摘要：
1. 概述 “）；}）；｝｝第一个Run委托终止了管道。Use用于将多个请求委托链接在一起。下一个参数表示管道中的下一个委托。您可以通过不调用下一参数来短路管道。publicvoid配置｛app.Use；app.Run（asyncontext=˃｛awaicontext.Response.WriteAsync（“输入第二个委托”）; 等待上下文。回答WriteAsync（“HelloWorld！”！
ASP.NET Core中的中间件是嵌入到应用管道中用于处理请求和响应的一段代码。
2.使用 IApplicationBuilder 创建中间件管道2.1 匿名函数
使用Run, Map, Use ,MapWhen等扩展方法来实现。
usingMicrosoft.AspNetCore.Builder; usingMicrosoft.AspNetCore.Hosting; usingMicrosoft.AspNetCore.Http; public classStartup { public voidConfigure(IApplicationBuilder app) { app.Run(async context => { await context.Response.WriteAsync("Hello World!"); }); } }
第一个Run委托终止了管道。
用 Use 将多个请求委托链接在一起。 next 参数表示管道中的下一个委托。 可通过不 调用 next 参数使管道短路。
public voidConfigure(IApplicationBuilder app, IHostingEnvironment env) { app.Use(async (context, next) => { context.Response.ContentType = "text/plain;charset=utf-8"; await context.Response.WriteAsync("进入第一个委托 执行下一个委托之前 "); //调用管道中的下一个委托 awaitnext.Invoke(); await context.Response.WriteAsync("结束第一个委托 执行下一个委托之后 "); }); app.Run(async context => { await context.Response.WriteAsync("进入第二个委托 "); await context.Response.WriteAsync("Hello World! "); await context.Response.WriteAsync("结束第二个委托 "); }); }
2.2 自定义中间件类
新建中间件类：MyMiddleware.cs
usingMicrosoft.AspNetCore.Http; public classMyMiddleware { private readonlyRequestDelegate _next; //在应用程序的生命周期中，中间件的构造函数只会被调用一次 publicMyMiddleware(RequestDelegate next) { this._next =next; } public asyncTask InvokeAsync(HttpContext context) { await context.Response.WriteAsync("Hello World!"); await_next(context); } }
将自定义中间件配置到请求处理管道中，Startup.cs文件调整：
public voidConfigure(IApplicationBuilder app, IHostingEnvironment env) { app.UseMiddleware<MyMiddleware>(); }
将中间件MyMiddleware改成扩展方法：
新建扩展类MyMiddlewareExtension.cs
usingMicrosoft.AspNetCore.Builder; public static classMyMiddlewareExtension { public static IApplicationBuilder UseMyMiddleware(thisIApplicationBuilder builder) { //使用UseMiddleware将自定义中间件添加到请求处理管道中 return builder.UseMiddleware<MyMiddleware>(); } }
将自定义中间件配置到请求处理管道中，Startup.cs文件调整：
public voidConfigure(IApplicationBuilder app, IHostingEnvironment env) { app.UseMyMiddleware(); }
2.3 自定义中间件类传入初始参数
public classGreetingOption { public string At { get; set; } public string To { get; set; } }
usingMicrosoft.AspNetCore.Http; public classGreetingMiddleware { private readonlyRequestDelegate _next; private readonlyGreetingOption _option; publicGreetingMiddleware(RequestDelegate next, GreetingOption option) { _next =next; _option =option; } public asyncTask Invoke(HttpContext context) { var message = $"Good {_option.At} {_option.To}"; awaitcontext.Response.WriteAsync(message); } }
usingMicrosoft.AspNetCore.Builder; public static classGreetingMiddlewareExtension { public static IApplicationBuilder UseGreetingMiddleware(thisIApplicationBuilder app, GreetingOption option) { return app.UseMiddleware<GreetingMiddleware>(option); } }
public voidConfigure(IApplicationBuilder app, IHostingEnvironment env) { app.UseGreetingMiddleware(newGreetingOption { At = "Morning", To = "Libing" }); }
IMiddleware提供了强类型约束的中间件，其默认实现是MiddlewareFactory，接口定义如下：
public interfaceIMiddleware { Task InvokeAsync(HttpContext context, RequestDelegate next); }
IMiddlewareFactory用于创建IMiddleware实例及对实例进行回收，接口定义：
public interfaceIMiddlewareFactory { publicIMiddleware Create (Type middlewareType); public voidRelease (IMiddleware middleware); }
3.1自定义IMiddleware类型中间件
修改MyMiddleware，实现IMiddleware接口：
usingMicrosoft.AspNetCore.Http; public classMyMiddleware : IMiddleware { public asyncTask InvokeAsync(HttpContext context, RequestDelegate next) { await context.Response.WriteAsync("Hello World!"); awaitnext(context); } }
将自定义中间件配置到请求处理管道中，Startup.cs文件调整：
public voidConfigureServices(IServiceCollection services) { //在服务容器中注册自定义中间件 services.AddSingleton<MyMiddleware>(); } public voidConfigure(IApplicationBuilder app, IHostingEnvironment env) { //使用 UseMiddleware() 把自定义中间件添加到管道中 app.UseMyMiddleware(); }