为什么 from_json 失败并显示“未找到:值 from_json"? [英] Why does from_json fail with "not found : value from_json"?

问题描述

我正在使用 Spark 2.1.1 (kafka 0.10+) 阅读 Kafka 主题，有效负载是 JSON 字符串.我想用架构解析字符串并推进业务逻辑.

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.

似乎每个人都建议我应该使用 from_json 来解析 JSON 字符串，但是，它似乎不适合我的情况.错误是

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")

当我在 spark shell 中尝试以下几行时，它工作得很好 -

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.*")

任何想法，我在代码中做错了什么才能看到这部分在 shell 中运行但在 IDE/编译时不起作用?

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

代码如下:

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.*")
}

推荐答案

您可能只是缺少相关的导入 - import org.apache.spark.sql.functions._.

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

您已经导入了 spark.implicits._ 和 org.apache.spark.sql._，但是这些都不会导入 functions 中的单个函数.

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

我还导入了 com.wizzardo.tools.json 看起来它也有一个 from_json 函数，它一定是编译器选择的函数(因为它是先导入的?)，这显然与我的 spark 版本不兼容

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

确保您没有从其他 json 库中导入 from_json 函数，因为该库可能与您使用的 spark 版本不兼容.

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.

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