How to bind ProgressBar ?

Question

Hello ,
I want to use ProgressBar to indicate progress how much data are downloaded ;
How to bind ProgressBar with property and then to setProgress() method with this property.

Answer 1

You had two problems in your code. First, the input stream "bis" had already been closed by the time the Task ran, thanks to the try-with-resources block closing everything for you. Second, the updateProgress was always producing values that would result in -1 (or a negative number) being produced for the progress.
Instead, you should open the streams (try-with-resources) within the task, fully in the background thread. And, you should pass the raw values into updateProgress instead of trying to compute a value between 0 and 100, and just let the updateProgress method do it for you.
import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.net.URL;
import javafx.application.Application;
import javafx.concurrent.Task;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.geometry.Insets;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.ProgressBar;
import javafx.scene.control.TextField;
import javafx.scene.layout.HBox;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;
* @author idle
public class YourDownloader extends Application {
    private final HBox hBox = new HBox();
    private final VBox vBox = new VBox();
    ProgressBar progress = new ProgressBar(0.01);
    public static void main(String[] args) {
        Application.launch(args);
    @Override public void start(Stage primaryStage) {
        primaryStage.setTitle("Your Dounloader");
        Group root = new Group();
        Scene scene = new Scene(root, 500, 250);
        final TextField urlTextField = new TextField();
        urlTextField.setPromptText("Add URL here");
        urlTextField.setPrefWidth(scene.getWidth() - scene.getWidth() / 3);
        Button btn = new Button();
        btn.setText("Start Download");
        btn.setOnAction(new EventHandler<ActionEvent>() {
            @Override public void handle(ActionEvent event) {
                try {
                    startDownload(urlTextField.getText());
                } catch (IOException ex) {
                    System.err.println("There is a IOException !!! : " + ex);
        hBox.getChildren().addAll(urlTextField, btn);
        hBox.setPadding(new Insets(10, 5, 5, 10));
        hBox.setSpacing(20);
        vBox.getChildren().addAll(hBox, progress);
        root.getChildren().add(vBox);
        primaryStage.setScene(scene);
        primaryStage.show();
    public void startDownload(final String stringUrl) throws IOException {
        final Task<Void> task = new Task<Void>() {
            @Override public Void call() throws Exception {
                URL url = new URL(stringUrl);
                String fileName = url.getFile();
                fileName = fileName.substring(fileName.lastIndexOf('/') + 1);
                try (BufferedInputStream bis = new BufferedInputStream(url.openStream());
                     FileOutputStream fos = new FileOutputStream(fileName);
                     BufferedOutputStream bos = new BufferedOutputStream(fos, 1024))
                    // buffer of the downloaded data
                    byte[] data = new byte[1024];
                    int read = 0, totalRead = 0;
                    long contentLength = url.openConnection().getContentLength();
                    while ((read = bis.read(data, 0, 1024)) > 0) {
                        totalRead += read;
                        bos.write(data, 0, read);
                        updateProgress(totalRead, contentLength);
                    return null;
        progress.progressProperty().bind(task.progressProperty());
        new Thread(task).start();
}