1 版本

Sleuth版本:3.1.0

ZipKin版本:io.zipkin.brave:5.13.2

Logback版本:1.2.3

2 启动SpringBoot

2.1 构建MDCScopeDecorator属性

brave.baggage.CorrelationScopeDecorator.Builder

2.2 构建对象：MDCScopeDecorator

brave.context.slf4j.MDCScopeDecorator.Builder

2.3 填充属性：traceId和spanId

brave.baggage.CorrelationScopeDecorator.Builder

2.4 traceId和spanId

brave.baggage.BaggageFields

3 请求接口并打印日志

3.1 生成traceId

3.1.1 初始值

brave.Tracer#nextSpan(brave.propagation.TraceContextOrSamplingFlags)

3.1.2 生成span

brave.Tracer#_toSpan

brave.Tracer#_toSpan

3.1.3 生成decorateContext

brave.Tracer#decorateContext(int, long, long, long, long, long, java.util.List)

3.1.4 生成spanId

随机生成数据：
brave.Tracer#nextId

3.1.5 生成traceId

3.1.6 生成localRootId

3.1.7 生成span

brave.http.HttpServerHandler#handleReceive(brave.http.HttpServerRequest)

3.1.8 添加请求属性

org.springframework.cloud.sleuth.instrument.web.servlet.TracingFilter#doFilter

3.2 实际traceId

3.2.1 MDC添加traceId和值

根据MDCScopeDecorator属性个数配置
brave.baggage.CorrelationScopeDecorator.Builder#build

3.2.2 生成最终的traceId

brave.baggage.CorrelationScopeDecorator.Multiple#decorateScope

brave.propagation.TraceContext#traceIdString

public String traceIdString() {String r = traceIdString;if (r == null) {r = toTraceIdString(traceIdHigh, traceId);traceIdString = r;}return r;}

static String toTraceIdString(long traceIdHigh, long traceId) {if (traceIdHigh != 0) {char[] result = RecyclableBuffers.parseBuffer();writeHexLong(result, 0, traceIdHigh);writeHexLong(result, 16, traceId);return new String(result, 0, 32);}return toLowerHex(traceId);}

public static void writeHexLong(char[] data, int pos, long v) {writeHexByte(data, pos + 0, (byte) ((v >>> 56L) & 0xff));writeHexByte(data, pos + 2, (byte) ((v >>> 48L) & 0xff));writeHexByte(data, pos + 4, (byte) ((v >>> 40L) & 0xff));writeHexByte(data, pos + 6, (byte) ((v >>> 32L) & 0xff));writeHexByte(data, pos + 8, (byte) ((v >>> 24L) & 0xff));writeHexByte(data, pos + 10, (byte) ((v >>> 16L) & 0xff));writeHexByte(data, pos + 12, (byte) ((v >>> 8L) & 0xff));writeHexByte(data, pos + 14, (byte) (v & 0xff));}

static void writeHexByte(char[] data, int pos, byte b) {data[pos + 0] = HEX_DIGITS[(b >> 4) & 0xf];data[pos + 1] = HEX_DIGITS[b & 0xf];}

3.3 更新traceId和spanId值

brave.baggage.CorrelationScopeDecorator.Multiple#decorateScope

3.4 更新方法

brave.context.slf4j.MDCScopeDecorator.MDCContext#update

3.5 添加MDCAdapter

org.slf4j.MDC#put

3.6 logbackMDCAdapter添加traceId

ch.qos.logback.classic.util.LogbackMDCAdapter#put

3.7 threadLocal中生成span

brave.propagation.ThreadLocalCurrentTraceContext#newScope

3.8 路径过滤

org.springframework.cloud.sleuth.instrument.web.servlet.TracingFilter#doFilter

3.9 输出日志

3.10 传输traceId和spanId

ch.qos.logback.classic.util.LogbackMDCAdapter#duplicateAndInsertNewMap

4 日志中生成traceId和spanId

5 小结

• SpringBoot启动时在zipkin的包中配置MDCScopeDecorator属性，添加traceId和spanId；
• Sleuth版本:3.1.0：生成traceId和spanId直接使用traceId和spanId获取，日志格式为：[traceId=%X{traceId:-}, spanId=%X{spanId:-}]
• Logback天然配置MDC，通过LogbackMDCAdapter最终填充traceId和spanId值。

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