\/p>\n

In this post want to show how I’m using Services together with a JavaFX UI, like in MQTT.fx<\/a> to connect or disconnect to a MQTT broker.<\/p>\n

A simple connection pane with 5 controls:<\/strong><\/p>\n

\"connectionPane\"<\/a><\/p>\n

Wanted appearance \/ behavior:<\/strong>
\nconnectButton<\/strong><\/code>: only enabled if: not connected AND no service is running
\ndisconnectButton<\/strong><\/code>: only enabled if: connected AND no service is running
\ncancelButton & progressIndicator<\/strong><\/code>: only visible if: any service is running
\nserviceMessageLabel<\/strong><\/code>: user feedback about the states of the services and the application<\/p>\n

\"start\"<\/a><\/p>\n

\"connecting\"<\/a><\/p>\n

\"connected\"<\/a><\/p>\n

\"disconnecting\"<\/a><\/p>\n

The controller has two properties and contains two services (inner classes):<\/strong>
\n
\nStringProperty statusMessagesProperty
\nBooleanProperty connectedProperty
\n<\/code><\/strong><\/p>\n

ConnectService<\/strong>
\n[java]
\nprivate class ConnectService extends Service {<\/p>\n

@Override
\n protected void succeeded() {
\n statusMessagesProperty().set(“Connected.”);
\n connectedProperty().set(true);
\n }<\/p>\n

@Override
\n protected void failed() {
\n statusMessagesProperty().set(“Connecting failed.”);
\n LOGGER.severe(getException().getMessage());
\n connectedProperty().set(false);
\n }<\/p>\n

@Override
\n protected void cancelled() {
\n statusMessagesProperty().set(“Connecting cancelled.”);
\n connectedProperty().set(false);
\n }<\/p>\n

@Override
\n protected Task createTask() {
\n return new Task() {
\n @Override
\n protected Void call() throws Exception {
\n updateMessage(“Connecting….”);
\n Thread.sleep(1000);
\n \/\/ DEMO: un-comment to provoke “Not on FX application thread”-Exception:
\n \/\/ connectButton.setVisible(false);
\n updateMessage(“Waiting for server feedback.”);
\n Thread.sleep(2000);
\n return null;
\n }
\n };
\n }<\/p>\n

}
\n[\/java]<\/p>\n

DisconnectService <\/strong><\/p>\n

[java]
\n private class DisconnectService extends Service {<\/p>\n

@Override
\n protected void succeeded() {
\n statusMessagesProperty().set(“”);
\n connectedProperty().set(false);
\n }<\/p>\n

@Override
\n protected void cancelled() {
\n statusMessagesProperty().set(“Disconnecting cancelled.”);
\n connectedProperty().set(false);
\n }<\/p>\n

@Override
\n protected Task createTask() {
\n return new Task() {
\n @Override
\n protected Void call() throws Exception {
\n updateMessage(“Disconnecting….”);
\n Thread.sleep(1000);
\n updateMessage(“Waiting for server feedback.”);
\n Thread.sleep(2000);
\n return null;
\n }
\n };
\n }<\/p>\n

}
\n[\/java]<\/p>\n

The wanted UI-behavior can be accomplished just by some Bindings<\/strong>
\n
\nBooleanBinding anyServiceRunning = connectService.runningProperty().or(disconnectService.runningProperty());
\nserviceRunningIndicator.visibleProperty().bind(anyServiceRunning);
\ncancelButton.visibleProperty().bind(anyServiceRunning);
\nconnectButton.disableProperty().bind(connectedProperty().or(anyServiceRunning));
\ndisconnectButton.disableProperty().bind(connectedProperty().not().or(anyServiceRunning));
\nmessagesLabel.textProperty().bind(statusMessagesProperty());
\n<\/code><\/p>\n

ChangeListeners are passing the messages from the services to the statusMessagesProperty:<\/strong>
\n
\nconnectService.messageProperty().addListener((ObservableValue observableValue, String oldValue, String newValue) -> {
\n statusMessagesProperty().set(newValue);
\n });
\ndisconnectService.messageProperty().addListener((ObservableValue observableValue, String oldValue, String newValue) -> {
\n\tstatusMessagesProperty().set(newValue);
\n});
\n<\/code><\/p>\n

Three methods to control the services:<\/strong><\/p>\n

[java]
\n @FXML
\n public void cancel() {
\n LOGGER.info(“cancel”);
\n connectService.cancel();
\n disconnectService.cancel();
\n }<\/p>\n

@FXML
\n public void connect() {
\n LOGGER.info(“connect”);
\n disconnectService.cancel();
\n connectService.restart();
\n }<\/p>\n

@FXML
\n public void disconnect() {
\n LOGGER.info(“disconnect”);
\n connectService.cancel();
\n disconnectService.restart();
\n }
\n[\/java]<\/p>\n

Nice & convenient:<\/strong>
\nInstead of verifying the state of the Service<\/strong><\/code> you can just call restart()<\/strong><\/code>.
\nrestart()<\/strong><\/code> executes:
\n1. cancel()<\/strong><\/code> (if running): cancel the executed service-task
\n2. reset()<\/strong><\/code>: clear the Service<\/strong><\/code> (task=null and unbind all stuff)
\nand then
\n3. start()<\/strong><\/code>: create new Task<\/strong><\/code> and bind its properties<\/p>\n