asp.net core startup配置文件

startup

配置入口：

WebHost.CreateDefaultBuilder(args)
    .UseStartup<Startup>()
    .Build();

Startup仅仅是个约定的名字，完全可以换成其他名字

两个重要的方法：

• public void ConfigureServices(IServiceCollection services)

  可选的方法。IServiceCollection通过DI注入实例

• public void Configure(IApplicationBuilder app, IHostingEnvironment env)

  必须方法。IApplicationBuilder、IHostingEnvironment等都是通过DI注入实例

startup类的主要作用是提供用一个便捷的配置入口，主要提供ConfigureServices和ConfigureServices两个方法。其本质是如下代码所示：

WebHost.CreateDefaultBuilder ()
    .ConfigureServices (services =>
        services.AddSingleton<IComponent, ComponentInstance> ()
    )
    .Configure (app => {
        var component = app.ApplicationServices.GetRequiredService<IComponent> ();
        app.Run (async (context) =>
            await context.Response.WriteAsync ($"Name is {component.Name}")
        );
    })
    .Build ();

由此可见，startup只是提供了ConfigureServices和Configure两个重要的方法而已。除了这两个方法外，也可放置其他可用的方法，如 Configure[Environment]、ConfigureServices[Environment]。ConfigureServices先于Configure执行。因为Configure的回调函数只接受一个IApplicationBuilder,因此需要手动调用app.ApplicationServices.GetRequiredService<IComponent> (),以获取依赖注入的实例。

请求管道（pipeline）

主要包括`run`，`use`，`Map`，`MapWhen`几种方法。

• Use

  拦截管道，注入自己的逻辑后可直接返回，也可调用next()方法继续执行下个管道方法。use和run都接受一个RequestDelegate作为唯一参数，RequestDelegate的参数是HttpContext。

  public void Configure (IApplicationBuilder app) {
      app.Use (async (context, next) => {
          if (context.Request.Path == "/foo") {
              await context.Response.WriteAsync ($"Welcome to Foo");
          } else {
              await next ();
          }
      });
      app.Use (async (context, next) => {
          if (context.Request.Path == "/bar") {
              await context.Response.WriteAsync ($"Welcome to Bar");
          } else {
              await next ();
          }
      });
      app.Run (async (context) =>
          await context.Response.WriteAsync ($"Welcome to the default")
      );
  }
  

• Run

  最后执行。直接打断整个请求，立即返回，因此一般放置于最后。

  app.Run (async (context) =>
      await context.Response.WriteAsync ($"Name is {component.Name}")
  );

• Map, MapWhen

  app.Map ("/foo",
      config =>
      config.Use (async (context, next) =>
          await context.Response.WriteAsync ("Welcome to /foo")
      )
  );
  app.MapWhen (
      context =>
      context.Request.Method == "POST" &&
      context.Request.Path == "/bar",
      config =>
      config.Use (async (context, next) =>
          await context.Response.WriteAsync ("Welcome to POST /bar")
      )
  );

自定义中间件

• 定义中间件类：

  public class RequestLogMiddleware
  {
      private RequestDelegate _next;
      public RequestLogMiddleware (RequestDelegate requestDelegate)
      {
          _next = requestDelegate;
      }
  
      public async Task Invoke(HttpContext context)
      {
          Console.WriteLine($"request path: {context.Request.Path}\r\n");
          await context.Response.WriteAsync($"request path: {context.Request.Path}\r\n");
  
          await _next.Invoke(context);
  
          Console.WriteLine("finish request!");
          await context.Response.WriteAsync("finish request!\r\n");
      }
  }

• 添加IApplicationBuilder扩展方法

  public static IApplicationBuilder UseRequestLogger(this IApplicationBuilder builder)
  {
      return builder.UseMiddleware<RequestLogMiddleware>();
  }

• Configure()方法中使用中间件：

  public void Configure(IApplicationBuilder app, IHostingEnvironment env)
  {
      if (env.IsDevelopment())
      {
          app.UseDeveloperExceptionPage();
      }
  
      app.UseRequestLogger(); // 自定义中间件
  
      app.Use(async (context, next) =>
      {
          await context.Response.WriteAsync("in use1 middleware!\r\n");
          await next();
          await context.Response.WriteAsync("out use1 middleware!\r\n");
  
      });
      app.Use(async (context, next) =>
      {
          await context.Response.WriteAsync("in use2 middleware!\r\n");
          await next();
          await context.Response.WriteAsync("out use2 middleware!\r\n");
  
      });
  
      app.Run(async (context) =>
      {
          await context.Response.WriteAsync("in run middleware!\r\n");
      });
  }

• 执行结果：

  request path: /api/values
  in use1 middleware!
  in use2 middleware!
  in run middleware!
  out use2 middleware!
  out use1 middleware!
  finish request!