Google Cloud Vision API - 在POST请求中发送base64编码图像

Question

我正在使用Google Vision API制作一个小项目。我想检测在POST请求中发送到API的base64编码图像的面。我的代码基于Google的这个教程：https://cloud.google.com/community/tutorials/make-an-http-request-to-the-cloud-vision-api-from-java。显然可以发送base64编码图像。

这是我的代码：

    File File = new File(args[2]);
    String ImageString;

    FileInputStream fileInputStreamReader = new FileInputStream(File);
    byte[] bytes = new byte[(int)File.length()];
    fileInputStreamReader.read(bytes);
    ImageString = Base64.getEncoder().encodeToString(bytes);

    URL serverUrl = new URL(TARGET_URL + API_KEY); //TARGET_URL = "https://vision.googleapis.com/v1/images:annotate?"
    URLConnection urlConnection = serverUrl.openConnection();
    HttpURLConnection httpConnection = (HttpURLConnection)urlConnection;

    httpConnection.setRequestMethod("POST");
    httpConnection.setRequestProperty("Content-Type", "application/json");

    httpConnection.setDoOutput(true);

    BufferedWriter httpRequestBodyWriter = new BufferedWriter(new
            OutputStreamWriter(httpConnection.getOutputStream()));

    httpRequestBodyWriter.write
            ("{\"requests\":  [{ \"features\":  [ {\"type\": \"FACE_DETECTION\""
                    +"}], \"image\": {\"content\": \"" + ImageString + "\"}]}");
    httpRequestBodyWriter.close();

如您所见，我用字符串替换了“content”字段。我只是不知道我做错了什么。 提前致谢。