I have a Dataframe in Spark that looks like
eventDF
Sno|UserID|TypeExp
1|JAS123|MOVIE
2|ASP123|GAMES
3|JAS123|CLOTHING
4|DPS123|MOVIE
5|DPS123|CLOTHING
6|ASP123|MEDICAL
7|JAS123|OTH
8|POQ133|MEDICAL
.......
10000|DPS123|OTH
I need to write it to Kafka topic in Avro format currently i am able to write in Kafka as JSON using following code
val kafkaUserDF: DataFrame = eventDF.select(to_json(struct(eventDF.columns.map(column):_*)).alias("value"))
kafkaUserDF.selectExpr("CAST(value AS STRING)").write.format("kafka")
.option("kafka.bootstrap.servers", "Host:port")
.option("topic", "eventdf")
.save()
Now I want to write this in Avro format to Kafka topic
Spark >= 2.4:
You can use to_avro
function from spark-avro
library.
import org.apache.spark.sql.avro._
eventDF.select(
to_avro(struct(eventDF.columns.map(column):_*)).alias("value")
)
Spark < 2.4
You have to do it the same way:
Create a function which writes serialized Avro record to ByteArrayOutputStream
and return the result. A naive implementation (this supports only flat objects) could be similar to (adopted from Kafka Avro Scala Example by Sushil Kumar Singh)
import org.apache.spark.sql.Row
def encode(schema: org.apache.avro.Schema)(row: Row): Array[Byte] = {
val gr: GenericRecord = new GenericData.Record(schema)
row.schema.fieldNames.foreach(name => gr.put(name, row.getAs(name)))
val writer = new SpecificDatumWriter[GenericRecord](schema)
val out = new ByteArrayOutputStream()
val encoder: BinaryEncoder = EncoderFactory.get().binaryEncoder(out, null)
writer.write(gr, encoder)
encoder.flush()
out.close()
out.toByteArray()
}
Convert it to udf
:
import org.apache.spark.sql.functions.udf
val schema: org.apache.avro.Schema
val encodeUDF = udf(encode(schema) _)
Use it as drop in replacement for to_json
eventDF.select(
encodeUDF(struct(eventDF.columns.map(column):_*)).alias("value")
)