Java 发送GCM通知时发生IOException

我正在尝试向GCM服务器发送一些JSON通知，我得到了这个错误列表

Response Code: 400
java.io.IOException: Server returned HTTP response code: 400 for URL: https://gcm-http.googleapis.com/gcm/send
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
        at java.lang.reflect.Constructor.newInstance(Unknown Source)
        at sun.net.www.protocol.http.HttpURLConnection$10.run(Unknown Source)
        at sun.net.www.protocol.http.HttpURLConnection$10.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at sun.net.www.protocol.http.HttpURLConnection.getChainedException(Unknown Source)
        at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(Unknown Source)
        at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source)
        at sun.net.www.protocol.https.HttpsURLConnectionImpl.getInputStream(Unknown Source)
        at controller.Notification.post(Notification.java:181)
        at controller.App.main(App.java:17)
Caused by: java.io.IOException: Server returned HTTP response code: 400 for URL: https://gcm-http.googleapis.com/gcm/send
        at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(Unknown Source)
        at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source)
        at java.net.HttpURLConnection.getResponseCode(Unknown Source)
        at sun.net.www.protocol.https.HttpsURLConnectionImpl.getResponseCode(Unknown Source)
        at controller.Notification.post(Notification.java:179)
        ... 1 more

奇怪的是，只有当我尝试发送到单个设备时才会发生这种情况。如果我尝试使用

registration\u id

字段发送到多个设备，它会起作用。参考称错误400意味着无法解析JSON，但我尝试打印出来，结果似乎很好：

多播发送：（响应代码：200，注册无效）

发送到单个设备：（响应代码：400，以上错误）

要发送到单个或多个设备的函数只有一条不同的行。其中一个将

添加到

字段，另一个将

注册id添加到

字段

obj.put("registration_ids", regIds); // multiple devices
obj.put("to", regId);                // single device

有什么问题吗

编辑：

下面第三行是错误中提到的第181行：

int responseCode = conn.getResponseCode();
System.out.println("Response Code: " + responseCode);
BufferedReader in = new BufferedReader(new InputStreamReader(conn.getInputStream())); // 181

---

我在github上找到了解决方案

似乎只有在响应代码为

200

时才使用

getInputStream（）。否则，应使用
getErrorStream（）

所以把我的代码改成这个就解决了

int responseCode = conn.getResponseCode();
System.out.println("Response Code: " + responseCode);

BufferedReader in = null;
if (responseCode == 200)
    in = new BufferedReader(new InputStreamReader(conn.getInputStream()));
else
    in = new BufferedReader(new InputStreamReader(conn.getErrorStream()));

发送到多个设备时，url的形式是什么？请把它贴在这里
400是错误的请求，并不是说JSON无法解析。
顺便说一句……来自：仅适用于JSON请求。指示无法将请求解析为JSON，或者该请求包含无效字段（例如，在需要数字的位置传递字符串）。响应中描述了确切的失败原因，应该在重试请求之前解决该问题。您是否可以添加断点并检查响应的内容？或者抓住做这件事的例外？
int responseCode = conn.getResponseCode();
System.out.println("Response Code: " + responseCode);
BufferedReader in = new BufferedReader(new InputStreamReader(conn.getInputStream())); // 181

int responseCode = conn.getResponseCode();
System.out.println("Response Code: " + responseCode);

BufferedReader in = null;
if (responseCode == 200)
    in = new BufferedReader(new InputStreamReader(conn.getInputStream()));
else
    in = new BufferedReader(new InputStreamReader(conn.getErrorStream()));