这是因为在BraveAutoConfiguration中，Tracing对象是用.traceId128Bit(true)构建的。
为了覆盖这个，我们必须在我们的应用程序中定义自定义Tracing bean，而不是依赖于Spring自动配置。
以下是Bean：

package com.example.trace;

import brave.Tracing;
import brave.TracingCustomizer;
import brave.handler.SpanHandler;
import brave.propagation.CurrentTraceContext;
import brave.propagation.Propagation;
import brave.sampler.Sampler;
import org.springframework.boot.actuate.autoconfigure.tracing.TracingProperties;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.env.Environment;

import java.util.List;

@Configuration
@EnableConfigurationProperties(TracingProperties.class)
public class BraveAutoConf {

    @Bean
    public Tracing braveTracing(Environment environment, TracingProperties properties, List<SpanHandler> spanHandlers,
                                List<TracingCustomizer> tracingCustomizers, CurrentTraceContext currentTraceContext,
                                Propagation.Factory propagationFactory, Sampler sampler) {

        //NOTE: skipped the type/produce/consume=W3C and span joining property compatibility check. (This is invalid config)

        String applicationName = environment.getProperty("spring.application.name", "AppName");
        Tracing.Builder builder = Tracing.newBuilder()
                .currentTraceContext(currentTraceContext)
                .traceId128Bit(false)
                .supportsJoin(properties.getBrave().isSpanJoiningSupported())
                .propagationFactory(propagationFactory)
                .sampler(sampler)
                .localServiceName(applicationName);
        spanHandlers.forEach(builder::addSpanHandler);
        for (TracingCustomizer tracingCustomizer : tracingCustomizers) {
            tracingCustomizer.customize(builder);
        }
        return builder.build();
    }

}

字符串
这将生成16个字符的traceId，而不是32个字符的trace+spanId。但是，请注意，traceId和第一个spanId将与此配置相同。