public com.google.protobuf.ByteString getTraceIdBytes() {
      java.lang.Object ref = traceId_;
      if (ref instanceof String) {
        com.google.protobuf.ByteString b =
            com.google.protobuf.ByteString.copyFromUtf8((java.lang.String) ref);
        traceId_ = b;
        return b;
      } else {
        return (com.google.protobuf.ByteString) ref;
      }
    }
<pre>
Globally unique identifier for the trace. This identifier is a 128-bit
numeric value formatted as a 32-byte hex string. For example,
`382d4f4c6b7bb2f4a972559d9085001d`.
</pre>

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

@return The bytes for traceId.
java-trace/proto-google-cloud-trace-v1/src/main/java/com/google/devtools/cloudtrace/v1/Trace.java