ASP.NET Core中顯示自定義錯誤頁面-增強版

之前的博文 ASP.NET Core中顯示自定義錯誤頁面 中的方法是在項目中硬編碼實現的，當有多個項目時，就會造成不同項目之間的重復代碼，不可取。

在這篇博文中改用middleware實現，並且放在獨立的項目中發布成NuGet包，項目中使用時只需安裝NuGet包，然后在Startup的Configure()方法中添加如下的一行代碼。

app.UseCustomErrorPages();

CustomErrorPagesMiddleware的實現代碼如下：

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(0, 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 = 500;
                return;
            }
            catch (Exception ex2)
            {
                _logger.LogError(0, ex2, "An exception was thrown attempting to display the error page.");
            }
            throw;
        }
        finally
        {
            var statusCode = context.Response.StatusCode;
            if (statusCode == 404 || statusCode == 500)
            {
                await ErrorPage.ResponseAsync(context.Response, statusCode);
            }
        }
    }
}

ErrorPage的實現代碼如下：

public static class ErrorPage
{
    public static async Task ResponseAsync(HttpResponse response, int statusCode)
    {
        if (statusCode == 404)
        {
            await response.WriteAsync(Page404);
        }
        else if (statusCode == 500)
        {
            await response.WriteAsync(Page500);
        }
    }

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

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

CustomErrorPagesExtensions的實現代碼如下：

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

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

代碼參考自：

1）CustomErrorPagesMiddleware.cs

2）DeveloperExceptionPageMiddleware.cs