SpringCloud項目接入Jaeger（下）

一、上篇回顧

以前一篇文章中說到當咱們放棄spring-cloud-sleuth這個組件時，會面臨兩個問題。首先是日誌中沒法顯示traceId和spanId這些鏈路信息，其次是不能在用spring-cloud-sleuth所提供的方式進行鏈路傳值。如今就讓咱們來解決這兩個問題。上篇回顧

二、日誌顯示traceId

spring-cloud-sleuth是將traceId等鏈路信息保存在slf4j的MDC（Mapped Diagnostic Contexts）中，而後經過%X{traceId}這種方式將traceId提取出來，好比打印到控制檯的默認格式是：

%clr(%d{${LOG_DATEFORMAT_PATTERN:-yyyy-MM-dd HH:mm:ss.SSS}}){faint} %clr(%5p [${spring.application.name:-},%X{X-B3-TraceId:-},%X{X-B3-SpanId:-},%X{X-Span-Export:-}]) %clr(${PID:- }){magenta} %clr(---){faint} %clr([%15.15t]){faint} %clr(%-40.40logger{39}){cyan} %clr(:){faint} %m%n${LOG_EXCEPTION_CONVERSION_WORD:-%wEx}}
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opentracing中提供了ThreadLocalScopeManager這個類來管理調用上下文中的Span，咱們能夠繼承該類將traceId設置到MDC中。

public class MDCScopeManager extends ThreadLocalScopeManager {

    @Override
    public Scope activate(Span span, boolean finishOnClose) {
        return new ScopeWrapper(super.activate(span, finishOnClose));
    }

    @Override
    public Scope activate(Span span) {
        return new ScopeWrapper(super.activate(span));
    }

    private static class ScopeWrapper implements Scope {

        private final Scope scope;
        private final String previousTraceId;
        private final String previousSpanId;
        private final String previousParentSpanId;
        private final String previousSampled;

        ScopeWrapper(Scope scope) {
            this.scope = scope;
            this.previousTraceId = lookup("traceId");
            this.previousSpanId = lookup("spanId");
            this.previousParentSpanId = lookup("parentSpanId");
            this.previousSampled = lookup("traceSampled");

            JaegerSpanContext ctx = (JaegerSpanContext) scope.span().context();
            String traceId = ctx.getTraceId();
            String spanId = Long.toHexString(ctx.getSpanId());
            String sampled = String.valueOf(ctx.isSampled());
            String parentSpanId = Long.toHexString(ctx.getParentId());

            replace("traceId", traceId);
            replace("spanId", spanId);
            replace("parentSpanId", parentSpanId);
            replace("traceSampled", sampled);
        }

        @Override
        public void close() {
            this.scope.close();
            replace("traceId", previousTraceId);
            replace("spanId", previousSpanId);
            replace("parentSpanId", previousParentSpanId);
            replace("traceSampled", previousSampled);
        }

        @Override
        public Span span() {
            return this.scope.span();
        }
    }

    private static String lookup(String key) {
        return MDC.get(key);
    }

    private static void replace(String key, String value) {
        if (value == null) {
            MDC.remove(key);
        } else {
            MDC.put(key, value);
        }
    }
}
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而後把這個類定義成Bean，這樣就能把它綁定到當前的tracer中去：

@Bean
public TracerBuilderCustomizer mdcBuilderCustomizer() {
		return builder -> builder.withScopeManager(new MDCScopeManager());
}
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而後利用%X{traceId}這種方式設置打印格式，啓動程序後就能在控制檯中看到輸出了：

是否是和spring-cloud-sleuth提供的方式同樣～～～

三、跨服務傳值

opentracing中提供了baggage元素來作跨進程的kv傳遞，咱們能夠利用baggage來傳遞咱們須要傳遞的值。（注意：同時他也會產生巨大的開銷，請當心使用此特性）

public class TraceContext {

    public static void setField(String key, String value) {
        if (GlobalTracer.isRegistered() && StringUtils.isNotBlank(key) && StringUtils.isNotBlank(value)) {
            Tracer tracer = GlobalTracer.get();
            tracer.activeSpan().setBaggageItem(key, value);
        }
    }

    public static String getFiled(String key, String defaultValue) {
        if (GlobalTracer.isRegistered() && StringUtils.isNotBlank(key)) {
            Tracer tracer = GlobalTracer.get();
            return tracer.activeSpan().getBaggageItem(key);
        }
        return defaultValue;
    }

}
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四、多線程中的trace

項目中須要依賴opentracing-concurrent：

<dependency>
    <groupId>io.opentracing.contrib</groupId>
    <artifactId>opentracing-concurrent</artifactId>
    <version>0.4.0</version>
</dependency>
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而後能夠經過TraceRunnable來建立帶有trace的線程

new Thread(new TracedRunnable(() -> {
	//線程中幹活....
	
}, GlobalTracer.get()));
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Spring環境中也能夠用@Autowired來獲取tracer

@Autowired
private Tracer tracer;
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