假设我们有一个MES系统，它提供了一个RESTful API用于获取订单信息。API的URL是https://api.mes-system.com/orders/{orderId}，其中{orderId}是一个占位符，需要替换为实际的订单ID。
以下是demo：

using System;  
using System.Net.Http;  
using System.Text;  
using System.Threading.Tasks;  
using Newtonsoft.Json; // 引入Json.NET库来处理JSON  public class MesApiClient  
{  private readonly HttpClient _httpClient;  private readonly string _baseUrl = "https://api.mes-system.com/orders/";  public MesApiClient()  {  // 初始化HttpClient，这里可以根据需要配置HttpClientHandler等  _httpClient = new HttpClient();  }  public async Task<Order> GetOrderAsync(string orderId)  {  if (string.IsNullOrEmpty(orderId))  {  throw new ArgumentException("Order ID is required", nameof(orderId));  }  // 构建完整的URL  var url = _baseUrl + orderId;  // 发送GET请求  HttpResponseMessage response = await _httpClient.GetAsync(url);  // 确保请求成功  response.EnsureSuccessStatusCode();  // 读取响应内容  string responseBody = await response.Content.ReadAsStringAsync();  // 将JSON响应反序列化为Order对象  Order order = JsonConvert.DeserializeObject<Order>(responseBody);  // 返回Order对象  return order;  }  
}  // 假设的Order类，用于反序列化JSON响应  
public class Order  
{  public string OrderId { get; set; }  public string CustomerName { get; set; }  public DateTime OrderDate { get; set; }  // 其他属性...  
}  // 使用示例  
class Program  
{  static async Task Main(string[] args)  {  // 创建MES API客户端实例  var mesApiClient = new MesApiClient();  // 假设的订单ID  string orderId = "12345";  try  {  // 调用GetOrderAsync方法来获取订单信息  Order order = await mesApiClient.GetOrderAsync(orderId);  // 输出订单信息  Console.WriteLine($"Order ID: {order.OrderId}, Customer: {order.CustomerName}, Order Date: {order.OrderDate}");  }  catch (Exception ex)  {  // 处理异常  Console.WriteLine("An error occurred: " + ex.Message);  }  }  
}