ProgressBar in Javafx shows only state 0 and 100% while copying file - multithreading

Question

How to fix this code using multithreading?
It's working but I need to know how to add a thread to this code, I think that this is why the progress bar not updating progressively!
public void copyfile(ActionEvent event){
try {
File fileIn = new File(filepath);
long length = fileIn.length();
long counter = 0;
double r;
double res=(counter/length);
filename=fieldname.getText();
FileInputStream from=new FileInputStream(filepath);
FileOutputStream to=new FileOutputStream("C:\\xampp\\htdocs\\videos\\"+filename+".mp4");
byte [] buffer = new byte[4096];
int bytesRead=0;
while( (r=bytesRead=from.read(buffer))!= 1){
progressbar.setProgress(counter/length);
counter += r*100;
to.write(buffer, 0, bytesRead);
System.out.println("File is loading!!"+(counter/length));
}
from.close();
to.close();
} catch (Exception e) {
progress.setText("upload is finished!!");
}
}
Can you please post any solution, which helps me?
Thanks for all advices.

Answer 1

There is an example of associating a progress bar with progress of a concurrent task in Oracle's JavaFX 8 concurrency documentation.
import javafx.concurrent.Task;
Task task = new Task<Void>() {
#Override public Void call() {
static final int max = 1000000;
for (int i=1; i<=max; i++) {
if (isCancelled()) {
break;
}
updateProgress(i, max);
}
return null;
}
};
ProgressBar bar = new ProgressBar();
bar.progressProperty().bind(task.progressProperty());
new Thread(task).start();