如何从控制器获取HttpContext

不,这不是正确的方法。您需要使用Filter或中间件来完成。HttpContext类在控制器的构造函数中始终为null

示例中间件代码(用于日志记录)

你可以在这里做任何事情,比如读饼干什么的

public class LoggingMiddleware
{
    private static readonly TelemetryConfiguration telemetryConfiguration = TelemetryConfiguration.CreateDefault();
    private readonly TelemetryClient telemetryClient;
    private IConfiguration configuration;
    private readonly RecyclableMemoryStreamManager _recyclableMemoryStreamManager;
    private readonly string appName;
    private readonly bool loggingEnabled;

    private readonly RequestDelegate _next;

    public LoggingMiddleware(RequestDelegate next, IConfiguration config)
    {
        _next = next;
        configuration = config;
        _recyclableMemoryStreamManager = new RecyclableMemoryStreamManager();
        telemetryConfiguration.InstrumentationKey =  configuration.GetValue<string>("ApplicationInsights:InstrumentationKey");
        telemetryClient = new TelemetryClient(telemetryConfiguration);
        appName = configuration.GetValue<string>("AppName");
        loggingEnabled = configuration.GetValue<bool>("Logging:LogRequestResponse"); 
    }

    public async Task Invoke(HttpContext httpContext)
    {
        if(loggingEnabled)
        {
            await LogRequest(httpContext);
            await LogResponse(httpContext);
        }
    }

    private async Task LogRequest(HttpContext context)
    {
        context.Request.EnableBuffering();

        await using var requestStream = _recyclableMemoryStreamManager.GetStream();
        await context.Request.Body.CopyToAsync(requestStream);

        string correlationId = context.Request.Headers.Keys.FirstOrDefault(h => h.ToLower() == "correlationid");
        if (correlationId == null) correlationId = string.Empty;
        if (context.Request.Path != "/")
        {
            telemetryClient.TrackEvent($"{appName}-RequestMiddleware", new Dictionary<string, string>
            {
                { "AppName", appName },
                { "CorrelationId" , correlationId },
                { "Method" , context.Request.Method },
                { "Scheme", context.Request.Scheme},
                { "Host", context.Request.Host.Value },
                { "Path", context.Request.Path },
                { "QueryString", context.Request.QueryString.Value },
                { "Request Body", ReadStreamInChunks(requestStream) }

            });
        }
        context.Request.Body.Position = 0;
    }

    private static string ReadStreamInChunks(Stream stream)
    {
        const int readChunkBufferLength = 4096;

        stream.Seek(0, SeekOrigin.Begin);

        using var textWriter = new StringWriter();
        using var reader = new StreamReader(stream);

        var readChunk = new char[readChunkBufferLength];
        int readChunkLength;

        do
        {
            readChunkLength = reader.ReadBlock(readChunk,
                                               0,
                                               readChunkBufferLength);
            textWriter.Write(readChunk, 0, readChunkLength);
        } while (readChunkLength > 0);

        return textWriter.ToString();
    }

    private async Task LogResponse(HttpContext context)
    {
        var originalBodyStream = context.Response.Body;

        await using var responseBody = _recyclableMemoryStreamManager.GetStream();
        context.Response.Body = responseBody;

        await _next(context);

        context.Response.Body.Seek(0, SeekOrigin.Begin);
        var text = await new StreamReader(context.Response.Body).ReadToEndAsync();
        context.Response.Body.Seek(0, SeekOrigin.Begin);
        if (context.Request.Path != "/")
        {
            telemetryClient.TrackEvent($"{appName}-ResponseMiddleware", new Dictionary<string, string> {
                {"Scheme", context.Request.Scheme},
                { "AppName", appName },
                {"Host", context.Request.Host.Value},
                {"Path" , context.Request.Path},
                {"QueryString", context.Request.QueryString.Value},
                {"Response Body" , text}
                });
        }
       await responseBody.CopyToAsync(originalBodyStream);
    }
}


// Extension method used to add the middleware to the HTTP request pipeline.
public static class LoggingMiddlewareExtensions
{
    public static IApplicationBuilder UseLoggingMiddleware(this IApplicationBuilder builder)
    {
        return builder.UseMiddleware<LoggingMiddleware>();
    }
}

不,你不能这样做,控制器构造函数是危险区域(除非你知道自己在做什么),应该只用于DI。

相反,您应该看看自定义中间件: https://docs.microsoft.com/en-us/aspnet/core/fundamentals/middleware/write?view=aspnetcore-3.1

有关asp.net核心生命周期的更多信息: https://www.c-sharpcorner.com/article/asp-net-core-mvc-request-life-cycle/