Java 尝试连接google qpx api时出现Http错误500

我正在尝试与google qpx api（用于航班）集成。 请求是POST，其中包含JSON主体。 我写了以下内容：

    Head request = new Head();
    Gson gson = new Gson();
    String json = gson.toJson(request);
    System.out.println(json);

    HttpClient httpClient = HttpClientBuilder.create().build();
    try {
        HttpPost post = new HttpPost("https://www.googleapis.com/qpxExpress/v1/trips/search?key=MY_API_KEY");
        StringEntity entity = new StringEntity(json);
        post.setEntity(entity);
        post.addHeader("content-type", "application/json");
        post.addHeader("Accept","application/json");
        HttpResponse  response = httpClient.execute(post);
        System.out.println(response);

    } catch (Exception e) {
        e.printStackTrace();
    }

得到这个错误：

HttpResponseProxy{HTTP/1.1 500 Internal Server Error [Vary: Origin, Vary: X-Origin, Content-Type: application/json; charset=UTF-8, Date: Sat, 08 Aug 2015 06:51:58 GMT, Expires: Sat, 08 Aug 2015 06:51:58 GMT, Cache-Control: private, max-age=0, X-Content-Type-Options: nosniff, X-Frame-Options: SAMEORIGIN, X-XSS-Protection: 1; mode=block, Server: GSE, Alternate-Protocol: 443:quic,p=1, Transfer-Encoding: chunked] org.apache.http.client.entity.DecompressingEntity@4de5031f}

---

有人能帮忙吗？

如果有人感兴趣，问题是JSON请求中的“切片”必须是一个列表

应该是这样的：

 {
  "request": {
    "passengers": {
      "kind": "qpxexpress#passengerCounts",
      "adultCount": 1
    },
    "slice": [
      {
        "kind": "qpxexpress#sliceInput",
        "origin": "TLV",
        "destination": "JFK",
        "date": "2015-09-01"
      }
    ],
    "solutions": 1
  }
}