Apache's HttpClient can be used to send HTTP requests from the client to the server,

The steps to send GET and POST requests using Apache's HttpClient are as follows:
1. Use the helper HttpClients to create a CloseableHttpClient object.
2. Create an HttpGet or HttpPost instance based on the type of HTTP request to be sent.
3. Use the addHeader method to add request headers, such as User-Agent, Accept-Encoding and other parameters.
4. For the POST request, create a NameValuePair list and add all the form parameters. Then fill it into the HttpPost entity.
5. Obtain CloseableHttpResponse instance by executing this HttpGet or HttpPost request
6. Get the status code, error message, response page, etc. from this CloseableHttpResponse instance.
7. Finally, close the HttpClient resource.

    public String doPost(String url, String params) {
        String result = "";
        CloseableHttpClient httpclient = null;
        CloseableHttpResponse response = null;
        HttpServletRequest request = ((ServletRequestAttributes) RequestContextHolder.getRequestAttributes()).getRequest();
        HttpSession session = request.getSession();
        if (session != null) {
            httpclient = (CloseableHttpClient) session.getAttribute("httpclient");
        }
        if (httpclient == null) {
            httpclient = HttpClients.createDefault();
        }
        try {
            HttpPost httppost = new HttpPost(url);
            httppost.setHeader("accept", "*/*");
            httppost.setHeader("connection", "Keep-Alive");
            httppost.setHeader("User-Agent", "Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/39.0.2171.71 Safari/537.36");

            if (params != null && !"".equals(params)) {
                MultipartEntityBuilder reqEntity = MultipartEntityBuilder.create();
                reqEntity.setCharset(Charset.forName("utf-8"));
                String[] nameAndValue = params.split("&");
                for (String s : nameAndValue) {
                    String[] keyAndvalue = s.split("=",2);
                    //String[] keyAndvalue = s.split("=");
                    StringBody value = new StringBody("", ContentType.TEXT_PLAIN);
                    if(keyAndvalue.length == 2) {
                        value = new StringBody(keyAndvalue[1], Charset.forName("utf-8"));
                        //value = new StringBody(keyAndvalue[1],  ContentType.TEXT_PLAIN);
                    }
                    reqEntity.addPart(keyAndvalue[0], value);
                }
                HttpEntity httpEntity = reqEntity.build();
                httppost.setEntity(httpEntity);
            }
            response = httpclient.execute(httppost);
            HttpEntity resEntity = response.getEntity();
            if(resEntity != null) {
                result = EntityUtils.toString(resEntity, "utf-8");
            }
            EntityUtils.consume(resEntity);
            //if (url.endsWith("center/login") || url.endsWith("#forgetPswd") || url.endsWith("#register")) {
                session.setAttribute("httpclient", httpclient);
            //}

                //2017-08-24 Solve the problem that the request to return the member who is not logged in due to the expiration of the session
                if(StringUtils.isNotBlank(result)){
                    boolean isJson = Common.isJson(result);
                                         //Some requests are not in json format, such as hospital dynamics
                    if(isJson){
                        JSONObject js = JSONObject.fromObject(result);
                                                 //Some results did not return code
                        if(js.has("code")){
                            if(ErrorCode.LS_ILLEGAL_LOGIN.equals(js.getString("code"))){
                                log.info("[This request returns the member who is not logged in]"+js.toString());
                                                                 //Put the request information into the cache
                                RCacheEnTity rCacheEnTity = new RCacheEnTity(url,params,new Date());
                                CachePool.getInstance().putCacheItem("RC", rCacheEnTity);
                                String openId = (String) request.getSession().getAttribute("openId");
                                log.info("[Re-login openID]"+openId);
                                                                 //Re-login
                                String cxdl = doPost(WechatContext.getInstance().getServerUrl() + "center/wechatLogin", "username=" + openId);
                                                                 //Retrieve the last request information
                                CacheItem cacheItem = (CacheItem) CachePool.getInstance().getCacheItem("RC");
                                RCacheEnTity rCacheEnTity2 = (RCacheEnTity) cacheItem.getEntity();
                                log.info("[Re-requested URL]"+rCacheEnTity2.getUrl());
                                                                 //Resend the last request
                                String cxqq = doPost(rCacheEnTity2.getUrl(),rCacheEnTity2.getParams());
                                JSONObject cx = JSONObject.fromObject(cxqq);
                                                                 //After the request is successful, the last request information in the cache will be removed
                                if(ErrorCode.LS_SUCCESS.equals(cx.getString("code"))){
                                                                         //If the request is successful, remove the cache
                                    CachePool.getInstance().removeCacheItem("RC");
                                    result=cxqq;
                                }else{
                                    CachePool.getInstance().removeCacheItem("RC");
                                }
                            }
                        }
                    }
                }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (response != null) {
                    response.close();
                }
                // httpclient.close();
            } catch (IOException e1) {
                e1.printStackTrace();
            }
        }

        return result;
    }