JProgressBar doesn't update during download

Question

Using a swing button, I'm trying to download an html file and write it to a new html file, while doing a progress bar. When I click the button, my program seems to freeze until the download finishes, and then the progress bar is suddenly 100%. I'm not quite sure how to fix this problem as I am new to java.

private void jButton2MouseReleased(java.awt.event.MouseEvent evt) {
    try {    
        URL oracle = new URL("http://mywebsite.com");
        URLConnection yc = oracle.openConnection();
        BufferedReader in = new BufferedReader(new InputStreamReader(yc.getInputStream()));
        String inputLine;
        String input_path = "d:/website/updatedsite.html";
        WriteFile data = new WriteFile(input_path, false);
        int length = yc.getContentLength();
        int current = 0;
        jProgressBar1.setMaximum(length);
        jProgressBar1.setValue(0);
        while ((inputLine = in.readLine()) != null) {
            data.writeToFile(inputLine);
            int i = 0;
            for (i = 0; i < length; i++) {
                jProgressBar1.setValue(i);
            }
        }
        in.close();
    }
    catch (java.io.IOException e) { 
    JOptionPane.showMessageDialog(Frame1.this, "Error " + e.getMessage());
}

}

Answer 1

This is because you're both downloading and updating the progress bar in the same thread - that's why the gui gets actually updated AFTER the download is finished.

Use a separate worker thread for downloading like explained here and it should work.