下面是关于“.NET Core异常中间件的使用”的完整攻略,包含两个示例说明。
简介
在.NET Core中,异常中间件是一种处理异常的机制。当应用程序抛出未处理的异常时,异常中间件可以捕获该异常并执行一些操作,例如记录异常、发送电子邮件或返回自定义错误页面。本文将详细讲解如何使用.NET Core异常中间件。
使用步骤
使用.NET Core异常中间件的步骤如下:
- 创建一个名为"ExceptionHandlerMiddleware.cs"的文件,并添加以下代码:
using System;
using System.Net;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Logging;
public class ExceptionHandlerMiddleware
{
private readonly RequestDelegate _next;
private readonly ILogger<ExceptionHandlerMiddleware> _logger;
public ExceptionHandlerMiddleware(RequestDelegate next, ILogger<ExceptionHandlerMiddleware> logger)
{
_next = next;
_logger = logger;
}
public async Task Invoke(HttpContext context)
{
try
{
await _next(context);
}
catch (Exception ex)
{
_logger.LogError(ex, "An unhandled exception has occurred.");
await HandleExceptionAsync(context, ex);
}
}
private static Task HandleExceptionAsync(HttpContext context, Exception ex)
{
var code = HttpStatusCode.InternalServerError;
if (ex is UnauthorizedAccessException) code = HttpStatusCode.Unauthorized;
else if (ex is NotFoundException) code = HttpStatusCode.NotFound;
else if (ex is MyException) code = HttpStatusCode.BadRequest;
var result = JsonSerializer.Serialize(new { error = ex.Message });
context.Response.ContentType = "application/json";
context.Response.StatusCode = (int)code;
return context.Response.WriteAsync(result);
}
}
在上面的代码中,我们创建了一个名为"ExceptionHandlerMiddleware"的异常中间件,并实现了"Invoke"方法。在"Invoke"方法中,我们使用try-catch块来捕获未处理的异常,并使用"HandleExceptionAsync"方法来处理异常。在"HandleExceptionAsync"方法中,我们根据异常类型设置HTTP状态码,并返回一个JSON对象,其中包含异常消息。
- 在"Startup.cs"文件中添加以下代码:
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
namespace MvcApp
{
public class Startup
{
public Startup(IConfiguration configuration)
{
Configuration = configuration;
}
public IConfiguration Configuration { get; }
public void ConfigureServices(IServiceCollection services)
{
services.AddControllersWithViews();
}
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
app.UseExceptionHandler(new ExceptionHandlerOptions
{
ExceptionHandler = new ExceptionHandlerMiddleware(env).Invoke
});
app.UseRouting();
app.UseEndpoints(endpoints =>
{
endpoints.MapControllerRoute(
name: "default",
pattern: "{controller=Home}/{action=Index}/{id?}");
});
}
}
}
在上面的代码中,我们在"Configure"方法中使用"UseExceptionHandler"方法来启用异常中间件。
示例
示例1:使用异常中间件记录异常
在本示例中,我们将演示如何使用异常中间件来记录异常。我们可以按照以下步骤来实现:
- 在"ExceptionHandlerMiddleware.cs"文件中添加以下代码:
using System;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Logging;
public class ExceptionHandlerMiddleware
{
private readonly RequestDelegate _next;
private readonly ILogger<ExceptionHandlerMiddleware> _logger;
public ExceptionHandlerMiddleware(RequestDelegate next, ILogger<ExceptionHandlerMiddleware> logger)
{
_next = next;
_logger = logger;
}
public async Task Invoke(HttpContext context)
{
try
{
await _next(context);
}
catch (Exception ex)
{
_logger.LogError(ex, "An unhandled exception has occurred.");
await HandleExceptionAsync(context, ex);
}
}
private static Task HandleExceptionAsync(HttpContext context, Exception ex)
{
context.Response.ContentType = "text/plain";
context.Response.StatusCode = (int)HttpStatusCode.InternalServerError;
return context.Response.WriteAsync("An unexpected error occurred.");
}
}
在上面的代码中,我们在"HandleExceptionAsync"方法中返回一个简单的错误消息,并在"Invoke"方法中使用"ILogger"来记录异常。
- 在"Startup.cs"文件中添加以下代码:
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
namespace MvcApp
{
public class Startup
{
public Startup(IConfiguration configuration)
{
Configuration = configuration;
}
public IConfiguration Configuration { get; }
public void ConfigureServices(IServiceCollection services)
{
services.AddControllersWithViews();
}
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
app.UseExceptionHandler(new ExceptionHandlerOptions
{
ExceptionHandler = new ExceptionHandlerMiddleware(env).Invoke
});
app.UseRouting();
app.UseEndpoints(endpoints =>
{
endpoints.MapControllerRoute(
name: "default",
pattern: "{controller=Home}/{action=Index}/{id?}");
});
}
}
}
在上面的代码中,我们在"Configure"方法中使用"UseExceptionHandler"方法来启用异常中间件。
- 在"HomeController.cs"文件中添加以下代码:
using Microsoft.AspNetCore.Mvc;
public class HomeController : Controller
{
private readonly ILogger<HomeController> _logger;
public HomeController(ILogger<HomeController> logger)
{
_logger = logger;
}
public IActionResult Index()
{
_logger.LogInformation("Index page visited.");
return View();
}
public IActionResult Error()
{
throw new Exception("An unexpected error occurred.");
}
}
在上面的代码中,我们在"Error"方法中抛出一个异常,并在"Index"方法中使用"ILogger"记录日志。
- 在"Index.cshtml"文件中添加以下代码:
@{
ViewBag.Title = "Index";
}
<h2>异常中间件示例</h2>
<a href="/Home/Error">Throw an exception</a>
在上面的代码中,我们创建了一个链接,用户可以点击该链接来触发异常。
- 在命令行中执行以下命令来启动应用程序:
dotnet run
在上面的命令中,我们使用dotnet命令来启动应用程序。
- 在浏览器中打开"http://localhost:5000",然后点击"Throw an exception"链接。在控制台中可以看到异常被记录。
示例2:使用异常中间件返回自定义错误页面
在本示例中,我们将演示如何使用异常中间件来返回自定义错误页面。我们可以按照以下步骤来实现:
- 在"ExceptionHandlerMiddleware.cs"文件中添加以下代码:
using System;
using System.Net;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Abstractions;
using Microsoft.AspNetCore.Mvc.Razor;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.AspNetCore.Mvc.ViewEngines;
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using Microsoft.Extensions.Logging;
public class ExceptionHandlerMiddleware
{
private readonly RequestDelegate _next;
private readonly ILogger<ExceptionHandlerMiddleware> _logger;
private readonly IRazorViewEngine _razorViewEngine;
private readonly ITempDataProvider _tempDataProvider;
public ExceptionHandlerMiddleware(RequestDelegate next, ILogger<ExceptionHandlerMiddleware> logger, IRazorViewEngine razorViewEngine, ITempDataProvider tempDataProvider)
{
_next = next;
_logger = logger;
_razorViewEngine = razorViewEngine;
_tempDataProvider = tempDataProvider;
}
public async Task Invoke(HttpContext context)
{
try
{
await _next(context);
}
catch (Exception ex)
{
_logger.LogError(ex, "An unhandled exception has occurred.");
await HandleExceptionAsync(context, ex);
}
}
private async Task HandleExceptionAsync(HttpContext context, Exception ex)
{
var code = HttpStatusCode.InternalServerError;
if (ex is UnauthorizedAccessException) code = HttpStatusCode.Unauthorized;
else if (ex is NotFoundException) code = HttpStatusCode.NotFound;
else if (ex is MyException) code = HttpStatusCode.BadRequest;
var result = new ViewResult { ViewName = "Error" };
result.StatusCode = (int)code;
result.ViewData = new ViewDataDictionary(new EmptyModelMetadataProvider(), new ModelStateDictionary())
{
{ "Exception", ex }
};
var actionContext = new ActionContext(context, new RouteData(), new ActionDescriptor());
await _razorViewEngine.FindViewAsync(actionContext, result.ViewName, false);
await _tempDataProvider.SaveTempDataAsync(actionContext, result.TempData);
context.Response.ContentType = "text/html";
context.Response.StatusCode = (int)code;
using (var writer = new StreamWriter(context.Response.Body))
{
var viewResult = await _razorViewEngine.RenderViewAsync(actionContext, result.ViewName, false);
await writer.WriteAsync(viewResult);
await writer.FlushAsync();
}
}
}
在上面的代码中,我们在"HandleExceptionAsync"方法中返回一个自定义错误页面,并在"Invoke"方法中使用"IRazorViewEngine"和"ITempDataProvider"来渲染视图和保存临时数据。
- 在"Startup.cs"文件中添加以下代码:
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
namespace MvcApp
{
public class Startup
{
public Startup(IConfiguration configuration)
{
Configuration = configuration;
}
public IConfiguration Configuration { get; }
public void ConfigureServices(IServiceCollection services)
{
services.AddControllersWithViews();
services.AddRazorPages();
}
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
if (env.IsDevelopment())
{
app.UseDeveloperExceptionPage();
}
else
{
app.UseExceptionHandler(new ExceptionHandlerOptions
{
ExceptionHandler = new ExceptionHandlerMiddleware(env).Invoke
});
}
app.UseRouting();
app.UseEndpoints(endpoints =>
{
endpoints.MapControllerRoute(
name: "default",
pattern: "{controller=Home}/{action=Index}/{id?}");
endpoints.MapRazorPages();
});
}
}
}
在上面的代码中,我们在"Configure"方法中使用"UseExceptionHandler"方法来启用异常中间件,并添加了Razor Pages服务。
- 在"Pages"文件夹中创建一个名为"Error.cshtml"的文件,并添加以下代码:
@page
@model ErrorModel
@{
ViewData["Title"] = "Error";
}
<h1 class="text-danger">Error</h1>
<p>An unexpected error has occurred:</p>
<pre>@Model.Exception</pre>
在上面的代码中,我们创建了一个名为"Error"的Razor页面,用于显示异常消息。
- 在"HomeController.cs"文件中添加以下代码:
using Microsoft.AspNetCore.Mvc;
public class HomeController : Controller
{
public IActionResult Index()
{
return View();
}
public IActionResult Error()
{
throw new Exception("An unexpected error occurred.");
}
}
在上面的代码中,我们在"Error"方法中抛出一个异常。
- 在"Index.cshtml"文件中添加以下代码:
@{
ViewBag.Title = "Index";
}
<h2>异常中间件示例</h2>
<a href="/Home/Error">Throw an exception</a>
在上面的代码中,我们创建了一个链接,用户可以点击该链接来触发异常。
- 在命令行中执行以下命令来启动应用程序:
dotnet run
在上面的命令中,我们使用dotnet命令来启动应用程序。
- 在浏览器中打开"http://localhost:5000",然后点击"Throw an exception"链接。在页面中可以看到自定义错误页面,并显示异常消息。
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