Question: why use a UUID for Span ID

[IUSR]

java-span-reporter/span-reporter/src/main/java/io/opentracing/contrib/reporter/SpanBuilderR.java

Line 113 in 6e65e7f

String spanId = UUID.randomUUID().toString();

Is there a reason why a UUID is used? In the case of using Jaeger, I tested that all spans have hexadecimal IDs that can be parsed to 128-bit integers. Although the OpenTracing API doesn't require these IDs to be from numeric values, at least Jaeger is implemented in such away. When sending a span with a UUID span ID to Jaeger, I'm afraid it would complain about it, though I haven't been able to test this because all its client libraries demand a 128-bit integer.
If there's no strong reason, I'd suggest simply delegating to the wrapped span for span and trace Ids.

[NarimanAB]

I also think that in
private static final String BAGGAGE_SPANID_KEY = "reporter.spanId";
reporter.spanId must be reporter.spanid cause the default one is reporter.spanid.
with reporter.spanId the "baggage" contains two values with almost identical headers, but as I understand there must be only one with reporter.spanid key