官方建议用app.UseExceptionHandler("/error")来集中处理异常，本例是一个具体的应用。

比如项目中有一个ViewModel，要求Name最大长度为5

/// 
    /// 用户模型    /// 
    public class UserModel    {        /// 
        /// ID        /// 
        public int ID { get; set; }        /// 
        ///名称        /// 
          [MaxLength(5, ErrorMessage = "长度不能超过5")]        public string Name { get; set; }    }

在TestController中有两个Action，都有异常的机率，Get方法中，一个异常是系统内置的0被整除，另一个是我们自定义的业务层级异常(.NET架构小技巧（8）中有涉及);AddUser是有Model验证有可能Name超过5个字符后报异常。Error方法一个错误处理Action，根据上下文的异常来分流系统内置异常，还是自定业务异常。

        /// 
        ///  get接口        /// 
        /// 
            [HttpGet]        public IActionResult Get()        {            var ran = new Random();            switch (ran.Next(1, 4))            {                case 1:                    int i = 0;                    var j = 10 / i;                    return Ok();                case 2:                    throw new RegisteredException("这是一个错误");                default:                    return Ok();            }        }              /// 
        /// 添加用户接口        /// 
        ///         /// 
            [HttpPost("/adduser")]        public IActionResult AddUser([FromBody] UserModel user)        {            return Ok(user);        }        /// 
        /// 错误处理页        /// 
          /// 
            [HttpGet("/error")]        public IActionResult Error()        {            var context = HttpContext.Features.Get
    
     ();            //如果是业务自定义异常，进行特殊处理            if (context.Error is DaMeiException)            {                return Problem(detail: context.Error.StackTrace, title: $"{context.Error.Message}", type: "HIS");            }            else            {                return Problem(detail: context.Error.StackTrace, title: context.Error.Message);            }        }
    

层级异常类

using System;namespace WebApiError{    /// 
    /// 产品异常    /// 
    public class DaMeiException : ApplicationException    {        /// 
        ///         /// 
        ///         public DaMeiException(string message) : base(message)        {        }    }    /// 
    /// His项目异常    /// 
    public class HisException : DaMeiException    {        /// 
        ///         /// 
        ///         public HisException(string message) : base(message)        {        }    }    /// 
    /// Lis项目异常    /// 
    public class LisException : DaMeiException    {        /// 
        ///         /// 
        ///         public LisException(string message) : base(message)        {        }    }    /// 
    /// 模块异常    /// 
    public class RegisteredException : HisException    {        /// 
        ///         /// 
        ///         public RegisteredException(string message) : base(message)        {        }    }}

Error的Action之所有调用到，是因为Configure中添加如下代码，把所有异常交给"/error"来处理。

app.UseExceptionHandler("/error");

添加DaMeiProblemDetailsFactory来兼容各类异常，自定义异常和Model验证异常

using Microsoft.AspNetCore.Http;using Microsoft.AspNetCore.Mvc;using Microsoft.AspNetCore.Mvc.Infrastructure;using Microsoft.AspNetCore.Mvc.ModelBinding;using System.Collections.Generic;namespace WebApiError{    /// 
    ///     /// 
    public class DaMeiProblemDetailsFactory : ProblemDetailsFactory    {        /// 
        /// 处理业务错误        /// 
        ///         ///         ///         ///         ///         ///         /// 
            public override ProblemDetails CreateProblemDetails(HttpContext httpContext, int? statusCode = null, string title = null, string type = null, string detail = null, string instance = null)        {            var problem = new ProblemDetails()            {                Title = string.IsNullOrEmpty(type) ? title : $"业务异常错误：{title}",                Detail = detail,                Status = statusCode,                Instance = instance,                Type = type            };            return problem;        }        /// 
        /// 处理model验证错误        /// 
        ///         ///         ///         ///         ///         ///         ///         /// 
            public override ValidationProblemDetails CreateValidationProblemDetails(HttpContext httpContext, ModelStateDictionary modelStateDictionary, int? statusCode = null, string title = null, string type = null, string detail = null, string instance = null)        {            var problem = new ValidationProblemDetails()            {                Title = "Model验证错误",                Detail = detail,                Status = statusCode,                Instance = instance,                Type = type            };            foreach (var a in modelStateDictionary)            {                var errorList = new List
    
     ();                foreach (var error in a.Value.Errors)                {                    errorList.Add(error.ErrorMessage);                }                problem.Errors.Add(new KeyValuePair
     
      (a.Key, errorList.ToArray()));            }            return problem;        }    }}
     
    

在ConfigureServices中需要注入DaMeiProblemDetailsFactory

services.AddTransient
    
     ();
    

其实还可以用Action过滤器来统一管理异常

using Microsoft.AspNetCore.Mvc;using Microsoft.AspNetCore.Mvc.Filters;namespace WebApiError{    /// 
    /// 自定义过滤器处理异常    /// 
    public class DaMeiExceptionFilter : IActionFilter, IOrderedFilter    {        /// 
        ///         /// 
        public int Order { get; } = int.MaxValue - 10;        /// 
        ///         /// 
        ///         public void OnActionExecuting(ActionExecutingContext context)                {                 }        /// 
        ///         /// 
        ///         public void OnActionExecuted(ActionExecutedContext context)        {            if (context?.Exception != null)            {                context.Result = new ObjectResult(context.Exception.Message)                {                    StatusCode = 500                };                context.ExceptionHandled = true;            }           }    } }

另外一种方式是通过Action过滤器来处理

using Microsoft.AspNetCore.Mvc;using Microsoft.AspNetCore.Mvc.Filters;namespace WebApiError{    /// 
    /// 自定义过滤器处理异常    /// 
    public class DaMeiExceptionFilter : IActionFilter, IOrderedFilter    {        /// 
        ///         /// 
        public int Order { get; } = int.MaxValue - 10;        /// 
        ///         /// 
        ///         public void OnActionExecuting(ActionExecutingContext context)        {        }        /// 
        ///         /// 
        ///         public void OnActionExecuted(ActionExecutedContext context)        {            if (context?.Exception != null)            {                if (context.Exception is DaMeiException)                {                    context.Result = new ObjectResult(context.Exception.Message)                    {                        Value = $"业务异常：{ context.Exception.Message}",                        StatusCode = 500                    };                }                else                {                    context.Result = new ObjectResult(context.Exception.Message)                    {                        Value = context.Exception.Message,                        StatusCode = 500                    };                }                context.ExceptionHandled = true;            }        }    }}

添加全局过滤器

services.AddControllers(options =>{         options.Filters.Add(new DaMeiExceptionFilter());});