Mastering ASP.NET Web API

MapWhen()

Works similarly to the Map() method, but with more control over URL, request headers, query strings, and so on. The MapWhen() method returns Boolean after checking any condition from the HttpContext as parameter.

Copy the following code snippet in the Configure method of the Startup class:

    public void Configure(IApplicationBuilder app, IHostingEnvironment env,      ILoggerFactory loggerFactory) 
    { 
      app.Use(async (context, next) => 
      { 
        await context.Response.WriteAsync("Middleware 1 - Map When <br/>"); 
        await next(); 
      }); 
 
      app.MapWhen(context =>         context.Request.Query.ContainsKey("packtquery"), (appbuilder) => 
      { 
        appbuilder.Run(async (context) => 
        { 
          await context.Response.WriteAsync("In side Map When <br/>"); 
        }); 
      }); 
    } 

Running this example will ...