StreamUtils

public static String getContentDisposition(Response response, String filename) throws Exception {
    String disposition = "attachment; ";
    if (asciiEncoder.canEncode(filename))
        disposition += "filename=\"" + filename + "\"";
    else {
        String encodedFilename = urlEncoder.encode(filename, response.encoding);
        disposition += "filename*=" + response.encoding + "''" + encodedFilename + "; filename=\"" + encodedFilename + "\"";
    }

    return disposition;
}

public static void streamFileToResponse(Response response, File file, String filename, String mimeType, int bufferSize, int maxBytesPerSecond) throws Exception {
    FileInputStream fis = null;
    BufferedInputStream bs = null;
    try {
        fis = new FileInputStream(file);
        bs = new BufferedInputStream(fis, bufferSize);
        prepareResponseStreamForFile(response, filename, file.length(), mimeType);
        channelStreamToResponse(response, bs, bufferSize, maxBytesPerSecond);
    } finally {
        if (bs != null)
            bs.close();
        if (fis != null)
            fis.close();
    }
}

public static void prepareResponseStreamForFile(Response response, String filename, long length, String mimeType) throws Exception {
    response.out.reset();
    response.contentType = mimeType;
    response.setHeader("Content-Disposition", getContentDisposition(response, filename));
    response.setHeader("Content-Length", String.valueOf(length));
}

public static void channelStreamToResponse(Response response, InputStream inputStream, int bufferSize, int maxBytesPerSecond) throws Exception {
    InputStream is = null;
    try {
        is = new ThrottledInputStream(inputStream, maxBytesPerSecond);
        byte[] buf = new byte[bufferSize];
        int readBytesLen = 0;
        response.out.reset();
        int flushCnt = 0;

        while ((readBytesLen = is.read(buf)) > 0) {
            if (readBytesLen != bufferSize)
                response.writeChunk(Arrays.copyOf(buf, readBytesLen));
            else
                response.writeChunk(buf);

            if (flushCnt++ > 7 || readBytesLen <= 0) {
                response.out.flush();
                flushCnt = 0;
            }
        }

        response.out.flush();
    } catch (Exception ex) {
        response.out = null;
        System.gc();
        throw ex;
    } finally {
        if (is != null)
            is.close();
        if (inputStream != null)
            inputStream.close();
    }
}