本篇將介紹 ASP.NET Core 的 Middleware，透過 Middleware 掌握封包的進出。
Middleware 運作方式
ASP.NET Core 的每個 Request 都會經過所有註冊的 Middleware，Response 也是逐一回傳，以先進後出的方式處裡封包。
Request 流程如下圖： 
1. 建立 Middleware
Middleware 取代了 ASP.NET MVC 的 HTTP Modules 及 HTTP Handlers，使用方式更為簡潔。
此範例我建立了三個 Middleware，分別在 Request 及 Response 的部分輸出訊息。
如下：
FirstMiddleware.cs
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| public class FirstMiddleware
{
private readonly RequestDelegate _next;
public FirstMiddleware(RequestDelegate next)
{
_next = next;
}
public async Task Invoke(HttpContext context)
{
await context.Response.WriteAsync($"{nameof(FirstMiddleware)} in. \r\n");
await _next(context);
await context.Response.WriteAsync($"{nameof(FirstMiddleware)} out. \r\n");
}
}
|
SecondMiddleware.cs
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| public class SecondMiddleware
{
private readonly RequestDelegate _next;
public SecondMiddleware(RequestDelegate next)
{
_next = next;
}
public async Task Invoke(HttpContext context)
{
await context.Response.WriteAsync($"{nameof(SecondMiddleware)} in. \r\n");
await _next(context);
await context.Response.WriteAsync($"{nameof(SecondMiddleware)} out. \r\n");
}
}
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ThirdMiddleware.cs
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| public class ThirdMiddleware
{
private readonly RequestDelegate _next;
public ThirdMiddleware(RequestDelegate next)
{
_next = next;
}
public async Task Invoke(HttpContext context)
{
await context.Response.WriteAsync($"{nameof(ThirdMiddleware)} in. \r\n");
await _next(context);
await context.Response.WriteAsync($"{nameof(ThirdMiddleware)} out. \r\n");
}
}
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2. 註冊 Middleware
在 Startup.cs 註冊 Middleware：
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| public class Startup
{
public void Configure(IApplicationBuilder app)
{
app.UseMiddleware<FirstMiddleware>();
app.UseMiddleware<SecondMiddleware>();
app.UseMiddleware<ThirdMiddleware>();
app.Run(async (context) =>
{
await context.Response.WriteAsync("Hello World! \r\n");
});
}
}
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執行結果
程式碼下載
asp-net-core-middleware
參考
ASP.NET Core Middleware Fundamentals