java - Android 部分下载的文件报告错误的文件大小

Question

我正在整理一些代码以从 Android 中的 HTTP 地址下载文件。如果中途下载失败，我想支持下载恢复。

我在开始下载时得到的输出如下:

起始大小为 0停止尺寸 12333416起始尺码 12333416停止大小 16058200起始尺码 3724784

我不明白为什么在第一次恢复后，部分下载文件的后续文件大小读数不匹配。

提前致谢!

public void download(String source, String target) throws IOException {
    BufferedOutputStream outputStream = null;
    InputStream inputStream = null;

    try {
        File targetFile = new File(target);
        currentBytes = targetFile.length();

        Log.i(TAG, "Start size " + String.valueOf(currentBytes));
        outputStream = new BufferedOutputStream(new FileOutputStream(targetFile));

        // create the input stream
        URLConnection connection = (new URL(source)).openConnection();
        connection.setConnectTimeout(mCoTimeout);
        connection.setReadTimeout(mSoTimeout);

        inputStream = connection.getInputStream();
        inputStream.skip(currentBytes);

        // calculate the total bytes
        totalBytes = connection.getContentLength();

        byte[] buffer = new byte[1024];
        int bytesRead;

        while ((bytesRead = inputStream.read(buffer)) > 0) {
            // write the bytes to file
            outputStream.write(buffer, 0, bytesRead);
            outputStream.flush();

            currentBytes += bytesRead;
        }
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        if (outputStream != null) {
            // close the output stream
            outputStream.flush();
            outputStream.close();
        }

        if (inputStream != null) {
            // close the input stream
            inputStream.close();
        }

        Log.i(TAG, "Stop size " + String.valueOf(currentBytes));
    }
}

Answer 1

你做错了两件事:

1. 要恢复下载到文件，您应该附加而不是重写文件。为输出流使用特殊的构造函数:

   FileOutputStream(targetFile, true)

2. 要从服务器请求部分文件，您应该使用 HTTP 1.1 属性“Range”。你可以这样做:

   HttpURLConnection httpConnection = (HttpURLConnection) 连接；connection.setRequestProperty("Range", "bytes="+ currentBytes + "-");