如何在 .NET Core中获取HttpContext？

什么是HttpContext？

它保存有关Http请求的当前信息，包含诸如授权、身份验证、请求、响应、会话、项目、用户、formOptions等信息。每个HTTP请求都会使用当前信息创建HttpContext的新对象。

关于 HttpContext

• 在 ASP.NET 的时代，我们通常通过 HttpContext 全局静态类获取请求上下文，
• 在 ASP.NET Core 中，HttpContext 是一个非静态的抽象类，无法手动创建，也无法通过静态获取。
  • ControllerBase 派生类中使用
  • 微软也提供了注入 IHttpContextAccessor 方式获取
     

 1、获取 HttpContext（在 ControllerBase 派生类中）

        [HttpGet]
        public string Get1()
        {
            var ip = HttpContext.Connection.RemoteIpAddress.ToString();
            return ip; 
        }

2、获取 HttpContext（注入 IHttpContextAccessor）

• 在 Startup.cs 中注册服务

  services.AddHttpContextAccessor();//注册 HttpContextAccessor 服务

• 构造函数注入 或 参数注入方式 [FromServices]

          private readonly IHttpContextAccessor _httpContextAccessor;
          //构造函数注入
          public HttpContextController(IHttpContextAccessor httpContextAccessor)
          {
              _httpContextAccessor = httpContextAccessor;
          }

          //参数注入方式 [FromServices]
          [HttpGet]
          public string Get4([FromServices] IHttpContextAccessor httpContextAccessor)
          {
              var ip = httpContextAccessor.HttpContext.Connection.RemoteIpAddress.ToString();
              return ip; 
          }

   

3、获取 HttpContext（注入 IHttpContextAccessor+AppHttpContext.css静态类）

• AppHttpContext.css 公共静态类

      public static class AppHttpContext
      {
          private static IHttpContextAccessor _httpContextAccessor;
  
          public static void Configure(IHttpContextAccessor httpContextAccessor)
          {
              _httpContextAccessor = httpContextAccessor;
          } 
          public static HttpContext HttpContext
          {
              get
              {
                  if (_httpContextAccessor == null)
                  {
                      throw new InvalidOperationException("尚未配置IHttpContextAccessor");
                  } 
                  return _httpContextAccessor.HttpContext;
              }
          } 
      }

• Startup.cs

          public void ConfigureServices(IServiceCollection services)
          {
              services.AddHttpContextAccessor();//注册 HttpContextAccessor 服务，源码为：services.TryAddSingleton<IHttpContextAccessor, HttpContextAccessor>();
          }
  
          public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
          { 
              var httpContextAccessor = app.ApplicationServices.GetRequiredService<IHttpContextAccessor>();
              AppHttpContext.Configure(httpContextAccessor);
          }

•         //AppHttpContext 静态类也提供了 AppHttpContext.HttpContext 获取 HttpContext 对象。
          [HttpGet]
          public string Get2()
          {
              var ip = AppHttpContext.HttpContext.Connection.RemoteIpAddress.ToString();
              return ip;
          }

  避免在多线程，事件总线，定时任务等中使用。(线程安全问题等)