下载文件时更新JProgressBar

Question

我正在尝试创建一个安装程序，该程序正在为我的程序下载一些文件。 在下载文件时，我希望更新我的JProgressBar，但是以某种方式，当我使用代码时，程序冻结了。

我的下载无效

    public static boolean download() {
    URL url = null;
    try {
         url = new URL("http://(domainnameremoved).de/download/1408/");
    } catch (MalformedURLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    final Download download = new Download(url);
    Start.progressBar.setMinimum(0);
    Start.progressBar.setMaximum(download.getSize());

    SwingUtilities.invokeLater(new Runnable() {
        public void run() {
            while(!(download.getStatus() == 2)||!(download.getStatus() == 3)||!(download.getStatus() == 4)) {
                Start.progressBar.setValue(download.getDownloaded());
            }
            }

    });

    if(download.getStatus() == 2) {
        return true;
    } else {
        return false;
    }


}

我的下载课程（不是从我这里下载的，我是在互联网上找到的）

public 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();
}

public int getDownloaded() {
    return this.downloaded;
}

// 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();
}
}

您知道为什么我的程序只是冻结，为什么ProgressBar没有更新吗？

Answer 1

如果您使用一些线程安全的自定义外观，可能会出现问题。 如果使用默认的外观，则不会发生。 在您的情况下，可能的问题是，当某些URL套接字打开时会阻塞主线程。 您调用SwingUtilities.invokeLater ...更新进度条，此SwingUtils.invokLater（）将等待直到该Web套接字关闭。 您可以使用简单的方法：

      new Thread(new Runnable(){ public void run(){ do here what you want in your case...}}).start(); 

或者您使用更复杂的SwingWorker对象。 同样，您也可以将Thread.sleep（）方法的值在1到5毫秒之间，分别用于run（）方法和Download类以及download方法，以优化处理器压力。