java - personalizar - Usando la GUI de swing para hacer aparecer una barra de progreso mientras se descarga un archivo

personalizar progressbar java

Question

Esta pregunta ya tiene una respuesta aquí:

• JProgressBar no actualizará 3 respuestas

Actualmente tengo una clase que debería mostrarme un formulario simple mientras descargo un archivo. Está funcionando, pero la barra de progreso no se está actualizando, y solo puedo verla una vez que la descarga haya finalizado. ¿Alguien me puede ayudar?

import java.awt.FlowLayout;
import java.io.*;
import java.net.HttpURLConnection;
import java.net.URL;
import javax.swing.JFrame;
import static javax.swing.JFrame.EXIT_ON_CLOSE;
import javax.swing.JProgressBar;

public class Downloader {

    public Downloader(String site, File file) {
        JFrame frm = new JFrame();
        JProgressBar current = new JProgressBar(0, 100);
        current.setSize(50, 100);
        current.setValue(0);
        current.setStringPainted(true);
        frm.add(current);
        frm.setVisible(true);
        frm.setLayout(new FlowLayout());
        frm.setSize(50, 100);
        frm.setDefaultCloseOperation(EXIT_ON_CLOSE);
        try {
            URL url = new URL(site);
            HttpURLConnection connection
                    = (HttpURLConnection) url.openConnection();
            int filesize = connection.getContentLength();
            float totalDataRead = 0;
            try (java.io.BufferedInputStream in = new java.io.BufferedInputStream(connection.getInputStream())) {
                java.io.FileOutputStream fos = new java.io.FileOutputStream(file);
                try (java.io.BufferedOutputStream bout = new BufferedOutputStream(fos, 1024)) {
                    byte[] data = new byte[1024];
                    int i;
                    while ((i = in.read(data, 0, 1024)) >= 0) {
                        totalDataRead = totalDataRead + i;
                        bout.write(data, 0, i);
                        float Percent = (totalDataRead * 100) / filesize;
                        current.setValue((int) Percent);
                    }
                }
            }
        } catch (IOException e) {
            javax.swing.JOptionPane.showConfirmDialog((java.awt.Component) null, e.getMessage(), "Error",
                    javax.swing.JOptionPane.DEFAULT_OPTION);
        }
    }
}

Answer 1

El suyo es un clásico problema de concurrencia de Swing. La solución es, como siempre, hacer el código de larga ejecución en un hilo de fondo, como se puede encontrar con un SwingWorker.

p.ej,

import java.awt.FlowLayout;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.io.*;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.concurrent.ExecutionException;

import javax.swing.JFrame;
import javax.swing.SwingWorker;

import static javax.swing.JFrame.EXIT_ON_CLOSE;

import javax.swing.JProgressBar;

public class Downloader {

   public Downloader(String site, File file) {
      JFrame frm = new JFrame();
      final JProgressBar current = new JProgressBar(0, 100);
      current.setSize(50, 100);
      current.setValue(0);
      current.setStringPainted(true);
      frm.add(current);
      frm.setVisible(true);
      frm.setLayout(new FlowLayout());
      frm.setSize(50, 100);
      frm.setDefaultCloseOperation(EXIT_ON_CLOSE);
      final Worker worker = new Worker(site, file);
      worker.addPropertyChangeListener(new PropertyChangeListener() {

         @Override
         public void propertyChange(PropertyChangeEvent pcEvt) {
            if ("progress".equals(pcEvt.getPropertyName())) {
               current.setValue((Integer) pcEvt.getNewValue());
            } else if (pcEvt.getNewValue() == SwingWorker.StateValue.DONE) {
               try {
                  worker.get();
               } catch (InterruptedException | ExecutionException e) {
                  // handle any errors here
                  e.printStackTrace(); 
               }
            }

         }
      });
      worker.execute();
   }
}

class Worker extends SwingWorker<Void, Void> {
   private String site;
   private File file;

   public Worker(String site, File file) {
      this.site = site;
      this.file = file;
   }

   @Override
   protected Void doInBackground() throws Exception {
      URL url = new URL(site);
      HttpURLConnection connection = (HttpURLConnection) url
            .openConnection();
      int filesize = connection.getContentLength();
      int totalDataRead = 0;
      try (java.io.BufferedInputStream in = new java.io.BufferedInputStream(
            connection.getInputStream())) {
         java.io.FileOutputStream fos = new java.io.FileOutputStream(file);
         try (java.io.BufferedOutputStream bout = new BufferedOutputStream(
               fos, 1024)) {
            byte[] data = new byte[1024];
            int i;
            while ((i = in.read(data, 0, 1024)) >= 0) {
               totalDataRead = totalDataRead + i;
               bout.write(data, 0, i);
               int percent = (totalDataRead * 100) / filesize;
               setProgress(percent);
            }
         }
      }
      return null;
   }
}