使用Retrofit 请求头设置Range实现下载测速功能全部代码

好的，下面是完整的代码示例：

public class DownloadManager {
    private static final int BUFFER_SIZE = 4096;

    public static void downloadFile(String fileUrl, String saveDir) throws IOException {
        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl("http://www.example.com/")
                .build();
        ApiService apiService = retrofit.create(ApiService.class);

        Call<ResponseBody> call = apiService.downloadFile(fileUrl);
        Response<ResponseBody> response = call.execute();
        if (!response.isSuccessful()) {
            throw new IOException("Failed to download file: " + response.code());
        }

        long fileSize = response.body().contentLength();
        long start = 0;
        long end = fileSize - 1;
        String rangeHeader = "bytes=" + start + "-" + end;
        int bytesRead;
        byte[] buffer = new byte[BUFFER_SIZE];
        long startTime = System.currentTimeMillis();
        InputStream inputStream = response.body().byteStream();
        File file = new File(saveDir, getFileName(fileUrl));
        OutputStream outputStream = new FileOutputStream(file);
        while ((bytesRead = inputStream.read(buffer)) != -1) {
            outputStream.write(buffer, 0, bytesRead);
            end += bytesRead;
            long endTime = System.currentTimeMillis();
            long time = endTime - startTime;
            long speed = (end - start + 1) / time;
            long remainingSize = fileSize - (end - start + 1);
            long remainingTime = remainingSize / speed;
            long totalTime = time + remainingTime;
            System.out.println("Downloaded " + (end - start + 1) + " bytes in " + time + "ms, speed: " + speed + "bytes/ms, remaining time: " + remainingTime + "ms, total time: " + totalTime + "ms");
            start += bytesRead;
            rangeHeader = "bytes=" + start + "-" + end;
            call = apiService.downloadFile(fileUrl, rangeHeader);
            response = call.execute();
            inputStream = response.body().byteStream();
        }
        outputStream.close();
        inputStream.close();
        System.out.println("File downloaded at: " + file.getAbsolutePath());
    }

    private static String getFileName(String fileUrl) {
        int index = fileUrl.lastIndexOf("/");
        return fileUrl.substring(index + 1);
    }
}

在上述代码中，我们通过 Retrofit 发送了一个 Range 请求头来下载文件的前几个字节，并计算下载速度和剩余时间。然后在循环中，根据上一次下载的结束位置来发送新的 Range 请求头，实现多次下载，最终将整个文件下载完成。