如何在onMessage事件侦听器中将项添加到ObservableList

Question

I am making two simple JMS application with JavaFx (one for sender and the other one is receiver).

But, I could not refresh the GUI of the receiver with the new arriving message from the sender.

From debugging, I noticed that the receiver received the message from the server, but the receiver could not add it to my ObservableList (which, of course, resulted in no refreshing in the GUI of the ListView).

I looked up on the internet with onMessage event, and override it (to add an item to the ObservableList there), but it is not working. After the event is raised, no element was added to the ObservableList.

This is my receiver:

public class Administrator extends Application {
    private ObservableList<String> observableList;
    private final String DESTINATION_TYPE = "queue";
    private final String RECEIVE_CHANNEL = "askDestination";
    private final String SEND_CHANNEL = "answerDestination";
    private MessageConsumer messageConsumer;
    private MessageProducer messageProducer;
    private Session session;
    private Destination destination;
    private Connection connection;

    @FXML
    public TextField tfMessage;

    @FXML
    public ListView<String> lvMessage;

    @FXML
    public Button btnSend;

    @Override
    public void start(Stage stage) throws IOException {
        Parent root = FXMLLoader.load(getClass().getResource("administratorUI.fxml"));
        stage.setTitle("Administrator");
        stage.setScene(new Scene(root, 640, 480));
        stage.setResizable(false);
        stage.show();
    }

    @Override
    public void init() throws Exception {
        super.init();
        lvMessage = new ListView<>();
        tfMessage = new TextField();
        //questionList = new ArrayList<>();
        observableList = FXCollections.observableArrayList();
        lvMessage.setItems(observableList);
        initService(RECEIVE_CHANNEL, DESTINATION_TYPE);
        getMessage(RECEIVE_CHANNEL);
        //Platform.runLater(this::updateLV);
    }

    public static void main(String[] args) {
        launch();
    }

    public void onButtonAnswerClick() {
        String message = tfMessage.getText();

        if (message.equals("")) {
            Alert alert = new Alert(Alert.AlertType.ERROR);
            alert.setContentText("Please enter your message!!");
            alert.show();
            return;
        }

        if (replyToQuestion(message, SEND_CHANNEL)) {
            tfMessage.clear();
        } else {
            handleServiceError("Service Error", "Could not send the message to the service");
        }
    }

    private void handleServiceError(String errorTitle, String errorText){
        Alert error = new Alert(Alert.AlertType.ERROR);
        error.setTitle(errorTitle);
        error.setContentText(errorText);
    }

    private void updateLV(){
        lvMessage.getItems().clear();
        lvMessage.setItems(observableList);
    }

    private void initService(String targetDestination, String destinationType){
        try {
            Properties props = new Properties();
            props.setProperty(Context.INITIAL_CONTEXT_FACTORY,
                    "org.apache.activemq.jndi.ActiveMQInitialContextFactory");
            props.setProperty(Context.PROVIDER_URL, "tcp://localhost:61616");

            // connect to the Destination called “myFirstChannel”
            // queue or topic: “queue.myFirstDestination” or “topic.myFirstDestination”
            props.put((destinationType + "." + targetDestination), targetDestination);
            Context jndiContext = new InitialContext(props);
            ConnectionFactory connectionFactory = (ConnectionFactory) jndiContext.lookup("ConnectionFactory");

            // to connect to the JMS
            connection = connectionFactory.createConnection();

            // session for creating consumers
            session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);

            // connect to the receiver destination
            //reference to a queue/topic destination
            destination = (Destination) jndiContext.lookup(targetDestination);
        } catch (NamingException | JMSException e) {
            e.printStackTrace();
        }
    }

    private boolean replyToQuestion(String message, String sendDestination) {
        try {
            initService(sendDestination, DESTINATION_TYPE);

            // for sending messages
            messageProducer = session.createProducer(destination);

            // create a text message
            Message msg = session.createTextMessage(message);

            msg.setJMSMessageID("222");
            System.out.println(msg.getJMSMessageID());

            // send the message
            messageProducer.send(msg);

            //questionList.add(message);
            updateLV();
            return true;
        } catch (JMSException e) {
            e.printStackTrace();
            return false;
        }
    }

    private void getMessage(String receiveDestination) {
        try {
            initService(receiveDestination, DESTINATION_TYPE);

            // this is needed to start receiving messages
            connection.start();

            // for receiving messages
            messageConsumer = session.createConsumer(destination);
            MessageListener listener = message -> {
                try {
                    observableList.add(((TextMessage)message).getText());
                } catch (JMSException e) {
                    e.printStackTrace();
                }
            };

            messageConsumer.setMessageListener(listener);
        } catch (JMSException e) {
            e.printStackTrace();
        }
    }
}

And my sender:

    public class User extends Application implements MessageListener {
    private static List<String> questions;
    private final String DESTINATION_TYPE = "queue";
    private final String RECEIVE_CHANNEL = "answerDestination";
    private final String SEND_CHANNEL = "askDestination";
    private String requestId;
    private MessageConsumer messageConsumer;
    private MessageProducer messageProducer;
    private Session session;
    private Destination destination;
    private Connection connection;

    @FXML
    public Button btnSend;

    @FXML
    public TextField tfMessage;

    @FXML
    public ListView lvMessage;

    @Override
    public void start(Stage stage) throws IOException {
        Parent root = FXMLLoader.load(getClass().getResource("userUI.fxml"));
        stage.setTitle("Sender");
        stage.setScene(new Scene(root, 640, 480));
        stage.setResizable(false);
        stage.show();
    }

    @Override
    public void init() throws Exception {
        super.init();
        btnSend = new Button();
        tfMessage = new TextField();
        lvMessage = new ListView();
        questions = new ArrayList<>();
        initService(RECEIVE_CHANNEL, DESTINATION_TYPE);
        getAnswer(RECEIVE_CHANNEL);
    }

    public static void main(String[] args){
        launch(args);
    }

    public void onButtonSendClick(javafx.event.ActionEvent actionEvent) {
        String message = tfMessage.getText();

        if (message.equals("")) {
            Alert alert = new Alert(Alert.AlertType.ERROR);
            alert.setContentText("Please enter your question!!");
            alert.show();
            return;
        }

        if (sendQuestion(message, SEND_CHANNEL)) {
            tfMessage.clear();
        } else {
            handleServiceError("Service Error", "Could not send the message tot the service");
        }
    }

    private void handleServiceError(String errorTitle, String errorText){
        Alert error = new Alert(Alert.AlertType.ERROR);
        error.setTitle(errorTitle);
        error.setContentText(errorText);
    }

    private void updateLV(){
        lvMessage.getItems().clear();
        lvMessage.getItems().addAll(questions);
    }

    private void initService(String targetDestination, String destinationType){
        try {
            Properties props = new Properties();
            props.setProperty(Context.INITIAL_CONTEXT_FACTORY,
                    "org.apache.activemq.jndi.ActiveMQInitialContextFactory");
            props.setProperty(Context.PROVIDER_URL, "tcp://localhost:61616");

            // connect to the Destination called “myFirstChannel”
            // queue or topic: “queue.myFirstDestination” or “topic.myFirstDestination”
            props.put((destinationType + "." + targetDestination), targetDestination);
            Context jndiContext = new InitialContext(props);
            ConnectionFactory connectionFactory = (ConnectionFactory) jndiContext.lookup("ConnectionFactory");

            // to connect to the JMS
            connection = connectionFactory.createConnection();
            // session for creating consumers
            session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);

            // connect to the receiver destination
            //reference to a queue/topic destination
            destination = (Destination) jndiContext.lookup(targetDestination);
        } catch (NamingException | JMSException e) {
            e.printStackTrace();
        }
    }

    private boolean sendQuestion(String message, String sendDestination) {
        try {
            initService(sendDestination, DESTINATION_TYPE);

            // for sending messages
            messageProducer = session.createProducer(destination);

            // create a text message
            Message msg = session.createTextMessage(message);

            msg.setJMSMessageID("111");
            System.out.println(msg.getJMSMessageID());

            // send the message
            messageProducer.send(msg);

            //questionList.add(message);
            updateLV();
            return true;
        } catch (JMSException e) {
            e.printStackTrace();
            return false;
        }
    }

    private void getAnswer(String receiveDestination) {
        try {
            initService(receiveDestination, DESTINATION_TYPE);

            // for receiving messages
            messageConsumer = session.createConsumer(destination);
            messageConsumer.setMessageListener(this);


            // this is needed to start receiving messages
            connection.start();
        } catch (JMSException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void onMessage(Message message) {
        try {
            questions.add(((TextMessage)message).getText());
            requestId = message.getJMSMessageID();
            System.out.println(requestId);
            updateLV();
        } catch (JMSException e) {
            e.printStackTrace();
        }
    }
}

The FXML of the receiver:

    <GridPane hgap="10" prefHeight="400.0" prefWidth="600.0" vgap="10" xmlns="http://javafx.com/javafx/8.0.172-ea" xmlns:fx="http://javafx.com/fxml/1" fx:controller="Administrator">
    <padding>
        <Insets bottom="10" left="10" right="10" top="10" />
    </padding>
    <Label text="Current question:" textFill="cornflowerblue" GridPane.columnIndex="0" GridPane.rowIndex="0">
        <font>
            <Font name="System Bold" size="15.0" />
        </font>
    </Label>
    <ListView fx:id="lvMessage" prefWidth="600" GridPane.columnIndex="0" GridPane.columnSpan="2" GridPane.rowIndex="1">

    </ListView>

    <HBox spacing="10" GridPane.columnIndex="0" GridPane.columnSpan="2" GridPane.rowIndex="2">
        <TextField fx:id="tfMessage" prefHeight="61.0" prefWidth="504.0" promptText="Type your answer here...">
            <font>
                <Font size="15.0" />
            </font>
        </TextField>
        <Button fx:id="btnSend" onAction="#onButtonAnswerClick" prefHeight="61.0" prefWidth="88.0" text="Send">
        </Button>
    </HBox>
   <columnConstraints>
      <ColumnConstraints />
      <ColumnConstraints />
   </columnConstraints>
   <rowConstraints>
      <RowConstraints />
      <RowConstraints />
      <RowConstraints />
   </rowConstraints>
</GridPane>

After the receiver received the message, the event is raised so I expected the ListView to be updated with the new message. However, no element was added to the ObservableList => no update in the ListView.

So, I would like to ask if what I did is wrong or correct?

Answer 1

Turn out that I was updating the ListView on the wrong thread. For those who is still interesting in the answer, I used: Platform.runLater() and registered the event listener in the start method (before stage.show() )