没有本地代理的Invalid_payload，有代理的Invalid_payload 200？

Question

我正在尝试通过Apache HttpClient从Servlet发送一个简单的Hello World到Slack Webhook。最后，我的servlet将作为JIRA的Webhook并针对“ Jira Server Alerts”不支持的某些事件向Slack发布消息。

现在发生了一些有趣的事情：每当我运行doPost（）方法时，我都会从Slack收到invalid_payload-Reply。但是，如果我使用本地Postman-proxy拦截了请求，则该请求将被接受并发布消息。代理与我的HttpClient有何不同？

@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    final HttpClient hc = HttpClientBuilder.create()
            .setRedirectStrategy(new LaxRedirectStrategy())
//          .setProxy(new HttpHost("localhost", 5555))
            .build();

    final HttpHost target = new HttpHost("hooks.slack.com");
    final HttpEntityEnclosingRequest request = new BasicHttpEntityEnclosingRequest("POST",
        "<Slack Webhook URL>");
    request.setHeader("Content-Type", "application/json");
    request.setEntity(new StringEntity("{ \"text\" : \"Hello World\" }", 
        ContentType.APPLICATION_JSON));

    System.err.println(request.getRequestLine());
    for(Header h : request.getAllHeaders()) {
        System.err.println(h);
    }
    System.err.println(EntityUtils.toString(request.getEntity()));
    System.err.println("------------------------------------------------");

    try {
        final HttpResponse response = hc.execute(target, request);
        System.err.println(response.getStatusLine());
        System.err.println(EntityUtils.toString(response.getEntity()));
    } catch (IOException e) {
        e.printStackTrace();
    }

    resp.setStatus(200);
}