5 .net core 基于工厂的中间件激活

基于工厂的中间件需要继承IMiddleware接口，在请求到来时，会从IMiddlewareFactory中获取中间件实例
如果中间件没有继承IMiddleware接口，则不会从IMiddlewareFactory中获取
.netcore具有IMiddlewareFactory的默认实现

IMiddleware

使用基于工厂的中间件（继承IMiddleware接口）：

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);
    }
}

为中间件创建扩展

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

将工厂中间件添加内置容器中

public void ConfigureServices(IServiceCollection services)
{
    ...
    services.AddTransient<FactoryActivatedMiddleware>();
}

应用中间件

public void Configure (IApplicationBuilder app, IHostingEnvironment env) {
    ...
    app.UseConventionalMiddleware ();
    ...

IMiddlewareFactory

IMiddlewareFactory 作为域服务注册在容器中