App Engine Endpoint 启用 CORS

回答中描述的问题是我的错（真令人惊讶）。对于在 GAE 上配置 CORS 有问题的其他人：如果 CORS 是开箱即用的。但是为了获得正确的响应，您还必须有正确的请求：

Origin: null
Access-Control-Request-Method: GET

方法必须是以下之一："HEAD", "DELETE", "GET", "PATCH", "POST", "PUT"Origin 实际上可以是任何字符串 - 您将在响应中取回它。“null”是一个特殊的关键字，被翻译成“*”。这是负责生成标头的代码（来自 GAE 来源）：

  public static void allowOrigin(HttpServletRequest request, HttpServletResponse response) {
    String origin = request.getHeader(Headers.ORIGIN);
    // The Origin spec (http://tools.ietf.org/html/draft-abarth-origin-09) allows for the Origin
    // http header value to be "null". This is for cases where a request doesn't have a valid
    // origin; for example, issuing a CORS request from a local file:// rather than a website. In
    // these cases, we'd like to enable CORS to facilitate testing; the mechanism for doing so is
    // to set the Access-Control-Allow-Origin header to '*'.
    origin = NULL_ORIGIN.equals(origin) ? "*" : origin;
    response.setHeader(Headers.ACCESS_CONTROL_ALLOW_ORIGIN, origin);
  }

由于错误的合并 Gradle 文件，我的第二个问题是不稳定的构建。