title: How to use TraceContext to set a traceId in Spring Sleuth and brave?
body: <p>I need to set the traceId with an existing Id (we have created some kind of correlation-id from the main origin app) into brave tracer. </p>
  
  <p>I don't want to use the Spring Sleuth/brave created one as  I want to make it consistent throughout my different micro-services. I am able to create traces and span and able to send all details into Zipkin. My sample snippet:</p>
  
  <pre><code>import brave.Span;
  import brave.Span.Kind;
  import brave.Tracer;
  import brave.propagation.TraceContext;  
  
  span = this.tracer.nextSpan().name("myservice");
  span.kind(Kind.SERVER);
  span.tag("path", servletPath).start();
  </code></pre>
  
  <p>I am using: Spring Cloud 'Greenwich.BUILD-SNAPSHOT' and brave. The whole purpose is to search using correlationId rather than traceId in zipkin ui.</p>