如何将 from_json 与 Kafka connect 0.10 和 Spark Structured Streaming 一起使用? [英] How to use from_json with Kafka connect 0.10 and Spark Structured Streaming?

问题描述

我试图从 [Databricks][1] 复制示例并将其应用到 Kafka 的新连接器并激发结构化流，但是我无法使用 Spark 中的开箱即用方法正确解析 JSON...

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...

注意:主题以JSON格式写入Kafka.

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()

下面的代码不行，我相信是因为json列是字符串，与方法from_json签名不匹配...

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.*")

有什么建议吗?

[更新] 工作示例:https://github.com/katsou55/kafka-spark-structured-streaming-example/blob/master/src/main/scala-2.11/Main.scala

推荐答案

首先，您需要为 JSON 消息定义架构.例如

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

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

现在您可以在 from_json 方法中使用此架构，如下所示.

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.*")

这篇关于如何将 from_json 与 Kafka connect 0.10 和 Spark Structured Streaming 一起使用?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！