详解ASP.NET Core 中基于工厂的中间件激活的实现方

public class ConventionalMiddleware
{
 private readonly RequestDelegate _next;

 public ConventionalMiddleware(RequestDelegate next)
 {
  _next = next;
 }

 public async Task InvokeAsync(HttpContext context, AppDbContext db)
 {
  var keyValue = context.Request.Query["key"];

  if (!string.IsNullOrWhiteSpace(keyValue))
  {
   db.Add(new Request()
    {
     DT = DateTime.UtcNow, 
     MiddlewareActivation = "ConventionalMiddleware", 
     Value = keyValue
    });

   await db.SaveChangesAsync();
  }

  await _next(context);
 }
}

public class FactoryActivatedMiddleware : IMiddleware
{
 private readonly AppDbContext _db;

 public FactoryActivatedMiddleware(AppDbContext db)
 {
  _db = db;
 }

 public async Task InvokeAsync(HttpContext context, RequestDelegate next)
 {
  var keyValue = context.Request.Query["key"];

  if (!string.IsNullOrWhiteSpace(keyValue))
  {
   _db.Add(new Request()
    {
     DT = DateTime.UtcNow, 
     MiddlewareActivation = "FactoryActivatedMiddleware", 
     Value = keyValue
    });

   await _db.SaveChangesAsync();
  }

  await next(context);
 }
}

public static class MiddlewareExtensions
{
 public static IApplicationBuilder UseConventionalMiddleware(
  this IApplicationBuilder builder)
 {
  return builder.UseMiddleware<ConventionalMiddleware>();
 }

 public static IApplicationBuilder UseFactoryActivatedMiddleware(
  this IApplicationBuilder builder)
 {
  return builder.UseMiddleware<FactoryActivatedMiddleware>();
 }
}

public static IApplicationBuilder UseFactoryActivatedMiddleware(
 this IApplicationBuilder builder, bool option)
{
 // Passing 'option' as an argument throws a NotSupportedException at runtime.
 return builder.UseMiddleware<FactoryActivatedMiddleware>(option);
}

public void ConfigureServices(IServiceCollection services)
{
 services.AddDbContext<AppDbContext>(options =>
  options.UseInMemoryDatabase("InMemoryDb"));

 services.AddTransient<FactoryActivatedMiddleware>();

 services.AddRazorPages();
}

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
 if (env.IsDevelopment())
 {
  app.UseDeveloperExceptionPage();
 }
 else
 {
  app.UseExceptionHandler("/Error");
 }

 app.UseConventionalMiddleware();
 app.UseFactoryActivatedMiddleware();

 app.UseStaticFiles();
 app.UseRouting();

 app.UseEndpoints(endpoints =>
 {
  endpoints.MapRazorPages();
 });
}