ASP.NET Core Middleware 的调用顺序
ASP.NET Core 请求管道包含一系列请求委托，依次调用。而调用顺序实际上就是我们在 Startup.cs 中注册（使用 UseMiddlewareExtensions.UseMiddleware 方法）它们的顺序。
示例代码如下：
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public void ConfigureServices(IServiceCollection services)
{
//注册生命周期
services.AddTransient<TransientMiddleware>();
services.AddScoped<ScopedMiddleware>();
}
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
//注册调用顺序
app.UseMiddleware<TransientMiddleware>();
app.UseMiddleware<ScopedMiddleware>();
}
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但这种方式，对于调整自定义 Middleware 的需求，需要经常修改 Startup.cs，而且会使代码比较凌乱，可读性较差。
可以使用下面的方式，简化注册代码：
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public void ConfigureServices(IServiceCollection services)
{
services.AddMiddlewares();
}
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
app.UseMiddlewares();
}
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实现方式
1. 定义 Attribute
MiddlewareRegisterAttribute 将放在每个 Middleware 实现类上，表明它是需要被注册的 Middleware。
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[AttributeUsage(AttributeTargets.Class)]
public class MiddlewareRegisterAttribute : Attribute
{
// 注册顺序
public int Sort { get; set; } = int.MaxValue;
// 生命周期
public ServiceLifetime Lifetime { get; set; } = ServiceLifetime.Scoped;
}
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2. 定义注册信息类
MiddlewareRegisterInfo 用于存放 Middleware 的注册信息，供注册方法调用。
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public class MiddlewareRegisterInfo
{
public MiddlewareRegisterInfo(Type type,MiddlewareRegisterAttribute attribute)
{
Type = type;
Sort = attribute.Sort;
Lifetime = attribute.Lifetime;
}
public Type Type { get; private set; }
public int Sort { get; private set; }
public ServiceLifetime Lifetime { get; private set; }
}
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3. 实现注册扩展方法
读取 Assembly 中的 Type, 如果存在 MiddlewareRegisterAttribute 就把它放入 List<MiddlewareRegisterInfo> 列表中，最后根据 Sort 属性顺序依次注册，代码如下：
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public static class MiddlewareRegisterExtensions
{
private static readonly IEnumerable<MiddlewareRegisterInfo> _middlewareRegisterInfos = GetMiddlewareRegisterInfos();
public static IServiceCollection AddMiddlewares(this IServiceCollection services)
{
foreach (var middlewareRegisterInfo in _middlewareRegisterInfos)
{
switch (middlewareRegisterInfo.Lifetime)
{
case ServiceLifetime.Singleton:
services.AddSingleton(middlewareRegisterInfo.Type);
break;
case ServiceLifetime.Transient:
services.AddTransient(middlewareRegisterInfo.Type);
break;
default:
services.AddScoped(middlewareRegisterInfo.Type);
break;
}
}
return services;
}
public static IApplicationBuilder UseMiddlewares(this IApplicationBuilder applicationBuilder)
{
foreach (var middlewareRegisterInfo in _middlewareRegisterInfos)
{
applicationBuilder.UseMiddleware(middlewareRegisterInfo.Type);
}
return applicationBuilder;
}
private static List<MiddlewareRegisterInfo> GetMiddlewareRegisterInfos()
{
var middlewareRegisterInfos = new List<MiddlewareRegisterInfo>();
//所有包含Middleware的Assembly
var assemblies = new Assembly[] { typeof(Startup).Assembly };
foreach (var assembly in assemblies)
{
foreach (var type in assembly.GetTypes().Where(x => !x.IsAbstract))
{
var attribute = type.GetCustomAttribute<MiddlewareRegisterAttribute>();
if (attribute != null)
{
middlewareRegisterInfos.Add(new MiddlewareRegisterInfo(type, attribute));
}
}
}
return middlewareRegisterInfos.OrderBy(p=>p.Sort).ToList();
}
}
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测试一下
创建 3 个 Middleware，功能仅仅是输出日志：
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[MiddlewareRegister(Sort = 100)]
public class OneMiddleware : IMiddleware
{
private readonly ILogger<OneMiddleware> logger;
public OneMiddleware(ILogger<OneMiddleware> logger)
{
this.logger = logger;
}
public async Task InvokeAsync(HttpContext context, RequestDelegate next)
{
logger.LogInformation("One");
await next(context);
}
}
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Sort 用 100、200、300，方便后面修改排序。
运行效果如下图：
现在，将 ThreeMiddleware 的 Sort 改为 150，调整注册顺序，再次运行，效果如下图：
结论
当然，这个解决方案也存在一些缺点，比如修改排序的位置移到每个 Middleware，比较分散。但整体来说，代码更易读！
反骨仔