HttpClient httpClient = HttpClientBuilder.create()
        .setConnectionManager(connManager)
        .build();

String url = "https://" + domain + urlSuffix;
HttpPost httpPost = new HttpPost(url);
RequestConfig requestConfig = RequestConfig.custom().setSocketTimeout(readTimeoutMs).setConnectTimeout(connectTimeoutMs).build();
httpPost.setConfig(requestConfig);

StringEntity postEntity = new StringEntity(data, "UTF-8");
httpPost.addHeader("Content-Type", "text/xml");
httpPost.addHeader("User-Agent", USER_AGENT + " " + config.getMchID());
httpPost.setEntity(postEntity);

HttpResponse httpResponse = httpClient.execute(httpPost);
HttpEntity httpEntity = httpResponse.getEntity();
return EntityUtils.toString(httpEntity, "UTF-8");

为什么HttpClient最后没有关闭，而且每次request都会创建一个HttpClient对象（是否需要使用CloseableHttpClient），创建HttpClient是一个很耗费资源的过程，这样在高并发下会不会出现fullgc，如果来不及回收的情况下，系统直接挂掉

官网demo下载地址：https://pay.weixin.qq.com/wiki/doc/api/micropay_sl.php?chapter=11_1