@java.lang.Override
  public void writeTo(com.google.protobuf.CodedOutputStream output) throws java.io.IOException {
    if (!com.google.protobuf.GeneratedMessageV3.isStringEmpty(projectId_)) {
      com.google.protobuf.GeneratedMessageV3.writeString(output, 1, projectId_);
    }
    if (!com.google.protobuf.GeneratedMessageV3.isStringEmpty(traceId_)) {
      com.google.protobuf.GeneratedMessageV3.writeString(output, 2, traceId_);
    }
    for (int i = 0; i < spans_.size(); i++) {
      output.writeMessage(3, spans_.get(i));
    }
    getUnknownFields().writeTo(output);
  }
<pre>
Collection of spans in the trace.
</pre>

<code>repeated .google.devtools.cloudtrace.v1.TraceSpan spans = 3;</code>
java-trace/proto-google-cloud-trace-v1/src/main/java/com/google/devtools/cloudtrace/v1/Trace.java