先决条件

首先要安装最新版的vs2022才能开发.net6项目。我这里没有直接去.net5项目上做更改，而是用vs2022新建一个.net6的asp.netcore web空项目，然后再把.net5的代码copy过来

变化点

.net6最大的变化在于Startup.cs和 Program.cs文件

最小宿主模型：

大大减少了创建应用程序所需的文件和代码行数。只有一个文件需要四行代码。
Startup.cs将和 Program.cs 合并到单个 Program.cs 文件中。
使用顶级语句来最大程度地减少应用程序所需的代码。
使用全局 using 指令消除或最大程度地减少所需的 using 语句行数。

以上是微软官方的话语，其实就是微软化繁为简，把之前startup里的代码又放回了program里面，同时为了省事把main函数以及花括号通通删掉，namespace也做了优化，最终我们看到的program变成了这样

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
builder.Services.AddRazorPages();

var app = builder.Build();

// Configure the HTTP request pipeline.
if (!app.Environment.IsDevelopment())
{
   app.UseExceptionHandler("/Error");
   // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
   app.UseHsts();
}

app.UseHttpsRedirection();
app.UseStaticFiles();

app.UseRouting();

app.UseAuthorization();

app.MapRazorPages();

app.Run();

在我们的.net5项目里，我们使用了NewtonsoftJson组件以及IHttpContextAccessor来获取httpcontext,startup类的代码如下

public void ConfigureServices(IServiceCollection services)
        {
            services.AddControllers().AddNewtonsoftJson(options =>
            { 
                // 设置时间格式
                options.SerializerSettings.DateFormatString = "yyyy-MM-dd HH:mm:ss"; 
                //忽略null值
                options.SerializerSettings.NullValueHandling = NullValueHandling.Ignore;
            }); 
            services.AddMvc();
            services.AddHealthChecks();
            //注入HttpContextAccessor
            services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();
        }
     public void Configure(IApplicationBuilder app, IWebHostEnvironment env, IHttpContextAccessor accessor)
        {
            //设置HttpContextAccessor实例
            HttpContextHelper._accessor = accessor;
            ... 
    }

.net6的方案

根据微软官方说法

ConfigureServices 已替换为 WebApplication.Services 。
builder.Build() 返回配置 WebApplication 为该变量的 app 。 Configure 使用对相同服务的配置调用将替换为 app 。
于是我们的Program.cs代码改为

builder.Services.AddControllers().AddNewtonsoftJson(options =>
{ 
    // 设置时间格式
    options.SerializerSettings.DateFormatString = "yyyy-MM-dd HH:mm:ss"; 
    //忽略null值
    options.SerializerSettings.NullValueHandling = NullValueHandling.Ignore;
}); 
//注入HttpContextAccessor
builder.Services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();
...
var app = builder.Build();
//初始化HttpContextAccessor实例
var httpContextAccessor = app.ApplicationServices.GetRequiredService<IHttpContextAccessor>();
HttpContextHelper._accessor = httpContextAccessor;

当然我们可以通过扩展方法来优化下代码

 
    public static void AddHttpContextAccessor(this IServiceCollection services)
    {
        services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();
    } 
    public static IApplicationBuilder UseStaticHttpContext(this IApplicationBuilder app)
    {
        var httpContextAccessor = app.ApplicationServices.GetRequiredService<IHttpContextAccessor>();
        HttpContextHelper._accessor = httpContextAccessor;
        return app;
    }

通过以上改造,.net6项目正常运行了，后面就是把.net5项目的业务代码copy到新项目即可
最终的代码如下

 
using Microsoft.AspNetCore.ResponseCompression;
using Swashbuckle.AspNetCore.Swagger;

var builder = WebApplication.CreateBuilder(args); 
// Add services to the container.
builder.Services.AddControllers().AddNewtonsoftJson(options =>
{ 
    // 设置时间格式
    options.SerializerSettings.DateFormatString = "yyyy-MM-dd HH:mm:ss"; 
    //忽略null值
   options.SerializerSettings.NullValueHandling = NullValueHandling.Ignore;
}); 
builder.Services.AddResponseCompression(options =>
{
    options.Providers.Add<GzipCompressionProvider>();
}); 
builder.Services.AddMvc();
builder.Services.AddHealthChecks();
// Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen(c =>
{
    c.SwaggerDoc("v1", new  Microsoft.OpenApi.Models.OpenApiInfo { Title = "My-API", Version = "v1" });
    var basePath = Path.GetDirectoryName(typeof(Program).Assembly.Location); 
    var xmlPath = Path.Combine(basePath, "SwaggerDemo.xml");
    c.IncludeXmlComments(xmlPath);
});

//注入HttpContextAccessor
builder.Services.AddHttpContextAccessor(); 
var app = builder.Build(); 
// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI(c =>
    {
        c.SwaggerEndpoint("/swagger/v1/swagger.json", "My-API");
    });
}

//设置HttpContextAccessor实例
app.UseStaticHttpContext();
...
app.Run();