java调用外部API，通过http请求，HttpGet和HttpPost方式实现

public Map<String, Object> h5Pay(HttpServletRequest request, PaymentUser paymentUser) throws IOException {
 
 

//2.调用下单API,接口调用地址
HttpPost httpPost = new HttpPost("www.baidu.com")

//设置请求体（接口必要参数）
Map<String, Object> paramMap = new HashMap<>();
paramMap.put("appid", wxPayConfig.getAppid());
paramMap.put("mchid", wxPayConfig.getMchId());
paramMap.put("description",paymentUser.getDeptName()+"-智慧党建缴费");
paramMap.put("out_trade_no", StringUtils.createOrderNum());
Map<String, Object> amountMap = new HashMap<>();
amountMap.put("total",paymentUser.getTotal()*100);
amountMap.put("currency", "CNY");
paramMap.put("amount",amountMap);

//参数转成json格式
Gson gson = new Gson();
String requestJson = gson.toJson(paramMap);
//将json转成StringEntity对象
StringEntity entity = new StringEntity(requestJson, "utf-8");
entity.setContentType("application/json");
httpPost.setEntity(entity);
httpPost.setHeader("Accept", "application/json");

//发送请求
CloseableHttpClient closeableHttpClient = HttpClients.createDefault();
CloseableHttpResponse response = closeableHttpClient.execute(httpPost);
//4.获取相应结果
String bodyString = EntityUtils.toString(response.getEntity()); //请求后得到的响应体
//状态码
int statusCode = response.getStatusLine().getStatusCode();
//如果处理成功(带响应体的)
if (statusCode == 200) {
   log.info("请求成功 : " + bodyString);
}

//把body中的信息转成map ,直接返回
Map<String, String> resultMap = gson.fromJson(bodyString, HashMap.class);

    return resultMap ;
}