[英]How to use Scala Case Class to map Kafka source in Spark Structured Streaming
我正在嘗試在Spark中使用結構化流,因為它非常適合我的用例。 但是,我似乎找不到找到將來自Kafka的傳入數據映射到case類的方法。 根據官方文檔,這可以走多遠。
import sparkSession.sqlContext.implicits._
val kafkaDF:DataFrame = sparkSession
.readStream
.format("kafka")
.option("kafka.bootstrap.servers", bootstrapServers_CML)
.option("subscribe", topics_ME)
.option("startingOffsets", "latest")
.load()
.selectExpr("cast (value as string) as json") //Kakfa sends data in a specific schema (key, value, topic, offset, timestamp etc)
val schema_ME = StructType(Seq(
StructField("Parm1", StringType, true),
StructField("Parm2", StringType, true),
StructField("Parm3", TimestampType, true)))
val mobEventDF:DataFrame = kafkaDF
.select(from_json($"json", schema_ME).as("mobEvent")) //Using a StructType to convert to application specific schema. Cant seem to use a case class for schema directly yet. Perhaps with later API??
.na.drop()
mobEventDF具有這樣的模式
root
|-- appEvent: struct (nullable = true)
| |-- Parm1: string (nullable = true)
| |-- Parm2: string (nullable = true)
| |-- Parm3: string (nullable = true)
有一個更好的方法嗎? 我如何將其直接映射到Scala Case類(如下面的類)?
case class ME(name: String,
factory: String,
delay: Timestamp)
選擇並重命名所有字段,然后as
方法調用
kafkaDF.select($"mobEvent.*").toDF("name", "factory", "delay").as[ME]
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