ASP.NET Core中显示自定义错误页面-增强版

之前的博文 ASP.NET Core中显示自定义错误页面 中的方法是在项目中硬编码实现的，当有多个项目时，就会造成不同项目之间的重复代码，不可取。

在这篇博文中改用middleware实现，并且放在独立的项目中发布成NuGet包，项目中使用时只需安装NuGet包，然后在Startup的Configure()方法中添加如下的一行代码。

app.UseCustomErrorPages();

CustomErrorPagesMiddleware的实现代码如下：

public class CustomErrorPagesMiddleware
{
    private readonly RequestDelegate _next;
    private readonly ILogger _logger;

    public CustomErrorPagesMiddleware(
        RequestDelegate next,
        ILoggerFactory loggerFactory)
    {
        _next = next;
        _logger = loggerFactory.CreateLogger<CustomErrorPagesMiddleware>();
    }

    public async Task Invoke(HttpContext context)
    {
        try
        {
            await _next(context);
        }
        catch (Exception ex)
        {
            _logger.LogError(, ex, "An unhandled exception has occurred while executing the request");

            if (context.Response.HasStarted)
            {
                _logger.LogWarning("The response has already started, the error page middleware will not be executed.");
                throw;
            }
            try
            {
                context.Response.Clear();
                context.Response.StatusCode = ;
                return;
            }
            catch (Exception ex2)
            {
                _logger.LogError(, ex2, "An exception was thrown attempting to display the error page.");
            }
            throw;
        }
        finally
        {
            var statusCode = context.Response.StatusCode;
            if (statusCode ==  || statusCode == )
            {
                await ErrorPage.ResponseAsync(context.Response, statusCode);
            }
        }
    }
}

ErrorPage的实现代码如下：

public static class ErrorPage
{
    public static async Task ResponseAsync(HttpResponse response, int statusCode)
    {
        if (statusCode == )
        {
            await response.WriteAsync(Page404);
        }
        else if (statusCode == )
        {
            await response.WriteAsync(Page500);
        }
    }

    private static string Page404 => @"html...";

    private static string Page500 => @"html...";
}

CustomErrorPagesExtensions的实现代码如下：

public static class CustomErrorPagesExtensions
{
    public static IApplicationBuilder UseCustomErrorPages(this IApplicationBuilder app)
    {
        if (app == null)
        {
            throw new ArgumentNullException(nameof(app));
        }

        return app.UseMiddleware<CustomErrorPagesMiddleware>();
    }
}

代码参考自：

1）CustomErrorPagesMiddleware.cs

2）DeveloperExceptionPageMiddleware.cs