@java.lang.Override
  public com.google.protobuf.ByteString getTraceIdBytes() {
    java.lang.Object ref = traceId_;
    if (ref instanceof java.lang.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