微信硬件平台的接收微信消息能力，接收图片的时候，download_url下载的文件无法打开，发现文件md5值和原文件md5值不一致，并且文件大小发送变化，报文如下：{"device_id":"gh_b36753c89af2_09cd3e115440cec9","device_type":"gh_b36753c89af2","msg_id":"887006918","msg_type":"set","services":{"wxmsg_file":{"downloadUrl":"http://wxapp.tc.qq.com/202/20303/stodownload?filekey=30340201010420301e020200ca0402535a0410af2a73c0c58201b88285ef67f611272402021000040d00000004627466730000000131&hy=SZ&storeid=32303231303331303137313031383030306139333361363134313832393738656338353730393030303030306361&bizid=1023","md5":"71093817c7f68eb70e90346a157b4e50","name":"80a99f59f472b84942ce20c7ed8f850e.jpg","size":3800,"type":"jpg"},"wxmsg_image":{"downloadUrl":"http://wxapp.tc.qq.com/202/20303/stodownload?filekey=30340201010420301e020200ca0402535a0410af2a73c0c58201b88285ef67f611272402021000040d00000004627466730000000131&hy=SZ&storeid=32303231303331303137313031383030306139333361363134313832393738656338353730393030303030306361&bizid=1023","md5":"71093817c7f68eb70e90346a157b4e50","name":"80a99f59f472b84942ce20c7ed8f850e.jpg","size":3800,"type":"jpg"}},"user":"oleOTjpW_qLjx-oF0B0L91ieMVL4"}

但是该图片是有5,755字节但是下载时候完全不对，并且下载后根本打不开 我下载方式方式代码如下

public static void downloadFile(String remoteFilePath, String localFilePath) {
    URL urlfile = null;
    HttpURLConnection httpUrl = null;
    BufferedInputStream bis = null;
    BufferedOutputStream bos = null;
    File f = new File(localFilePath);
    try {
        urlfile = new URL(remoteFilePath);
        httpUrl = (HttpURLConnection) urlfile.openConnection();
        httpUrl.connect();
        bis = new BufferedInputStream(httpUrl.getInputStream());
        bos = new BufferedOutputStream(new FileOutputStream(f));
        int len = 2048;
        byte[] b = new byte[len];
        while ((len = bis.read(b)) != -1) {
            bos.write(b, 0, len);
        }
        System.out.println("下载成功");
        bos.flush();
        bis.close();
        httpUrl.disconnect();
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        try {
            bis.close();
            bos.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}