Push notification Android后端的谷歌云消息

我制作了一个接收推送通知的应用程序。当我使用以下java代码向计算机上的发送请求时，会发送和接收通知：

public static void main(String[] args) throws IOException {
    String value = "Kent Arne Bjerke har blitt med på din event";

    String url = "https://android.googleapis.com/gcm/send";
    URL obj = new URL(url);
    HttpsURLConnection con = (HttpsURLConnection) obj.openConnection();

    //add reuqest header
    con.setRequestMethod("POST");
    con.setRequestProperty("Authorization", "key=xxxxxxxxxxxxxxx");
    con.setRequestProperty("Sender", "id=xxxxxxxxxx");

    String urlParameters = "collapse_key=score_update&time_to_live=108&delay_while_idle=1&data.message=" + value + "&registration_id=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";

    // Send post request
    con.setDoOutput(true);
    DataOutputStream wr = new DataOutputStream(con.getOutputStream());
    wr.writeBytes(urlParameters);
    wr.flush();
    wr.close();

    int responseCode = con.getResponseCode();
    System.out.println("\nSending 'POST' request to URL : " + url);
    System.out.println("Post parameters : " + urlParameters);
    System.out.println("Response Code : " + responseCode);

    BufferedReader in = new BufferedReader(
            new InputStreamReader(con.getInputStream()));
    String inputLine;
    StringBuffer response = new StringBuffer();

    while ((inputLine = in.readLine()) != null) {
        response.append(inputLine);
    }
    in.close();

    //print result
    System.out.println(response.toString());
}

在我的计算机上本地测试了这段代码之后，我想在我的google app engine服务器上实现这段代码。我复制了代码，并从google app engine端点方法调用了它。然后我得到了这个错误：

{
 "error": {
  "errors": [
   {
    "domain": "global",
    "reason": "backendError",
    "message": "java.lang.ClassCastException: com.google.apphosting.utils.security.urlfetch.URLFetchServiceStreamHandler$Conne     ction cannot be cast to javax.net.ssl.HttpsURLConnection"
   }
  ],
  "code": 503,
  "message": "java.lang.ClassCastException: com.google.apphosting.utils.security.urlfetch.URLFetchServiceStreamHandler$Connection cannot be cast to javax.net.ssl.HttpsURLConnection"
 }
}

如果我理解正确，则不允许使用此方法调用

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我正在寻找一种很好的方法来调用Android的谷歌云消息，并从我的服务器而不是客户端发送推送通知。我必须向多个接收者发送推送通知，因此它必须是异步的。

我通过使用以下代码从后端服务器发送推送通知找到了解决方案：Sender Sender=new SenderAPI_KEY；Message msg=new Message.Builder.addDatamessage，Message.build；结果=sender.sendmsg，sender_id，5；请你可以给它作为一个答案，如果它为你工作，并标记为回答。