如何让我的java应用程序替换自己？

Question

我正在为我的几个客户编写程序以便不时使用，但它仍然非常简单，我计划在使用它时添加功能。他们知道这一点，并且对计划很好，因为它允许他们更早地使用该程序，即使它比最终版本更基本。

我的问题是，要更新，我将从github存储库下载更新版本的应用程序（作为JAR文件运行），在程序运行时替换该程序，然后重新启动它，作为新版本。此设计还允许我在必要时对更新程序进行更改。是否正在替换程序的可执行JAR，或者我应该采用不同的方法？如果不同的方法可以更好地工作，你们会推荐什么？

另外，我尝试下载文件时经常遇到下载类超时问题。通常，它只是第一次出现问题，因为它通常在第一次尝试后起作用。然而，为了甚至开始下载，用户必须两次运行更新器是非常不方便的。我已在下面的“下载”类中添加了代码。

class Download extends Observable implements Runnable {

    // Max size of download buffer.
    private static final int MAX_BUFFER_SIZE = 1024;

    // 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 final size.
    public int getSize() {
        return size;
    }

    // Get the download's current size
    public int getDownloaded() {
        return downloaded;
    }

    // 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();
    }
}

任何解决这两个问题的方法都是非常受欢迎的。谢谢！