在更新JProgressBar的同时下载文件 [英] Download a file while also updating a JProgressBar
问题描述
我尝试过不同方法的音调来让它工作，但是它们不能与进度条一起工作，或者不按照我想要的方式工作。
I have tried tones of different methods to get this to work but they either don't work with a progress bar or don't work the way I would like it to.
我已经创建了一个带有进度条的新窗口，需要创建一个方法，允许我下载一个文件，同时更新一个 JProgressBar 。有一个Apache Commons方法非常容易用于下载文件，但它似乎与 JProgressBar 的兼容。
I have already created a new window with a progress bar and need to create a method which would allow me to download a file while also updating a JProgressBar. There is an Apache Commons method that is extremely easy to use for downloading files but it doesn't seem to be compatible with JProgressBar's.
我在另一个线程中运行时也遇到麻烦， SwingUtilities.invokeLater 似乎没有更新到进度条，但它的运行方式我可以把它打印到控制台。我甚至尝试了 progressBar.repaint（）方法。
I have also had trouble when running this in another thread, SwingUtilities.invokeLater doesn't seem to update to progress bar, but it does run as I can get it to print to the console. I have even tried the progressBar.repaint() method.
所以我想要的是一种可以下载文件，同时更新 JProgressBar 以反映下载的状态。
So what I would like is a method that can download a file while also updating a JProgressBar to reflect the status of the download.
提前感谢！
Keir
Thanks in advance! Keir
推荐答案
根据这篇文章，我可以建议你要写一个下载类，可以轻松更新进度条。
Based on this article, I can suggest you to write a Download class, which can update a progress bar easily.
这是下载类：
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，这个下载类有一些特定的字段，如 size 和已下载。
As you can see, this Download class has got some specific fields like size and downloaded.
在某些其他方法中，您可以写：
In some other method you could write:
JProgressBar j = new JProgressBar(0,download.getSize());
此后，您可以启动一个新的线程 ，它会以一定的间隔更新您的进度条，例如每10 ms，
After this you could start a new Thread, which does update your progress bar at a certain interval, like every 10 ms, with
j.setValue(download.getDownloaded());
希望这可以帮助你。
这篇关于在更新JProgressBar的同时下载文件的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
