파일 이어받기

private String downloadFile(String urlString, String savePath) {
    URL url;
    InputStream inputStream;
    OutputStream outputStream;
    HttpURLConnection con;

    long fileSize = 0;
    long remains = 0;
    long fileLength = 0;

    try {

        File file = new File(savePath);
        if(!file.exists()) {
            file.createNewFile();
        }
        RandomAccessFile output = new RandomAccessFile(
                                                             file.getAbsolutePath(), "rw");
        fileSize = output.length();
        output.seek(fileSize);

        url = new URL(urlString);
        con = (HttpURLConnection)url.openConnection();
        con.setRequestProperty("Connection", "keep-alive");
        con.setRequestProperty("Range", "bytes=" + String.valueOf(fileSize) + '-');
        con.setConnectTimeout(10000);
        con.setReadTimeout(20000);
        con.connect();

        int length = con.getContentLength();
        remains = length;
        fileLength = remains + fileSize;
        inputStream = con.getInputStream();

        byte data[] = new byte[1024];
        int count;
        int total = 0;
        while((count = inputStream.read(data)) != -1) {
            total += count;            
            output.write(data, 0, count);
        }
        
        output.close();
        inputStream.close();

    } catch (Exception e) {
        //e.printStackTrace();
        return "down fail : " + e.getMessage();
    }

    return "success";
}



* 서버에 따라 이어받기가 안되는 경우도 생김 - 이때 Range의 마지막 지정해야함
예)
con.setRequestProperty("Range", "bytes=" + String.valueOf(fileSize) + '-'
                                                       + String.valueOf(fullSize));
** fullSize는 알아서 구하기~