基于

this文章,我建议您编写一个下载类,它可以轻松更新进度条.

这是Download类：

import java.io.*;

import java.net.*;

import java.util.*;

// This class downloads a file from a URL.

class Download extends Observable implements Runnable {

// Max size of download buffer.

private static final int MAX_BUFFER_SIZE = 1024;

// These are the status names.

public static final String STATUSES[] = {"Downloading",

"Paused", "Complete", "Cancelled", "Error"};

// These are the status codes.

public static final int DOWNLOADING = 0;

public static final int PAUSED = 1;

public static final int COMPLETE = 2;

public static final int CANCELLED = 3;

public static final int ERROR = 4;

private URL url; // download URL

private int size; // size of download in bytes

private int downloaded; // number of bytes downloaded

private int status; // current status of download

// Constructor for Download.

public Download(URL url) {

this.url = url;

size = -1;

downloaded = 0;

status = DOWNLOADING;

// Begin the download.

download();

}

// Get this download's URL.

public String getUrl() {

return url.toString();

}

// Get this download's size.

public int getSize() {

return size;

}

// Get this download's progress.

public float getProgress() {

return ((float) downloaded / size) * 100;

}

// Get this download's status.

public int getStatus() {

return status;

}

// Pause this download.

public void pause() {

status = PAUSED;

stateChanged();

}

// Resume this download.

public void resume() {

status = DOWNLOADING;

stateChanged();

download();

}

// Cancel this download.

public void cancel() {

status = CANCELLED;

stateChanged();

}

// Mark this download as having an error.

private void error() {

status = ERROR;

stateChanged();

}

// Start or resume downloading.

private void download() {

Thread thread = new Thread(this);

thread.start();

}

// Get file name portion of URL.

private String getFileName(URL url) {

String fileName = url.getFile();

return fileName.substring(fileName.lastIndexOf('/') + 1);

}

// Download file.

public void run() {

RandomAccessFile file = null;

InputStream stream = null;

try {

// Open connection to URL.

HttpURLConnection connection =

(HttpURLConnection) url.openConnection();

// Specify what portion of file to download.

connection.setRequestProperty("Range",

"bytes=" + downloaded + "-");

// Connect to server.

connection.connect();

// Make sure response code is in the 200 range.

if (connection.getResponseCode() / 100 != 2) {

error();

}

// Check for valid content length.

int contentLength = connection.getContentLength();

if (contentLength < 1) {

error();

}

/* Set the size for this download if it

hasn't been already set. */

if (size == -1) {

size = contentLength;

stateChanged();

}

// Open file and seek to the end of it.

file = new RandomAccessFile(getFileName(url), "rw");

file.seek(downloaded);

stream = connection.getInputStream();

while (status == DOWNLOADING) {

/* Size buffer according to how much of the

file is left to download. */

byte buffer[];

if (size - downloaded > MAX_BUFFER_SIZE) {

buffer = new byte[MAX_BUFFER_SIZE];

} else {

buffer = new byte[size - downloaded];

}

// Read from server into buffer.

int read = stream.read(buffer);

if (read == -1)

break;

// Write buffer to file.

file.write(buffer, 0, read);

downloaded += read;

stateChanged();

}

/* Change status to complete if this point was

reached because downloading has finished. */

if (status == DOWNLOADING) {

status = COMPLETE;

stateChanged();

}

} catch (Exception e) {

error();

} finally {

// Close file.

if (file != null) {

try {

file.close();

} catch (Exception e) {}

}

// Close connection to server.

if (stream != null) {

try {

stream.close();

} catch (Exception e) {}

}

}

}

// Notify observers that this download's status has changed.

private void stateChanged() {

setChanged();

notifyObservers();

}

}

如您所见,这个Download类有一些特定的字段,如大小和下载.

在其他一些方法中你可以写：

JProgressBar j = new JProgressBar(0,download.getSize());

在此之后你可以启动一个新的Thread,它会以一定的间隔更新你的进度条,就像每10毫秒一样

j.setValue(download.getDownloaded());

希望这可以帮到你.