Sample AWS Kinesis Firehose lambda transformation in Java (Kotlin indeed)

FirehoseTransformer.kt

import com.amazonaws.services.lambda.runtime.Context
import com.amazonaws.services.lambda.runtime.LambdaLogger

class FirehoseTransformer {
    private lateinit var logger: LambdaLogger

    fun handler(event: KinesisFirehoseEvent, context: Context): KinesisFirehoseResponse {
        logger = context.getLogger()
        logger.log("Lambda started. Got messages ${event.records.size}.")

        val response = KinesisFirehoseResponse()
        for (rec in event.records) {

            val srcData = rec.decodedData()
            logger.log("Got message ${srcData}")

            //now deserialize you srcData from underlying format (e.g. JSON) and transform it to trgData
            val trgData = srcData

            val transformedRecord = KinesisFirehoseResponse.FirehoseRecord()
            transformedRecord.recordId = rec.recordId
            transformedRecord.result = KinesisFirehoseResponse.TRANSFORMED_STATE_OK
            transformedRecord.encodeAndSetData(trgData)

            response.records.add(transformedRecord)
        }
        return response
    }
}

KinesisFirehoseEvent.kt

import java.nio.charset.StandardCharsets
import java.util.*

/**
* This class represents the input event from Amazon Kinesis Firehose. It used as the input parameter
* for Lambda functions.
**/
class KinesisFirehoseEvent
{
    /**
    * The Id of the invocation.
    **/
    var invocationId : String = ""

    /**
    * The ARN of the delivery stream sending the event.
    **/
    var deliveryStreamArn = ""

    /**
    * The AWS region for delivery stream.
    **/
    var region = ""

    /**
    * The Kinesis records to transform.
    **/
    lateinit var records : List<FirehoseRecord>

    /**
    * The records for the Kinesis Firehose event to process and transform.
    **/
    public class FirehoseRecord
    {
        /**
        *The record ID is passed from Firehose to Lambda during the invocation. The transformed record must
        *contain the same record ID. Any mismatch between the ID of the original record and the ID of the
        *transformed record is treated as a data transformation failure.
        **/
        var recordId = ""


        /**
        * The approximate time the record was sent to Kinesis Firehose as a Unix epoch.
        **/
        var approximateArrivalEpoch : Long? = null

//        /**
//        * The approximate time the record was sent to Kinesis Firehose.
//        **/
//        [IgnoreDataMember]
//        public DateTime ApproximateArrivalTimestamp
//        {
//            get
//            {
//                var epoch = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);
//                return epoch.AddMilliseconds(ApproximateArrivalEpoch);
//            }
//        }

        /**
         * The data sent through as a Kinesis Firehose record. The data is sent to the Lambda function base64 encoded.
         **/
        var data : String? = null

        /**
         * Base64 decodes the data.
         **/
        fun decodedData() = String(Base64.getDecoder().decode(data), StandardCharsets.UTF_8);
    }
}

KinesisFirehoseResponse.kt

import java.nio.charset.StandardCharsets
import java.util.*

class KinesisFirehoseResponse {

    companion object {
        /**
         * The record was transformed successfully.
         **/
        val TRANSFORMED_STATE_OK = "Ok";

        /**
         * The record was dropped intentionally by your processing logic.
         **/
        val TRANSFORMED_STATE_DROPPED = "Dropped";

        /**
         * The record could not be transformed.
         **/
        val TRANSFORMED_STATE_PROCESSINGFAILED = "ProcessingFailed";
    }

    /**
    * The transformed records from the KinesisFirehoseEvent.
    **/
    var records = mutableListOf<FirehoseRecord>()

    /**
    * The transformed records after processing KinesisFirehoseEvent.Records
    **/
    public class FirehoseRecord
    {
        /**
        *The record ID is passed from Firehose to Lambda during the invocation. The transformed record must
        *contain the same record ID. Any mismatch between the ID of the original record and the ID of the
        *transformed record is treated as a data transformation failure.
        **/
        var recordId = ""

        /**
        * The status of the data transformation of the record. The possible values are: "Ok"
        * (the record was transformed successfully), "Dropped" (the record was dropped intentionally
        * by your processing logic), and "ProcessingFailed" (the record could not be transformed).
        * If a record has a status of "Ok" or "Dropped", Firehose considers it successfully
        * processed. Otherwise, Firehose considers it unsuccessfully processed.
        *
        * Possible values:
        * * Ok - The record was transformed successfully
        * * Dropped- The record was dropped intentionally by your processing logic
        * * ProcessingFailed - The record could not be transformed
        **/
        var result = TRANSFORMED_STATE_OK

        /**
        * The transformed data payload, after base64-encoding.
        **/
        var data : String? = null

        /**
        * Base64 encodes the unencodedData and sets the data property.
        **/
        fun encodeAndSetData(unencodedData: String)
        {
            data = Base64.getEncoder().encodeToString(unencodedData.toByteArray(StandardCharsets.UTF_8));
        }

        fun encodeAndSetData(unencodedData : ByteArray)
        {
            data = Base64.getEncoder().encodeToString(unencodedData);
        }
    }
}

Also the data field in KinesisFirehoseEvent is ByteBuffer but this post assumes it is encoded string, not sure how to handle this.

got it working... i dont need to decode when using KinesisFirehoseEvent