出现这个问题的原因是Swagger的配置可能不完整或不正确。为了解决这个问题，可以按照以下步骤：

1. 在Startup.cs里添加Swagger服务

services.AddSwaggerGen(c => { c.SwaggerDoc("v1", new OpenApiInfo { Title = "My API", Version = "v1" }); });

2. 配置Swagger到应用程序的中间件

app.UseSwagger();

//启用SwaggerUI中间件 app.UseSwaggerUI(c => { c.SwaggerEndpoint("/swagger/v1/swagger.json", "My API V1"); });

3. 确保Swagger端点可访问

确保访问/swagger可以看到Swagger UI并且访问/swagger/v1/swagger.json可以看到Swagger JSON。

安装Swagger生成器（Swashbuckle.AspNetCore）NuGet包，启用中间件并创建Swagger端点的代码示例如下：

using System; using System.Collections.Generic; using System.Linq; using System.Threading.Tasks; using Microsoft.AspNetCore.Builder; using Microsoft.AspNetCore.Hosting; using Microsoft.AspNetCore.Http; using Microsoft.Extensions.DependencyInjection; using Microsoft.Extensions.Hosting; using Microsoft.OpenApi.Models;

namespace MyProject { public class Startup { public void ConfigureServices(IServiceCollection services) { services.AddControllers();

        services.AddSwaggerGen(c =>
        {
            c.SwaggerDoc("v1", new OpenApiInfo { Title = "My API", Version = "v1" });
        });
    }

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }

        app.UseHttpsRedirection();

        app.UseRouting();

        app.UseAuthorization();

        app.UseEndpoints(endpoints =>
        {
            endpoints.MapControllers();
        });

        app.UseSwagger();

        app.UseSwaggerUI(c =>
        {
            c.SwaggerEndpoint("/swagger/v1/swagger.json", "My API V1");
        });
    }
}

}

通过以上步骤，可以成功启用AspNetCore Swagger并且JSON和UI返回终点404错误的问题也能得到解决。