Why does from_json fail with “not found : value from_json”?

问题

I am reading a Kafka topic using Spark 2.1.1 (kafka 0.10+) and the payload is a JSON string. I'd like to parse the string with a schema and move forward with business logic.

Everyone seems to suggest that I should use from_json to parse the JSON strings, however, it doesn't seem to compile for my situation. The error being

not found : value from_json 
.select(from_json($"json", txnSchema) as "data")

When i tried the following lines into spark shell, it works just fine -

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

Any idea, what could I be doing wrong in the code to see this piece working in shell but not in IDE/compile time?

Here's the code:

import org.apache.spark.sql._

object Kafka10Cons3 extends App {
  val spark = SparkSession
    .builder
    .appName(Util.getProperty("AppName"))
    .master(Util.getProperty("spark.master"))
    .getOrCreate

  val stream = spark
    .readStream
    .format("kafka")
    .option("kafka.bootstrap.servers", Util.getProperty("kafka10.broker"))
    .option("subscribe", src_topic)
    .load

  val txnSchema = Util.getTxnStructure
  val df = stream
    .select($"value" cast "string" as "json")
    .select(from_json($"json", txnSchema) as "data")
    .select("data.*")
}

回答1:

you're probably just missing the relevant import - import org.apache.spark.sql.functions._.

You have imported spark.implicits._ and org.apache.spark.sql._, but none of these would import the individual function in functions.

---

I was also importing com.wizzardo.tools.json which looks like it also has a from_json function, which must have been the one the compiler chose (since it was imported first?) and which was apparently incompatible with my version of spark

Make sure you are not importing the from_json function from some other json library, as this library may be incompatible with the version of spark you are using.

来源：https://stackoverflow.com/questions/44077644/why-does-from-json-fail-with-not-found-value-from-json