ASP.NET Core 3.1--中间件源码解读--RequestDelegate--ApplicationBuilder.Use _application

从来好事天生俭，自古瓜儿苦后甜。这篇文章主要讲述ASP.NET Core 3.1--中间件源码解读--RequestDelegate--ApplicationBuilder.Use相关的知识，希望能为你提供帮助。
一、RequestDelegate的定义
从RequestDelegate定义可以看出，RequestDelegate是接收请求上下文HttpContext的一个委托，RequestDelegate既然是一个委托，委托就是一个方法，所以RequestDelegate就是个方法，是个接受请求上下文的方法。

public delegate Task RequestDelegate(HttpContext context);

二、 IApplicationBuilder.Use的定义
我们对比来看，下面这个func是接收1个int 类型的参数，返回1个string类型的委托

Func< int, string> func = new Func< int, string> (i => { return "abc"; }); string result = func(123);

在看ApplicationBuilder.Use()的定义
ApplicationBuilder.Use方法接收1个Func委托，这个Func接收1个RequestDelegate类型的参数，返回1个RequestDelegate类型，上面说了RequestDelegate是个方法，那么也就是说ApplicationBuilder.Use方法接收1个方法，返回1个方法。

IApplicationBuilder Use(Func< RequestDelegate, RequestDelegate> middleware);

三、ApplicationBuilder.Use需要的参数的简写
这时候requestdelegate是个方法，但是是什么方法，我们还不知道，我们往下看

//1、Func委托，这个Func接收1个RequestDelegate类型的参数，返回1个RequestDelegate类型 Func< RequestDelegate, RequestDelegate> func = new Func< RequestDelegate, RequestDelegate> ((RequestDelegate requestdelegate) => { return new RequestDelegate(async (context) => { await context.Response.WriteAsync("接收1个带RequestDelegate类型的参数，返回RequestDelegate类型的委托"); }); }); //2、简写这个委托 Func< RequestDelegate, RequestDelegate> func = (requestdelegate => { return new RequestDelegate(async (context) => { await context.Response.WriteAsync("简写func委托！"); }); }); //3、Use中间件，最终简写 app.Use(requestdelegate => { return new RequestDelegate(async (context) => { await context.Response.WriteAsync("Use中间件！"); }); });

四、看源码解读中间件注册和执行流程
1、为什么输出顺序是This is Middleware 3=> This is Middleware 2=> This is Middleware 1？ 2、为什么输出顺序是This is Hello World 1 Start=> This is Hello World 2 Start=> This is Hello World 3 Start=> This is Hello World 3 End=> This is Hello World 2 End=> This is Hello World 1 End？

public void Configure(IApplicationBuilder app, IWebHostEnvironment env, ILoggerFactory loggerFactory) { app.Use(next => { Console.WriteLine("This is Middleware 1"); return new RequestDelegate( async context => { await context.Response.WriteAsync("This is Hello World 1 Start"); await next.Invoke(context); await context.Response.WriteAsync("This is Hello World 1 End"); }); }); app.Use(next => { Console.WriteLine("This is Middleware 2"); return new RequestDelegate( async context => { await context.Response.WriteAsync("This is Hello World 2 Start"); await next.Invoke(context); await context.Response.WriteAsync("This is Hello World 2 End"); }); }); app.Use(next => { Console.WriteLine("This is Middleware 3"); return new RequestDelegate( async context => { await context.Response.WriteAsync("This is Hello World 3 Start"); await context.Response.WriteAsync("This is Hello World 3 End"); }); }); }

ASP.NET Core 3.1--中间件源码解读--RequestDelegate--ApplicationBuilder.Use

文章图片

1、ApplicationBuilder.Use方法源码解读
从源码看出ApplicationBuilder.Use方法就是把Func< RequestDelegate, RequestDelegate> middleware添加到_components这个集合里，而从_components的定义看出_components是个委托集合。

文章图片

文章图片

2、中间件执行源码解读
Build()的时候执行注册的中间件从源码看出有个默认的RequestDelegate app，把委托集合反转，遍历执行。第3个中间件的next是默认的RequestDelegate app=> 第2个中间件的next是第3个中间件的返回值=> 第1个中间件的next是第2个中间件的返回值所以先输出This is Middleware 3，后输出This is Middleware 2，最后输出This is Middleware 1，最终返回的是第1个中间件，最终Application就是Middleware 1。所以最后的输出顺序是This is Hello World 1 Start---> This is Hello World 2 Start---> This is Hello World 3 Start---> This is Hello World 3 End---> This is Hello World 2 End---> This is Hello World 1 End