How to use from_json with Kafka connect 0.10 and Spark Structured Streaming?

13
votes

I was trying to reproduce the example from [Databricks][1] and apply it to the new connector to Kafka and spark structured streaming however I cannot parse the JSON correctly using the out-of-the-box methods in Spark...

note: the topic is written into Kafka in JSON format.

val ds1 = spark
          .readStream
          .format("kafka")
          .option("kafka.bootstrap.servers", IP + ":9092")
          .option("zookeeper.connect", IP + ":2181")
          .option("subscribe", TOPIC)
          .option("startingOffsets", "earliest")
          .option("max.poll.records", 10)
          .option("failOnDataLoss", false)
          .load()

The following code won't work, I believe that's because the column json is a string and does not match the method from_json signature...

    val df = ds1.select($"value" cast "string" as "json")
                .select(from_json("json") as "data")
                .select("data.*")

Any tips?

[UPDATE] Example working: https://github.com/katsou55/kafka-spark-structured-streaming-example/blob/master/src/main/scala-2.11/Main.scala

1
scalaapache-sparkapache-kafkaapache-kafka-connectspark-structured-streaming

1 Answers

25
votes

First you need to define the schema for your JSON message. For example

val schema = new StructType()
  .add($"id".string)
  .add($"name".string)

Now you can use this schema in from_json method like below.

val df = ds1.select($"value" cast "string" as "json")
            .select(from_json($"json", schema) as "data")
            .select("data.*")