in kinesis-taxi-stream-producer/src/main/java/com/amazonaws/flink/refarch/events/WatermarkEvent.java [24:31]
public WatermarkEvent(long timestamp) {
super(
new ObjectNode(JsonNodeFactory.instance)
.put("watermark", new DateTime(timestamp).toString())
.put(TYPE_FIELD, "watermark")
.toString()
);
}