In #105 davidB asks:
I would like to have read access to the Span id (SpanContext id) to be able to use it in log and in error reported (to end user,...). [skip] I need to expose the "trace id" in error message, then dev could use the trace to debug error reported by support, QA, end-user.
At the moment the OpenTracing API does not expose trace ID. It is being discussed in this issue: https://github.com/opentracing/specification/issues/24
One thing you can do right now is to call tracer.inject(null, Builtin.HTTP_HEADERS, map. It will put all IDs with baggage (SpanContext) into the map. Then you can get ID by its name. However this solution is not vedor neutral.
Other solution is to cast SpanContext into specific implementation and get the IDs by getter (if there is any)
Ben has offered a new way to provide this id. ref: https://github.com/opentracing/specification/issues/24#issuecomment-286261320
来源：https://stackoverflow.com/questions/42699603/how-can-i-get-a-trace-id-from-opentracing-api