.Net Core控制台在微服务中实现后台任务

原理解释看官网

主要实现代码

该代码主要实现获取微信小程序的访问凭证，并保存到Sqlite数据库中。
主要使用了以下组件

Microsoft.CSharp //用于处理动态类型
NLog.Extensions.Logging //日志
Newtonsoft.Json //json序列号和反序列化，可以使用dynamic
Microsoft.Extensions.Hosting //重中之重，实现后台任务关键
Microsoft.Extensions.Http  //实现HttpClient
Microsoft.EntityFrameworkCore.Design
Microsoft.EntityFrameworkCore.Sqlite
Microsoft.EntityFrameworkCore.Tools

program.cs主要代码

namespace ConsoleAppWithDI
{
    class Program
    {
        static Task Main(string[] args)=>
            CreateHostBuilder(args).Build().RunAsync();
        

         static IHostBuilder CreateHostBuilder(string[] arg) =>
            Host.CreateDefaultBuilder(arg)
                .ConfigureLogging(logging =>
                {
                    logging.ClearProviders();
                    logging.SetMinimumLevel(LogLevel.Information);
                    logging.AddNLog(new NLogProviderOptions
                    {
                        CaptureMessageProperties = true,
                        CaptureMessageTemplates = true
                    });
                })
                .ConfigureServices((hostContext,services)=> {
                    services.AddHostedService<ExampleHostedService>();
                    services.AddHttpClient();
                    services.AddDbContext<ExampleDbContext>(options => options.UseSqlite("Data Source=db/dataBase.db"));

                });
    }
}

继承BackgroundService类的ExampleHostedService :

namespace ConsoleAppWithDI
{
    class ExampleHostedService : BackgroundService
    {
        private readonly ILogger _logger;
        private readonly HttpClient _httpClient;
        private readonly ExampleDbContext _context;
        public ExampleHostedService(ILogger<ExampleHostedService> logger, HttpClient httpClient, IServiceScopeFactory scopeFactory )
        {
        	//依赖注入获取实例
            _logger = logger;
            _httpClient = httpClient;
            _context = scopeFactory.CreateScope().ServiceProvider.GetRequiredService<ExampleDbContext>();//控制台不能像asp.net那样很方便的获取_context；
        }
        protected override async Task<Task> ExecuteAsync(CancellationToken stoppingToken)
        {
           var token= _context.AppAccessTokens.OrderByDescending(x => x.Time).FirstOrDefault();
            bool isExpired = true;
            if(token!=null)
            {
            	//比较时间
                TimeSpan timeSpan1 = new TimeSpan(token.Time.Ticks);
                TimeSpan timeSpan2 = new TimeSpan(DateTime.Now.Ticks);
                TimeSpan timeSpan3 = timeSpan2 - timeSpan1;
                if (timeSpan3.TotalSeconds < token.ExpiresIn-600)
                {
                    isExpired = false;
                }
            }

            if (isExpired)
            {
                DateTime now = DateTime.Now;
                var url = $"https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid=你的appid&secret=你的secret";
                
                var response = await _httpClient.GetAsync(url);
                //获取请求到数据，并转化为字符串
                var result = response.Content.ReadAsStringAsync().Result;                
                var newToken= JsonConvert.DeserializeObject<dynamic>(result);

                if (newToken.access_token!=null)
                {
                    if (token != null)//如果已存在则更新，否则添加
                    {
                        token.AccessToken = newToken.access_token;
                        token.ExpiresIn = newToken.expires_in;
                        token.Time = now;
                        _context.AppAccessTokens.Update(token);
                    }
                    else
                    {
                        _context.AppAccessTokens.Add(new AppAccessToken
                        {
                            AccessToken = newToken.access_token,
                            ExpiresIn = newToken.expires_in,
                            Time = now
                        });
                    }
                    _context.SaveChanges();
                }
                
            }

            
            return Task.CompletedTask;
        }
    }
}

ExampleDbContext类

namespace ConsoleAppWithDI.Models
{
    class ExampleDbContext: DbContext
    {
        public DbSet<AppAccessToken> AppAccessTokens { get; set; }
        public ExampleDbContext(DbContextOptions<ExampleDbContext> options)
            : base(options)
        { }
        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<AppAccessToken>()
                .Property(x => x.ExpiresIn)
                .HasDefaultValue(7200);

            modelBuilder.Entity<AppAccessToken>()
                .Property(x => x.Time)
                .HasDefaultValueSql("datetime('now', 'localtime')");//时间默认值 sqlServer 使用  GETDATE()
        }
    }
}

完整例子