java - getContentLength() 是否下载整个文件？

Question

这是我的下载图像宽度百分比代码[Java]:

URL url = new URL(imageUrl);
    OutputStream os;
    URLConnection connection = url.openConnection();
    connection.connect();
    int fileLenth = connection.getContentLength();
    try (InputStream is = url.openStream()) {
        os = new FileOutputStream(destinationFile);
        byte[] b = new byte[2048];
        int length;
        int count = 0;
        double sumCount = 0.0;
        while ((length = is.read(b)) != -1) {
            os.write(b, 0, length);

            sumCount += count;
            if (fileLenth > 0) {
                System.out.println("Percentace: " + (sumCount / fileLenth * 100.0) + "%");
            }
        }
    }
    os.close();

我想知道我什么时候使用:

URLConnection connection = url.openConnection();
connection.connect();
int fileLenth = connection.getContentLength();

文件是否已下载？如果这是真的，文件将被下载两次，这不好你能帮我获得最佳表现吗？谢谢

Answer 1

getContentLength() 方法不下载文件，它只是返回content-length header (如果有的话)的值，more details here