【日常排雷】 .Net core 生產環境appsetting讀取失敗

關鍵詞System.ArgumentNullException: String reference not set to an instance of a String. (Parameter 's')

1.問題出現

某年某月某日，把webapi開發完了，也通過了swagger進行了單元測試。

dotnet build
dotnet publish -o publish
dotnet .\publish\xx.Webapi.dll

然后String reference not set to an instance of a String. (Parameter 's')

fail: Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware[1]
      An unhandled exception has occurred while executing the request.
System.ArgumentNullException: String reference not set to an instance of a String. (Parameter 's')
   at System.Text.Encoding.GetBytes(String s)
   at AliMobilePush.Webapi.Startup.<ConfigureServices>b__5_2(JwtBearerOptions option) in E:\工作事項\code\dev-push\Alipush\AliMobilePush.Webapi\Startup.cs:line 75
   at Microsoft.Extensions.Options.ConfigureNamedOptions`1.Configure(String name, TOptions options)
   at Microsoft.Extensions.Options.OptionsFactory`1.Create(String name)
   at Microsoft.Extensions.Options.OptionsMonitor`1.<>c__DisplayClass11_0.<Get>b__0()
   at System.Lazy`1.ViaFactory(LazyThreadSafetyMode mode)
   at System.Lazy`1.ExecutionAndPublication(LazyHelper executionAndPublication, Boolean useDefaultConstructor)
   at System.Lazy`1.CreateValue()
   at System.Lazy`1.get_Value()
   at Microsoft.Extensions.Options.OptionsCache`1.GetOrAdd(String name, Func`1 createOptions)
   at Microsoft.Extensions.Options.OptionsMonitor`1.Get(String name)
   at Microsoft.AspNetCore.Authentication.AuthenticationHandler`1.InitializeAsync(AuthenticationScheme scheme, HttpContext context)
   at Microsoft.AspNetCore.Authentication.AuthenticationHandlerProvider.GetHandlerAsync(HttpContext context, String authenticationScheme)
   at Microsoft.AspNetCore.Authentication.AuthenticationService.AuthenticateAsync(HttpContext context, String scheme)
   at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
   at Swashbuckle.AspNetCore.SwaggerUI.SwaggerUIMiddleware.Invoke(HttpContext httpContext)
   at Swashbuckle.AspNetCore.Swagger.SwaggerMiddleware.Invoke(HttpContext httpContext, ISwaggerProvider swaggerProvider)
   at Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware.<Invoke>g__Awaited|6_0(ExceptionHandlerMiddleware middleware, HttpContext context, Task task)

配置文件讀出來為null，為什么？

2.難道是非管理員,權限不夠？

切換至管理員，運行上述命令，還是報錯。

3.無意間解決

cd publish
dotnet xx.Webapi.dll

就能讀到了，這是為什么，根據上述命令的差異，大概能猜測到應該是路徑不同，導致讀取appsetting.json失敗。

4.原來是這樣

dotnet run，應該會根據env.ContentRootPath（env 的類型是IHostingEnvironment ）來讀取配置文件 appsettings.Production.json 和 appsettings.json文件，ContentRootPath 屬性得到的值為當前啟動命令的目錄，而不是dll所在的目錄，所以應在發布項目dll所在的目錄執行 dotnet xx.dll，否則會導致配置文件里面的參數讀取不到。請看源碼和命令對比：

// Host.CreateDefaultBuilder(args)

//源碼Host.cs           
builder.ConfigureAppConfiguration((hostingContext, config) =>
            {
                var env = hostingContext.HostingEnvironment;

                config.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
                      .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true, reloadOnChange: true);

                if (env.IsDevelopment() && !string.IsNullOrEmpty(env.ApplicationName))
                {
                    var appAssembly = Assembly.Load(new AssemblyName(env.ApplicationName));
                    if (appAssembly != null)
                    {
                        config.AddUserSecrets(appAssembly, optional: true);
                    }
                }

                config.AddEnvironmentVariables();

                if (args != null)
                {
                    config.AddCommandLine(args);
                }
            })

5.參考鏈接

https://www.cnblogs.com/DHclly/p/9606866.html

https://www.netnr.com/home/list/115

https://github.com/dotnet/extensions.git

https://my.oschina.net/u/4364008/blog/3205437

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作者：Garfield

同步更新至個人博客:http://www.randyfield.cn/

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