IMiddlewareFactory/IMiddleware 是中间件激活的扩展点。
UseMiddleware 扩展方法检查中间件的已注册类型是否实现 IMiddleware。 如果是,则使用在容器中注册的 IMiddlewareFactory 实例来解析 IMiddleware 实现,而不使用基于约定的中间件激活逻辑。 中间件在应用的服务容器中注册为作用域或瞬态服务。
优点:
- 按客户端请求(作用域服务的注入)激活
- 让中间件强类型化
IMiddleware 按客户端请求(连接)激活,因此作用域服务可以注入到中间件的构造函数中。
IMiddleware
IMiddleware 定义应用的请求管道的中间件。 InvokeAsync(HttpContext, RequestDelegate) 方法处理请求,并返回代表中间件执行的 Task。
使用约定激活的中间件:
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);
}
}
使用 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);
}
}
程序会为中间件创建扩展:
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 将对象传递给工厂激活的中间件:
public static IApplicationBuilder UseFactoryActivatedMiddleware(
this IApplicationBuilder builder, bool option)
{
// Passing 'option' as an argument throws a NotSupportedException at runtime.
return builder.UseMiddleware<FactoryActivatedMiddleware>(option);
}
将工厂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();
}
两个中间件均在 Startup.Configure
的请求处理管道中注册:
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 提供中间件的创建方法。 中间件工厂实现在容器中注册为作用域服务。
可在 Microsoft.AspNetCore.Http 包中找到默认的 IMiddlewareFactory 实现(即 MiddlewareFactory)。