public Builder setTraceId(java.lang.String value) {
      if (value == null) {
        throw new NullPointerException();
      }
      traceId_ = value;
      bitField0_ |= 0x00000002;
      onChanged();
      return this;
    }
<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>

@param value The traceId to set.
@return This builder for chaining.
java-trace/proto-google-cloud-trace-v1/src/main/java/com/google/devtools/cloudtrace/v1/Trace.java