本文自定义一个NLog Layout Renderer（显示HttpClient请求的耗时）
什么是Layout Renderer？
nlog日志上输出的特定字段，便于检索和分类。
代码语言：javascript复制# 截取自nlog.config配置文件
<target name="bce-request" xsi:type="File"
layout="${date:format=yy/MM/dd HH:mm:ss} [${level}].[${logger}].[${threadid}}].[${elapse}]${newline}${message} ${exception:format=tostring}"
fileName="${logDir}/bce-request.log" encoding="utf-8"/>以上配置输出如下日志:
代码语言：javascript复制19/12/08 22:46:29 [Info].[System.Net.Http.HttpClient.bce-request.LogicalHandler].[6}].[415.2504]HTTP request http://localhost:5000/v1/eqid/e741e8d600151edc000000035decf3bf after 415.2504ms end -OK 19/12/08 22:47:15 [Info].[System.Net.Http.HttpClient.bce-request.LogicalHandler].[40}].[80.2951]HTTP request http://localhost:5000/v1/eqid/2a41e8d600151edc000000028decf3bf after 80.2951ms end -OK 19/12/08 22:48:06 [Info].[System.Net.Http.HttpClient.bce-request.LogicalHandler].[43}].[36.8624]HTTP request http://localhost:5000/v1/eqid/1a41e8d600151edc000000028decf3bf after 36.8624ms end -OK头脑风暴
nlog所有的日志Render依赖日志写入时的信息， 因此我们在写入日志时附带该Renderer值， 然后配置nlog显示日志时提取该Renderer值。
1
写入日志时，为Message传入参数{Url}, {Elapse}, {StatusCode}, 这三个参数值可被提取作为 Renderer
代码语言：javascript复制public class CustomHttpMessageHandler : DelegatingHandler { private readonly ILogger _logger;
public AttachTraceIdScopeHttpMessageHandler(ILogger logger) { _logger = logger ?? throw new ArgumentNullException(nameof(logger)); }
protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) { if (request == null) { throw new ArgumentNullException(nameof(request)); }
var stopwatch = Stopwatch.StartNew(); var response = await base.SendAsync(request, cancellationToken); stopwatch.Stop(); _logger.Log(LogLevel.Information, new EventId(101, "Request End"), "HTTP request {Url} after {Elapse}ms end -{StatusCode}", request.RequestUri, stopwatch.Elapsed.TotalMilliseconds, response.StatusCode); return response; } }2
添加自定义LayOutRenderer
① 简单的lambda方式，
② 我们采用稍灵活的自定义类方式：
关键点是实现LayoutRenderer的抽象方法Append, 从LogEventInfo中提出Renderer值：
代码语言：javascript复制[LayoutRenderer("elapse")] public class ElapseLayoutRenderer : LayoutRenderer { protected override void Append(StringBuilder builder, LogEventInfo logEvent) { builder.Append(logEvent.Properties["Elapse"].ToString()); } }# 参数Url、Elapse、StatusCode均可在LogEventInfo.Prpperties键值对提取
3
按照文档的要求，尽早注册自定义Nlog Layout Renderer：
代码语言：javascript复制public static void Main(string[] args){ LayoutRenderer.Register<ElapseLayoutRenderer>("elapse"); ......}END
