详解ASP.NET Core 中基于工场的中间件激活的实现要领

IMiddlewareFactory/IMiddleware是中间件激活的扩展点。

UseMiddleware扩展要领搜查中间件的已注册范例是否实现IMiddleware。假如是，则行使在容器中注册的IMiddlewareFactory实例来理会IMiddleware实现，而不行使基于约定的中间件激活逻辑。中间件在应用的处事容器中注册为浸染域或瞬态处事。

利益：

按客户端哀求（浸染域处事的注入）激活

让中间件强范例化

IMiddleware按客户端哀求（毗连）激活，因此浸染域处事可以注入到中间件的结构函数中。

IMiddleware

IMiddleware界说应用的哀求管道的中间件。InvokeAsync(HttpContext, RequestDelegate)要领处理赏罚哀求，并返回代表中间件执行的Task。

行使约定激活的中间件：

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); } }

行使MiddlewareFactory激活的中间件：

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); } }

措施会为中间件建设扩展：

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>(); } }

无法通过UseMiddleware将工具转达给工场激活的中间件：

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

将工场激活的中间件添加到Startup.ConfigureServices的内置容器中：

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

两此中间件均在Startup.Configure的哀求处理赏罚管道中注册：

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(); }); }

IMiddlewareFactory

IMiddlewareFactory提供中间件的建设要领。中间件工场实此刻容器中注册为浸染域处事。

可在Microsoft.AspNetCore.Http包中找到默认的IMiddlewareFactory实现（即MiddlewareFactory）。

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