How to read from USB and display

[Enrico Morelli]

Dear,

I'm trying to create a graphical program to read barcodes from a USB device. I have the following code:

public class Main extends Application {

    private TextArea logTextArea;
    @Override
    public void start(Stage primaryStage) {
        primaryStage.setTitle("JavaFX Application");

        // Main Page
        BorderPane mainLayout = new BorderPane();
        HBox buttonBox = new HBox(10);
        buttonBox.setAlignment(Pos.CENTER);
        Button caricaButton = new Button("Carica");
        Button scaricaButton = new Button("Scarica");
        Label label = new Label("");


        buttonBox.getChildren().addAll(caricaButton, scaricaButton);
        mainLayout.setTop(buttonBox);
        mainLayout.setBottom(label);

        caricaButton.setOnAction(event -> {      
                String input = LoadBarCode.display();
                label.setTextFill(Color.web("green"));
                label.setText(input);
           
        });

      
        // Create the scene
        Scene mainScene = new Scene(mainLayout, 400, 300);
        primaryStage.setScene(mainScene);
        primaryStage.show();
    }

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

public class LoadBarCode {
    public static String display() {

        HashMap<String, Integer> barCodes = new HashMap<>();
        String portaSeriale = "/dev/ttyACM0";
        Stage stage = new Stage();
        stage.initModality(Modality.APPLICATION_MODAL);
        TableView tableView = new TableView();
        TableColumn<ReadData, String> column1 = new TableColumn<>("Product Code");
        column1.setCellValueFactory(new PropertyValueFactory<>("barCode"));

        TableColumn<ReadData, String> column2 = new TableColumn<>("Product #");
        column2.setCellValueFactory(new PropertyValueFactory<>("products"));

        tableView.getColumns().add(column1);
        tableView.getColumns().add(column2);


            Button button = new Button("Submit");
            button.setOnAction(e -> {
                stage.close();
            });


            BorderPane resultLayout = new BorderPane();
            VBox box = new VBox(10);
            box.getChildren().addAll(tableView, button);
            resultLayout.setCenter(box);

            Scene resultScene = new Scene(resultLayout, 400, 300);
            stage.setScene(resultScene);

        stage.showAndWait();
        while (true) {
            try {
                FileInputStream fileInputStream = new FileInputStream(portaSeriale);

                // Crea un buffer per leggere i dati
                byte[] buffer = new byte[1024];
                int bytesRead;

                while (true) {
                    synchronized (fileInputStream) {
                        bytesRead = fileInputStream.read(buffer);
                    }

                    if (bytesRead == -1) {
                        // Se il dispositivo viene disconnesso, esce dal ciclo interno
                        break;
                    }

                    String dati = new String(buffer, 0, bytesRead).strip();
                    tableView.getItems().add(new ReadData(dati, 1));

                    System.out.println(dati);
                    return "Ok";

                }

                // Chiudi il fileInputStream quando hai finito
                fileInputStream.close();
            } catch (IOException e) {
                // Gestisci l'eccezione se il dispositivo non è connesso
                System.out.println("Device not connected. Waiting...");
                try {
                    Thread.sleep(1000); // Attendi per 1 secondo prima di ritentare
                } catch (InterruptedException ex) {
                    ex.printStackTrace();
                }
            }
        }


    }
}

When I get the barcode nothing is displayed and printed. When I click on the submit button, I see the barcode printed in the terminal.
What I would like is that every time I get a barcode, it is added and displayed in the table until I press submit. How can I do that?

[Lou Hamers]

Late reply I know, I guess you've moved on by now (I missed this post or it was too complex to respond to when I saw it), but did you get any further with this?

First I would say, don't call stage.showAndWait(), just call show(). JavaDoc should help clear up why: https://docs.oracle.com/javase/8/javafx/api/javafx/stage/Stage.html#showAndWait

The double while(true) loops are not a great idea - I don't think you want the outer while loop at all. And your fileInputStream.close() method never gets called at the end, which is bad - after the return "Ok";, the method is left entirely.
For the inner loop you can do this instead, this is using something called a try-with-resources:

try (FileInputStream fileInputStream = new FileInputStream(portaSeriale)) {
    byte[] buffer = new byte[1024];
    int bytesRead;
    while ((bytesRead = fileInputStream.read(buffer)) != -1) {
        String dati = new String(buffer, 0, bytesRead).strip();
        tableView.getItems().add(new ReadData(dati, 1));
        System.out.println(dati);
        return "Ok";
    }
} catch (IOException e) {
    System.out.println("Device not connected. Waiting...");
    try {
        Thread.sleep(1000); //<---- Be aware this is going to BLOCK the JavaFX application thread, which will prevent the UI from updating and may cause the UI to "freeze" - you might want a different approach: 'fail' and make the user click the button again...
    } catch (InterruptedException ex) {
        ex.printStackTrace();
    }
}

I would call the second class BarCodeReadingService (or at least something that's a noun instead of a verb type name) and refactor things so that all JavaFX stuff like TableView/TableColumn/Button/BorderPane/VBox etc. are in a method (displayCode() or something) in the "Main" class. Then that method would call the service class to read the barcode. The "service" class would focus ONLY on the barcode/USB concerns, to keep that decoupled from your UI code (that could be a conversation in itself but I'll just say it's considered a good practice, and that would make it independently testable without a UI being involved). The 'service' method would just have the stuff I pasted refactored above.

Last thing, you don't want to have potentially never ending loops or anything that might take a long time to execute run on the JavaFX thread, because that thread does rendering and updates for the UI itself. If it's locked in a never-ending loop or a very slow method, it never gets a chance to update the UI view, so it'll appear to "freeze".