Not in GZIP format报错求助?报错

现在根据URLConnection访问时遇到了这样一个问题，运行程序时会偶尔报Not in GZIP format，这个问题不是经常出现，是偶尔会出现，而且没有规律。

代码如下：

public static Serializable sendRequest(String servlet_url, Serializable obj)  throws Exception  {
    URL url = new URL(servlet_url);
     
    HttpURLConnection con = (HttpURLConnection)url.openConnection();
     
    con.setDoInput(true);
    con.setDoOutput(true);
    con.setUseCaches(false);
    con.setRequestProperty("Content-Type", "application/octet-stream");
 
    writeZIPObject(con.getOutputStream(), obj);
 
    Serializable reply = null;
    reply = (Serializable)readZIPObject(con.getInputStream());
 
    con.disconnect();
 
    Serializable result = reply.getData();
    if (result instanceof Exception) {
        throw ((Exception)result);
    }
 
    ...
 
  }
 
public static Serializable readZIPObject(InputStream in) throws IOException, ClassNotFoundException {
    BufferedInputStream buffer = new BufferedInputStream(in);
    GZIPInputStream gi = new GZIPInputStream(buffer);
    ObjectInputStream oi = new ObjectInputStream(gi);
 
    Serializable obj = (Serializable) oi.readObject();
 
    oi.close();
    gi.close();
    buffer.close();
    in.close();
    return obj;
}
 
public static void writeZIPObject(OutputStream out, Serializable obj) throws IOException {
    BufferedOutputStream buffer = new BufferedOutputStream(out);
    GZIPOutputStream go = new GZIPOutputStream(buffer);
    ObjectOutputStream oo = new ObjectOutputStream(go);
 
    oo.close();
    go.close();
    buffer.close();
    out.close();
}

现在在程序中报这样一个错：
java.io.IOException: Not in GZIP format
at java.util.zip.GZIPInputStream.readHeader(Unknown Source)
at java.util.zip.GZIPInputStream.<init>(Unknown Source)
at java.util.zip.GZIPInputStream.<init>(Unknown Source)
...

报错代码是GZIPInputStream gi = new GZIPInputStream(buffer);

我已经查了网上很多种解决方法可尝试后发现都没有解决，值得注意的是现在程序中传给servlet_url的是一个HTTPS的URL，以前为HTTP时貌似是没有问题的。

请教那位大神遇到过这种问题帮忙回答下