:::info

1. 切面编程机制，在ASP.NET Core特定的位置执行我们自定义的代码。
2. ASP.NET Core中的Filter的五种类型:Authorization Filter、Resource filter、Action filter、Exception filter、Result filter
3. 所有筛选器一般有同步和异步两个版本，比如IActionFilter、IAsyncActionFilter接口.
4. OnAuthorization→OnResourceExecuting→创建控制器→OnActionExecuting→执行action业务→OnActionExecuted→OnResultExecuting→页面渲染加载→OnResultExecuted→OnResourceExecuted

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Exception

:::info

1. 当系统中出现未处理异常的 时候,我们需要统一给客户返回一个友好的讯息：{“code”:”500”,”message”:”异常信息”}

:::

using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Filters;
namespace Filter1
{
    //添加Attribute 是为了可以在当成特性添加到control或者Action上
    public class MyExceptionFilter : Attribute, IAsyncExceptionFilter
    {
        public Task OnExceptionAsync(ExceptionContext context)
        {
            // context.Exception代表异常信息对象
            //如果context.ExceptionHandled=true ,则其他 ExceptionFilter不会再执行
            // context.Result 的值会被输出到客户端
            string msg;
            msg = context.Exception.Message; 
            ObjectResult result = new ObjectResult(new { code = 500, message = msg });
            context.Result = result;
            context.ExceptionHandled = true; // 表示当前异常被处理过
            Console.WriteLine("进入了异常");
            return Task.CompletedTask;
        }
    }
}
//全局注册使用
using Microsoft.AspNetCore.Mvc;
builder.Services.Configure<MvcOptions>(option =>
{
    option.Filters.Add<MyExceptionFilter>();
});

Action Filter

IActionFilter同步

定义Filter

public class CustomerActionFilterAttribute : Attribute, IActionFilter
    {
        /// <summary>
        /// 在XXAction执行之前
        /// </summary>
        /// <param name="context"></param>
        public void OnActionExecuting(ActionExecutingContext context)
        {
            Console.WriteLine("CustomerActionFilterAttribute.OnActionExecuting");
        }
        /// <summary>
        /// 在XXAction执行之后
        /// </summary>
        /// <param name="context"></param>
        public void OnActionExecuted(ActionExecutedContext context)
        {
            Console.WriteLine("CustomerActionFilterAttribute.OnActionExecuted");
        }    
    }

使用Filter

//1. 全局注册Program.cs
builder.Services.Configure<MvcOptions>(option =>
{
    option.Filters.Add<MyExceptionFilter>();   
    option.Filters.Add<CustomerActionFilterAttribute>();
});
//2.controller类或者Action方法注册
public class Home1Controller : Controller
    {
        private readonly ILogger<HomeController> _logger;
        public Home1Controller(ILogger<HomeController> logger)
        {
            _logger = logger;
            Console.WriteLine($"执行 {this.GetType().Name} 构造函数");
        }
        [CustomerActionFilter]
        public IActionResult Index()
        {
            Console.WriteLine($"执行 Index 方法");
            return View();
        }
    }

扩展记录日志

  public class CustomerActionFilterAttribute : Attribute, IActionFilter
    {
        private readonly ILogger<CustomerActionFilterAttribute> _logger;
        public CustomerActionFilterAttribute(ILogger<CustomerActionFilterAttribute> _logger)
        {
            this._logger = _logger;
            Gid = Guid.NewGuid().ToString();
        }
        private string Gid; //用于测试他们执行一个Action是不是同一个对象
        public void OnActionExecuting(ActionExecutingContext context)
        {
            string ExecuteParam = "";
            string Executeurl = context.HttpContext.Request.Path;
            switch (context.HttpContext.Request.Method.ToUpper())
            {
                case "GET":
                    ExecuteParam = context.HttpContext.Request.QueryString.Value.ToString();
                    break;
                case "POST":
                    Executeurl += context.HttpContext.Request.QueryString.Value.ToString();
                    ExecuteParam = JsonConvert.SerializeObject(context.ActionArguments);
                    break;
                default:
                    break;
            }
            var controllerName = context.ActionDescriptor.RouteValues["controller"];
            var actionName = context.ActionDescriptor.RouteValues["action"];
            _logger.LogInformation($"当前请求的Url是{Executeurl},控制器是{controllerName},方法名{actionName},请求参数是{ExecuteParam}，guid={Gid}");
        }
        public void OnActionExecuted(ActionExecutedContext context)
        {
            var para = (context.Result as ObjectResult).Value;
            var controllerName = context.ActionDescriptor.RouteValues["controller"];
            var actionName = context.ActionDescriptor.RouteValues["action"];
            _logger.LogInformation($"当前请求的控制器是{controllerName},方法名{actionName},请求结果是{JsonConvert.SerializeObject(para)},guid={Gid}");
        }

使用 扩展记录日志

// 1.全局注册
builder.Services.Configure<MvcOptions>(option =>
{
    option.Filters.Add<MyExceptionFilter>();  
    option.Filters.Add<CustomerActionFilterAttribute>();
});
//2.controller类或者Action方法注册
  [TypeFilter(typeof(CustomerActionFilterAttribute))]

IAsyncActionFilter（异步）

定义Filter

public class CustomerAsyncActionFilterAttribute : Attribute, IAsyncActionFilter
    {
        private readonly ILogger<CustomerAsyncActionFilterAttribute> _logger;
        public CustomerAsyncActionFilterAttribute(ILogger<CustomerAsyncActionFilterAttribute> logger)
        {
            _logger = logger;
        }
        public async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)
        {
            var para = context.HttpContext.Request.QueryString.Value;
            var controllerName = context.ActionDescriptor.RouteValues["controller"];
            var actionName = context.ActionDescriptor.RouteValues["action"];
            _logger.LogInformation($"当前请求的控制器是{controllerName},方法名{actionName},请求参数是{JsonConvert.SerializeObject(para)}");
            var excuteContext = await next.Invoke(); // 这句话就是去执行Action
            _logger.LogInformation($"当前请求的控制器是{controllerName},方法名{actionName},请求结果是{JsonConvert.SerializeObject(excuteContext.Result)}");
        }
    }

使用Filter

public class Home1Controller : Controller
    {
        private readonly ILogger<HomeController> _logger;
        public Home1Controller(ILogger<HomeController> logger)
        {
            _logger = logger;
            Console.WriteLine($"执行 {this.GetType().Name} 构造函数");
        }
        //[TypeFilter(typeof(CustomerActionFilterAttribute))]
        [TypeFilter(typeof(CustomerAsyncActionFilterAttribute))] //注册
        public IActionResult Index(int id)
        {
            Console.WriteLine($"执行 Index 方法");
            ViewBag.Data = new { name = "11111" };
            return View();
        }
    }
//全局注册Program.cs 也可以
builder.Services.Configure<MvcOptions>(option =>
{
    option.Filters.Add<MyExceptionFilter>();   
    option.Filters.Add<CustomerAsyncActionFilterAttribute>();
});

执行顺序

:::info

4、执行CustomerActionFilterAttribute.OnActionExecuted

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案例：对请求限速的ActionFilter

using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Filters;
using Microsoft.Extensions.Caching.Memory;
namespace Filter1
{
    public class RateLimitActionFilter : Attribute, IAsyncActionFilter
    {
        private readonly IMemoryCache memoryCache;
        public RateLimitActionFilter(IMemoryCache memoryCache)
        {
            this.memoryCache = memoryCache;
        }
        public async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)
        {
            string ip = context.HttpContext.Connection.RemoteIpAddress.ToString();
            string cacheKey = $"lastvisittick_{ip}";
            long? lastVisit = memoryCache.Get<long>(cacheKey);
            if (lastVisit == null || Environment.TickCount64 - lastVisit > 1000)
            {
                memoryCache.Set(cacheKey, Environment.TickCount64, TimeSpan.FromSeconds(10));
                await next();
            }
            else
            {
                ObjectResult objectResult = new ObjectResult("访问太频繁") { StatusCode = 429 };
                context.Result = objectResult;
            }
        }
    }
}
//注入使用
builder.Services.AddMemoryCache(); //添加ImemoryCache
builder.Services.Configure<MvcOptions>(option =>
{
    option.Filters.Add<RateLimitActionFilter>();  //全局注入
    option.Filters.Add<MyExceptionFilter>();  
    option.Filters.Add<CustomerActionFilterAttribute>();
});
//也可以通过特性的方式单独添加到Action/controller上
   [TypeFilter(typeof(RateLimitActionFilter))]