ApplicationBuilder(IApplicationBuilder接口)，是OWIN的基础，而且里面都是代理、代理的代理，各种lambda表达式，估计要看这部分代码，很多人得头昏脑涨。今天就对个类以及几个扩展方法进行讲解。
按惯例先贴代码（这是我修改后的，将接口继承去掉了、HttpContext类修改成自己的MyHttpContext类）
public class ApplicationBuilder { private readonly IList<Func<RequestDelegate, RequestDelegate>> _components = new List<Func<RequestDelegate, RequestDelegate>>(); public ApplicationBuilder() { } private ApplicationBuilder(ApplicationBuilder builder) { } public ApplicationBuilder Use(Func<RequestDelegate, RequestDelegate> middleware) { _components.Add(middleware); return this; } public ApplicationBuilder New() { return new ApplicationBuilder(this); } public RequestDelegate Build() { RequestDelegate app = context => { context.StatusCode = "404"; System.Console.WriteLine("404"); return Task.FromResult(0); }; foreach (var component in _components.Reverse()) { app = component(app); } return app; } }RequestDelegate的定义如下：
public delegate Task RequestDelegate(MyHttpContext context);
从ApplicationBuilder的源代码中我们可以关注3个点：_components、Use方法、Build方法。
_components是也一个列表（IList）对象，不过里面类型有点特殊——是以代理RequestDelegate为参数、代理RequestDelegate为返回值的一个代理。这里用代理说有点别嘴，可以把代理叫做函数，就是里面的类型是一个函数，这个函数的参数也是函数，返回值也是函数。Use方法，就是在上面的列表对象后面添加一条新记录。Build方法就是将_components数组按照反向顺序，制作成一个链式结构（有点类似链表的感觉）。下面用俩幅图说明下：Build之前
{ throw new ArgumentNullException("How?"); } app.Use(_ => handler); } }
首先说Use方法，改方法是对之前Use方法的一个更改。将传入的参数更改为Func<MyHttpContext, Func<Task>, Task>。这样做有什么好处？之前的Func<RequestDelegate, RequestDelegate>对象并不能给人清楚的明了的感觉，而Func<MyHttpContext, Func<Task>, Task>就非常明确了。传入的参数：MyHttpContext就是Context对象，Func<Task>就是next的执行体。返回值是一个Task（类似于void）。一目了然。
再说Run方法，显而易见，Run方法只执行自己的内容，并没有执行参数体。所以链式结构的在其前的都会被舍弃，不会被执行。
最后把自己的测试例子贴出来，供大家参考
示例1：
static void Main(string[] args) { MyHttpContext context = new MyHttpContext() { StatusCode = "A" }; Func<MyHttpContext, Func<Task>, Task> middleware = (x, y) => { context.StatusCode += "C"; System.Console.WriteLine(context.StatusCode); return y(); }; Func<MyHttpContext, Func<Task>, Task> middleware2 = (x, y) => { context.StatusCode += "End1"; System.Console.WriteLine(context.StatusCode); return Task.FromResult(0); }; ApplicationBuilder builder = new ApplicationBuilder(); builder.Use( next => { return (MyHttpContext o) => { o.StatusCode += "B"; System.Console.WriteLine(context.StatusCode); next(o); return Task.FromResult(0); }; } ); builder.Use(middleware); //builder.Use(middleware2); //builder.Use(middleware); //builder.Run(o => { o.StatusCode += "End2"; return Task.FromResult(0); }); builder.Build().Invoke(context); System.Console.ReadLine(); }执行结果：
示例2：
static void Main(string[] args) { MyHttpContext context = new MyHttpContext() { StatusCode = "A" }; Func<MyHttpContext, Func<Task>, Task> middleware = (x, y) => { context.StatusCode += "C"; System.Console.WriteLine(context.StatusCode); return y(); }; Func<MyHttpContext, Func<Task>, Task> middleware2 = (x, y) => { context.StatusCode += "End1"; System.Console.WriteLine(context.StatusCode); return Task.FromResult(0); }; ApplicationBuilder builder = new ApplicationBuilder(); builder.Use( next => { return (MyHttpContext o) => { o.StatusCode += "B"; System.Console.WriteLine(context.StatusCode); next(o); return Task.FromResult(0); }; } ); builder.Use(middleware); builder.Use(middleware2); //builder.Use(middleware); //builder.Run(o => { o.StatusCode += "End2"; System.Console.WriteLine(context.StatusCode); return Task.FromResult(0); }); builder.Build().Invoke(context); System.Console.ReadLine(); }执行结果：
示例3：
static void Main(string[] args) { MyHttpContext context = new MyHttpContext() { StatusCode = "A" }; Func<MyHttpContext, Func<Task>, Task> middleware = (x, y) => { context.StatusCode += "C"; System.Console.WriteLine(context.StatusCode); return y(); }; Func<MyHttpContext, Func<Task>, Task> middleware2 = (x, y) => { context.StatusCode += "End1"; System.Console.WriteLine(context.StatusCode); return Task.FromResult(0); }; ApplicationBuilder builder = new ApplicationBuilder(); builder.Use( next => { return (MyHttpContext o) => { o.StatusCode += "B"; System.Console.WriteLine(context.StatusCode); next(o); return Task.FromResult(0); }; } ); builder.Use(middleware); //builder.Use(middleware2); //builder.Use(middleware); builder.Run(o => { o.StatusCode += "End2"; System.Console.WriteLine(context.Statwww.easck.comusCode); return Task.FromResult(0); }); builder.Build().Invoke(context); System.Console.ReadLine(); }执行结果：
到此这篇关于详解Asp.net 5中的ApplicationBuilder的文章就介绍到这了。希望对大家的学习有所帮助，也希望大家多多支持我们。
