HttpURLConnection - 为什么只有在我们从连接读取时才发送请求

Question

为什么当我们尝试从连接中读取请求有效负载发送到请求的内容时。如果是connection.getResponseCode（）; 如果存在，请求由服务器接收，但如果它不存在，则请求未到达/正在发送。

如果连接响应代码在下面评论，它甚至不会抛出任何异常。

这基于Java 8。

            HttpURLConnection connection = null;
        URL url=new URL("http://...");
        connection = (HttpURLConnection) url.openConnection();
        String request="{\"language\":\"english\"}";
        connection.setDoOutput(true);
        connection.setInstanceFollowRedirects(false);
        connection.setRequestMethod("PUT");
        connection.setConnectTimeout(500);
        connection.setReadTimeout(300);

        connection.setRequestProperty("Content-Type", "application/json");

        outputStream = connection.getOutputStream();

        byte[] payload = request.getBytes();
        outputStream.write(payload);
        outputStream.flush();
        outputStream.close();

        //If commented request is not reaching server controller
        //if uncommented , request is reaching
        connection.getResponseCode();