可能重复：
JProgressBar 不会更新
所以我试图显示一个用 Java 下载的文件的下载进度。我可以将当前百分比作为字符串输出到控制台，但是当我尝试更新 UI 时，它会冻结，直到下载完成。
public void downloadFile(String fileName) {
try {
long startTime = System.currentTimeMillis();
System.out.println("Connecting to site...\n");
URL url = new URL("http://assets.minecraft.net/"+fileName+"/minecraft.jar");
URLConnection connection = url.openConnection();
try (InputStream reader = url.openStream(); FileOutputStream writer = new FileOutputStream("minecraft.jar")) {
byte[] buffer = new byte[153600];
int totalBytesRead = 0;
int bytesRead = 0;
int totalSize = connection.getContentLength();
jProgressBar1.setMaximum(totalSize);
System.out.println("Downloading\n");
while ((bytesRead = reader.read(buffer)) > 0) {
writer.write(buffer, 0, bytesRead);
buffer = new byte[153600];
totalBytesRead += bytesRead;
jProgressBar1.setValue(totalBytesRead);
System.out.println(totalBytesRead*100/totalSize+"% complete");
}
long endTime = System.currentTimeMillis();
System.out.println("Done. " + (new Integer(totalBytesRead).toString()) + " bytes read (" + (new Long(endTime - startTime).toString()) + " millseconds).\n");
}
}
catch (MalformedURLException e) {
}
catch (IOException e) {
}
}
我在某处读到您需要使用另一个线程，但我无法成功地做到这一点。