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

1.问题出现

某年某月某日，把webapi开发完了，也通过了swagger进行了单元测试。

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:\工作事项\code\dev-push\Alipush\AliMobilePush.Webapi\Startup.cs:line 75at 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)

配置文件读出来为null，为什么？

2.难道是非管理员,权限不够？

切换至管理员，运行上述命令，还是报错。

3.无意间解决

cd publish
dotnet xx.Webapi.dll

就能读到了，这是为什么，根据上述命令的差异，大概能猜测到应该是路径不同，导致读取appsetting.json失败。

4.原来是这样

dotnet run，应该会根据env.ContentRootPath（env 的类型是IHostingEnvironment ）来读取配置文件 appsettings.Production.json 和 appsettings.json文件，ContentRootPath 属性得到的值为当前启动命令的目录，而不是dll所在的目录，所以应在发布项目dll所在的目录执行 dotnet xx.dll，否则会导致配置文件里面的参数读取不到。请看源码和命令对比：

// Host.CreateDefaultBuilder(args)//源码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);}})

5.参考链接

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

马上就是饭点了，今天怎么吃？