// 檔案url地址
URL xu = new URL(url);
// 檔名
String name = "";

HttpURLConnection conn = (HttpURLConnection)xu.openConnection();

conn.setRequestProperty("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/86.0.4238.2 Safari/537.36");
conn.setRequestProperty("Origin", "https://www.bilibili.com");
 
conn.setRequestProperty("Referer", "https://www.bilibili.com/video/BV" + bv);
BufferedInputStream input = new BufferedInputStream(conn.getInputStream());

System.out.println("開始下載檔案：" + name);
System.out.println("檔案大小：" + input.available());
File file = new File(name);
if(!file.exists())
{
    file.createNewFile();
 
}
BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(file));

byte[] by = new byte[1024];
int num = 0;
while ((num = input.read(by)) != -1)
{
    for(int j = 0 ; j < num ; j++)
    {
　　　　　// 這裡必須按位元組寫入，否則會出現錯誤
        out.write(by[j]);
    }
}
out.flush();
out.close();
input.close();
System.out.println("檔案下載完成===========================>\n\n\n");