Android：将文件上传到服务器后，响应正文中未定义文件扩展名

Question

我正在使用以下代码在聊天应用程序中将文件（pdf，docx，pptx等）从用户发送到用户。

public class UploadFile extends AsyncTask<String, Void, String> {
        protected MessageModel mMessage;
        File file ;
        String mimeType = "";
        public UploadFile(MessageModel msg, File file) {
            super();
            this.mMessage = msg;
            this.file = file;
        }

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
        }

        @Override
        protected String doInBackground(String... params) {

            String responseBodyText = null;
            mimeType = mMessage.getMsgFileType();
            MediaType MEDIA_TYPE = okhttp3.MediaType.parse(mimeType);

            OkHttpClient client = new OkHttpClient();

            try {

        RequestBody req = new okhttp3.MultipartBody.Builder()
                        .setType(okhttp3.MultipartBody.FORM)
                        .addFormDataPart("chatFileUpload", file.getName(), RequestBody.create(MEDIA_TYPE, file)).build();

                Request request = new Request.Builder()

                        .header("Authorization", "Bearer "+Constants.AUTH_TOKEN)
                        .addHeader("User-Agent", Constants.USER_AGENT)
                        .url(urlforFileUpload)
                        .post(req)
                        .build();


                Response response = null;
                response = client.newCall(request).execute();

                if (!response.isSuccessful()) {
                    throw new IOException("Okhttp Error: " + response);

                } else {
                    responseBodyText = response.body().string();
                    Log.d("PrintResponseBody", responseBodyText); // Print the response body here
                }
            } catch (IOException e) {
                e.printStackTrace();

            }

            return responseBodyText;
        }

        @Override
        protected void onPostExecute(String result) {
            super.onPostExecute(result);
            JSONObject msgFiles = new JSONObject();
            if (result != null) {
                try {
                    JSONObject responseObject = new JSONObject(result);
                    msgFiles.put("filename", responseObject.get("fileName"));
                    msgFiles.put("mimetype", responseObject.get("mimetype"));
                    msgFiles.put("filepath", responseObject.get("fileUploadPath"));

                    Log.d("PrintFileUploadPath", String.valueOf(responseObject.get("fileUploadPath")));
                    // Print the response upload file path with file name and extension;

                    //.... do other stuffs....

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

            }

        }
    }

在logcat中，我的扩展名为'undefined'而不是正确的扩展名（.docx，.pptx等）。有人能告诉我哪种行为会引起这种行为吗？它合适吗？如果是，我该如何检查用户从服务器响应中接收哪种类型的文件？

我正在使用调试器的响应示例：

{
"status":"true",
"fileName":"1490691261587.undefined",
"fileUploadPath":"/uploads/chat_upload/1490691261587.undefined",
"mimetype":"file/file",
"msg":"File is uploaded successfully",
"downloadLink":"<a  target=\"_blank\" href=\"/uploads/chat_upload/1490691261587.undefined\">New-Text-Document.txt909.txt</a>"
}

提前致谢。