参考链接：
博客园: 在.NET 9中使用Scalar替代Swagger
MSDoc: Use openAPI documents

.NET 9 刚刚发布，默认的 API 模板里，老朋友 Swagger UI 被砍了（好刀法🙄），不过 OpenAPI 的接口文档还在，导入第三方啥的倒是没啥问题。
配合 ApiExplorer 和 .http 文件的内置支持，倒也可以实现交互式的接口测试。
不过老朋友 1 秒不见，甚是想念，不习惯的还是能找回来滴。

.NET9 WebAPI 默认模板

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
// Learn more about configuring OpenAPI at https://aka.ms/aspnet/openapi
builder.Services.AddOpenApi();

var app = builder.Build();

// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
    app.MapOpenApi();
}

var summaries = new[]
{
    "Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"
};

app.MapGet("/weatherforecast", () =>
{
    var forecast = Enumerable.Range(1, 5).Select(index =>
        new WeatherForecast
        (
            DateOnly.FromDateTime(DateTime.Now.AddDays(index)),
            Random.Shared.Next(-20, 55),
            summaries[Random.Shared.Next(summaries.Length)]
        ))
        .ToArray();
    return forecast;
})
.WithName("GetWeatherForecast");

app.Run();

internal record WeatherForecast(DateOnly Date, int TemperatureC, string? Summary)
{
    public int TemperatureF => 32 + (int)(TemperatureC / 0.5556);
}

API 调用

{baseAddress}/weatherforecast

OpenAPI 接口

{baseAddress}/openapi/v1.json

Swagger UI

找回老朋友的步骤很简单啊：

1. 安装 Swashbuckle.AspNetCore.SwaggerUi 包

Install-Package Swashbuckle.AspNetCore.SwaggerUi

2. 配置使用 SwaggerUI

// 省略……

if (app.Environment.IsDevelopment())
{
    app.MapOpenApi();
    
    // 使用 Swagger UI
    app.UseSwaggerUI(options => { options.SwaggerEndpoint("/openapi/v1.json", "v1"); });
}

// 省略……

3. 访问 Swagger 路径（嘿呦，我的老朋友😎）

{baseAddress}/swagger/index.html

Scalar

同时，微软也推荐了另一个替代产品：Scalar，给我感觉更像是简化版的 Postman。使用步骤也很简单啊：

1. 安装 Scalar.AspNetCore 包。

Install-Package Scalar.AspNetCore

2. 配置使用 Scalar

// 省略……

if (app.Environment.IsDevelopment())
{
    app.MapOpenApi();
    
    // 使用 Swagger UI
    app.UseSwaggerUI(options => { options.SwaggerEndpoint("/openapi/v1.json", "v1"); });

    // 使用 Scalar
    app.MapScalarApiReference();
}

// 省略……

3. 访问 Scalar 的路径（嘿嘿，我的新朋友😎）

{baseAddress}/scalar/v1

不得不说，跟 Swagger 的配置简直一模一样啊。

完整代码

最后，奉上完整代码

using Scalar.AspNetCore;

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
// Learn more about configuring OpenAPI at https://aka.ms/aspnet/openapi
builder.Services.AddOpenApi();

var app = builder.Build();

// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
    app.MapOpenApi();
    app.UseSwaggerUI(options => { options.SwaggerEndpoint("/openapi/v1.json", "v1"); });
    app.MapScalarApiReference();
}

var summaries = new[]
{
    "Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"
};

app.MapGet("/weatherforecast", () =>
{
    var forecast = Enumerable.Range(1, 5).Select(index =>
        new WeatherForecast
        (
            DateOnly.FromDateTime(DateTime.Now.AddDays(index)),
            Random.Shared.Next(-20, 55),
            summaries[Random.Shared.Next(summaries.Length)]
        ))
        .ToArray();
    return forecast;
})
.WithName("GetWeatherForecast");

app.Run();

internal record WeatherForecast(DateOnly Date, int TemperatureC, string? Summary)
{
    public int TemperatureF => 32 + (int)(TemperatureC / 0.5556);
}