Spark Dataframe 转 Json

import org.apache.spark.sql.DataFrame
import org.apache.spark.sql.functions._
import org.apache.spark.sql.types._

// Convenience function for turning JSON strings into DataFrames.
def jsonToDataFrame(json: String, schema: StructType = null): DataFrame = {
  // SparkSessions are available with Spark 2.0+
  val reader = spark.read

  Option(schema).foreach(reader.schema)
  reader.json(sc.parallelize(Array(json)))
}

// Using a struct
val schema = new StructType().add("a", new StructType().add("b", IntegerType))
                          
val events = jsonToDataFrame("""
{
  "a": {
     "b": 1
  }
}
""", schema)

events.select("a.b").show()

val events = jsonToDataFrame("""
{
  "a": 1,
  "b": 2,
  "c": 3
}
""")

events.select(struct('a as 'y) as 'x).printSchema()
events.select(struct('a as 'y) as 'x).show()

val events = jsonToDataFrame("""
{
  "a": 1,
  "b": 2
}
""")

events.select((struct("*") as 'x)).show()

events.select(to_json(struct("*")) as 'x).show()

val df = Seq(("Rey", "23"), ("John", "44"),("Shuai", "20") ).toDF("key", "age")
df.columns.map(column)

val newdf = df.select(to_json(struct(df.columns.map(column):_*)).alias("value"))
newdf.show(false)

Ref:

https://docs.databricks.com/_static/notebooks/transform-complex-data-types-scala.html