@java.lang.Override
    public com.google.protobuf.ByteString getSpanIdBytes() {
      java.lang.Object ref = spanId_;
      if (ref instanceof java.lang.String) {
        com.google.protobuf.ByteString b =
            com.google.protobuf.ByteString.copyFromUtf8((java.lang.String) ref);
        spanId_ = b;
        return b;
      } else {
        return (com.google.protobuf.ByteString) ref;
      }
    }
<pre>
The `[SPAN_ID]` for a span within a trace.
</pre>

<code>string span_id = 2;</code>

@return The bytes for spanId.
java-trace/proto-google-cloud-trace-v2/src/main/java/com/google/devtools/cloudtrace/v2/Span.java