中间件是一种装配到应用管道以处理请求和相应的软件.每个软件都可以:
1.选择是否将请求传递到管道中的下一个组件;
2.可在调用管道中的下一个组件前后执行工作.
管道由 IApplicationBuilder 创建:
每个委托都可以在下一个委托前后执行操作,.此外,委托还可以决定不将请求传递给下一个委托,这就是对请求管道进行短路.通常需要短路,是因为这样可以避免不必要的工作.比如:
1.静态文件中间件可以返回静态文件请求并使管道的其余部分短路;
2.现在管道中调用异常处理委托,以便他们可以捕获在管道的后期阶段所发生的异常.
委托的添加方式一共有3种:
1.Run
该方法的XML注释是这样写的:
Adds a terminal middleware delegate to the application‘s request pipeline.向应用程序请求管道添加一个终端中间件.
通俗来讲,意思就是该方法添加的委托,会使"请求管道短路",不管该委托是否提前响应都会短路.比如下面代码中标红的部分,不管有没有这一句代码,下面的所有代码都不会执行.
???????public void Configure(IApplicationBuilder app, IHostingEnvironment env) ???????{ ???????????app.Run(async context => ???????????{ ???????????????await context.Response.WriteAsync("Hello World!"); ???????????}); ???????????//下面的都不会执行了,因为上面的委托已经终止了管道,或者说:"已经让管道短路了" ?????????... ?????????}2.Use
该方法的XML注释是这样写的:
Adds a middleware delegate defined in-line to the application‘s request pipeline.和上面的 Run 方法相比,少了"terminal".意义就已经很明显了.
???????????????//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. ???????????????//通常可在下一个委托前后执行操作，如以下示例 ???????????????app.Use(async (context, next) => ???????????????{ ???????????????????var name = context.Request.Query["name"]; ???????????????????if (!string.IsNullOrWhiteSpace(name)) ???????????????????{ ???????????????????????await context.Response.WriteAsync($"hello world , {name}"); ???????????????????} ???????????????????await next.Invoke(); ???????????????});请求一:
请求二:
3.Map
根据给定请求路径的匹配项来创建请求分支.如果请求路径以给定的路径开头,则执行分支,如红色部分代码
???????public void Configure(IApplicationBuilder app, IHostingEnvironment env) ???????{ ???????????//Map ???????????app.Map(new PathString("/map1"), MapTest1); ???????????app.Map("/map2", MapTest2); ???????????app.MapWhen(context => !string.IsNullOrWhiteSpace(context.Request.Query["name"]), MapTest3); ???????????if (env.IsDevelopment()) ???????????{ ???????????????app.UseDeveloperExceptionPage(); ???????????} ???????????else ???????????{ ???????????????app.UseHsts(); ???????????} ???????????app.UseHttpsRedirection(); ???????????app.UseMvc(); ???????} ???????public void MapTest1(IApplicationBuilder app) ???????{ ???????????app.Run(async context => { await context.Response.WriteAsync("this is maptest1"); }); ???????} ???????public void MapTest2(IApplicationBuilder app) ???????{ ???????????app.Run(async context => { await context.Response.WriteAsync("this is maptest2"); }); ???????} ???????public void MapTest3(IApplicationBuilder app) ???????{ ???????????app.Run(async context => { await context.Response.WriteAsync("this is maptest3"); }); ???????}另外,Map 支持嵌套 : app.Map("/map2", builder => { builder.Map("/map22", MapTest22); });
封装中间件
在实际运用过程中,我们通常将中间件封装在类中,然后通过扩展方法公开出来.方式有两种:
一.启动时构造
1.自定义中间件
???public class MyMiddleware ???{ ???????private readonly RequestDelegate _next; ???????public MyMiddleware(RequestDelegate next) ???????{ ???????????_next = next; ???????} ???????//方法名必须是 Invoke 或者 InvokeAsync ???????public async Task InvokeAsync(HttpContext context) ???????{ ???????????var name = context.Request.Query["name"]; ???????????if (!string.IsNullOrWhiteSpace(name)) ???????????{ ???????????????await context.Response.WriteAsync($"hello world,{name}"); ???????????} ???????????else ???????????{ ???????????????await _next(context); ???????????} ???????} ???}2.通过扩展方法公开
???public static class MyMiddlewareExtensions ???{ ???????public static IApplicationBuilder UseMyMiddleware(this IApplicationBuilder app) ???????{ ???????????return app.UseMiddleware<MyMiddleware>(); ???????} ???}3.调用自定义的中间件.
???????public void Configure(IApplicationBuilder app, IHostingEnvironment env) ???????{ ???????????if (env.IsDevelopment()) ???????????{ ???????????????app.UseDeveloperExceptionPage(); ???????????} ???????????else ???????????{ ???????????????app.UseHsts(); ???????????} ???????????//调用自制中间件 ???????????app.UseMyMiddleware(); ???????????app.UseHttpsRedirection(); ???????????app.UseMvc(); ???????}这种方式编写的中间件,是在web应用启动时构造的,而不是按请求构造的,因此相当于单例.
所以,如果想正确使用中间件依赖项的生存期,则需要将这些依赖项添加到 Invoke 或者 InvokeAsync 方法的入参里面,如:
???public class Person ???{ ???????public string Name { get; set; } ???} ???public class Startup ???{ ???????...other codes ???????????public void ConfigureServices(IServiceCollection services) ???????{ ???????????services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2); ???????????//services.AddSingleton(new Person() { Name = "admin" }); ???????????//services.AddTransient<Person>(); ???????????services.AddScoped<Person>(); ???????} ???????...other codes ???} ???????//方法名必须是 Invoke 或者 InvokeAsync ???????public async Task InvokeAsync(HttpContext context, Person person) ???????{ ???????????var name = context.Request.Query["name"]; ???????????if (!string.IsNullOrWhiteSpace(name)) ???????????{ ???????????????await context.Response.WriteAsync($"hello world,{name},the person`s hashcode is {person.GetHashCode()}"); ???????????} ???????????else ???????????{ ???????????????await context.Response.WriteAsync($"hello world,{person.Name},the person`s hashcode is {person.GetHashCode()}"); ???????????} ???????}二.按请求激活
该方式需要自定义中间件实现 IMiddleware 接口.
???public class MyMiddleware : IMiddleware ???{ ???????private readonly Person _person; ???????public MyMiddleware(Person person) ???????{ ???????????_person = person; ???????} ???????public async Task InvokeAsync(HttpContext context, RequestDelegate next) ???????{ ???????????var name = context.Request.Query["name"]; ???????????if (!string.IsNullOrWhiteSpace(name)) ???????????{ ???????????????await context.Response.WriteAsync($" {name} , hello ! the model`s hashcode is {this.GetHashCode()}"); ???????????} ???????????else ???????????{ ???????????????await context.Response.WriteAsync($" {_person.Name} hello ! the model`s hashcode is {this.GetHashCode()}"); ???????????} ???????} ???}扩展方法的代码没变:
???public static class MyMiddlewareExtensions ???{ ???????public static IApplicationBuilder UseMyMiddleware(this IApplicationBuilder app) ???????{ ???????????return app.UseMiddleware<MyMiddleware>(); ???????} ???}调用自制的中间件:
???public class Startup ???{ ???????public void ConfigureServices(IServiceCollection services) ???????{ ???????????services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2); ???????????//将中间件对象按我们需要的生存期注入到容器中. ???????????//services.AddTransient<MyMiddleware>(); ???????????//services.AddScoped<MyMiddleware>(); ???????????services.AddSingleton<MyMiddleware>();
?services.AddSingleton(new Person { Name = "admin" }); ???????} ???????public void Configure(IApplicationBuilder app, IHostingEnvironment env) ???????{ ???????????//注册我们的中间件 ???????????app.UseMyMiddleware(); ???????????app.UseHttpsRedirection(); ???????????app.UseMvc(); ???????} ???}...未完待续
ASP.NET Core 2.2 基础知识(二) 中间件
原文地址：https://www.cnblogs.com/lonelyxmas/p/10217731.html