带有HTTP上载的Java ProgressBar不会更新

Question

I want my jProgressBar to update its value during HTTP File Upload . I'm new to Java and I'm not sure I'm doing the right things, here's my code:

private static final String Boundary = "--7d021a37605f0";

public void upload(URL url, File f) throws Exception
{
    HttpURLConnection theUrlConnection = (HttpURLConnection) url.openConnection();
    theUrlConnection.setDoOutput(true);
    theUrlConnection.setDoInput(true);
    theUrlConnection.setUseCaches(false);
    theUrlConnection.setChunkedStreamingMode(1024);

    theUrlConnection.setRequestProperty("Content-Type", "multipart/form-data; boundary="
            + Boundary);

    DataOutputStream httpOut = new DataOutputStream(theUrlConnection.getOutputStream());


        String str = "--" + Boundary + "\r\n"
                   + "Content-Disposition: form-data;name=\"file1\"; filename=\"" + f.getName() + "\"\r\n"
                   + "Content-Type: image/png\r\n"
                   + "\r\n";

        httpOut.write(str.getBytes());

        FileInputStream uploadFileReader = new FileInputStream(f);
        int numBytesToRead = 1024;
        int availableBytesToRead;
        jProgressBar1.setMaximum(uploadFileReader.available());
        while ((availableBytesToRead = uploadFileReader.available()) > 0)
        {
            jProgressBar1.setValue(jProgressBar1.getMaximum() - availableBytesToRead);
            byte[] bufferBytesRead;
            bufferBytesRead = availableBytesToRead >= numBytesToRead ? new byte[numBytesToRead]
                    : new byte[availableBytesToRead];
            uploadFileReader.read(bufferBytesRead);
            httpOut.write(bufferBytesRead);
            httpOut.flush();
        }
        httpOut.write(("--" + Boundary + "--\r\n").getBytes());

    httpOut.flush();
    httpOut.close();

    // read & parse the response
    InputStream is = theUrlConnection.getInputStream();
    StringBuilder response = new StringBuilder();
    byte[] respBuffer = new byte[4096];
    while (is.read(respBuffer) >= 0)
    {
        response.append(new String(respBuffer).trim());
    }
    is.close();
    System.out.println(response.toString());
}

Is this line jProgressBar1.setValue(jProgressBar1.getMaximum() - availableBytesToRead); correct ?

Answer 1

Something like one in every 30 questions tagged java here has the same solution as yours. You are doing all your work inside an event handler, which means that it's happening on the Event Dispatch Thread -- and blocks all further GUI updates until it's over. You must use a SwingWorker and delegate your work to it.

Answer 2

I second @Marko Topolnic's suggestion of using a SwingWorker , Have a look at these useful links to get you further on Howto ,

1. How to Use Progress Bars
2. Concurrency in Swing
3. Worker Threads and SwingWorker

and an example by @trashgod.