@Override
    public String toString() {
        String headers = this.headers == null ? "null" : this.headers.toString();
        String key = this.key == null ? "null" : this.key.toString();
        String value = this.value == null ? "null" : this.value.toString();
        String timestamp = this.timestamp == null ? "null" : this.timestamp.toString();
        return "ProducerRecord(topic=" + topic + ", partition=" + partition + ", headers=" + headers + ", key=" + key + ", value=" + value +
            ", timestamp=" + timestamp + ")";
    }
@return The partition to which the record will be sent (or null if no partition was specified)
clients/src/main/java/org/apache/kafka/clients/producer/ProducerRecord.java