Spark Dataset mapGroups操作后的值类型为二进制，甚至在函数中返回String

Question

环境：

Spark version: 2.3.0
Run Mode: Local
Java version: Java 8

Spark应用程序尝试执行以下操作

1）将输入数据转换为数据集[GenericRecord]

2）按GenericRecord的关键属性分组>

3）在组后使用mapGroups迭代值列表并以String格式获得一些结果

4）在文本文件中将结果输出为字符串。

写入文本文件时发生错误。 Spark推断，在步骤3中生成的数据集具有一个二进制列，而不是一个String列。但实际上，它在mapGroups函数中返回一个String。

是否可以进行列数据类型转换，或者让Spark知道它实际上是字符串列而不是二进制列？

    val dslSourcePath = args(0)
    val filePath = args(1)
    val targetPath = args(2)
    val df = spark.read.textFile(filePath)

    implicit def kryoEncoder[A](implicit ct: ClassTag[A]): Encoder[A] = Encoders.kryo[A](ct)

    val mapResult = df.flatMap(abc => {
      JavaConversions.asScalaBuffer(some how return a list of Avro GenericRecord using a java library).seq;
    })

    val groupResult = mapResult.groupByKey(result => String.valueOf(result.get("key")))
      .mapGroups((key, valueList) => {
        val result = StringBuilder.newBuilder.append(key).append(",").append(valueList.count(_=>true))
        result.toString()
      })

    groupResult.printSchema()

    groupResult.write.text(targetPath + "-result-" + System.currentTimeMillis())


输出显示它是一个垃圾箱

root
 |-- value: binary (nullable = true)

Spark发出了一个错误，它不能将二进制形式写为文本：

Exception in thread "main" org.apache.spark.sql.AnalysisException: Text data source supports only a string column, but you have binary.;
    at org.apache.spark.sql.execution.datasources.text.TextFileFormat.verifySchema(TextFileFormat.scala:55)
    at org.apache.spark.sql.execution.datasources.text.TextFileFormat.prepareWrite(TextFileFormat.scala:78)
    at org.apache.spark.sql.execution.datasources.FileFormatWriter$.write(FileFormatWriter.scala:140)
    at org.apache.spark.sql.execution.datasources.InsertIntoHadoopFsRelationCommand.run(InsertIntoHadoopFsRelationCommand.scala:154)
    at org.apache.spark.sql.execution.command.DataWritingCommandExec.sideEffectResult$lzycompute(commands.scala:104)
    at org.apache.spark.sql.execution.command.DataWritingCommandExec.sideEffectResult(commands.scala:102)
    at org.apache.spark.sql.execution.command.DataWritingCommandExec.doExecute(commands.scala:122)
    at org.apache.spark.sql.execution.SparkPlan$$anonfun$execute$1.apply(SparkPlan.scala:131)
    at org.apache.spark.sql.execution.SparkPlan$$anonfun$execute$1.apply(SparkPlan.scala:127)
    at org.apache.spark.sql.execution.SparkPlan$$anonfun$executeQuery$1.apply(SparkPlan.scala:155)
    at org.apache.spark.rdd.RDDOperationScope$.withScope(RDDOperationScope.scala:151)
    at org.apache.spark.sql.execution.SparkPlan.executeQuery(SparkPlan.scala:152)
    at org.apache.spark.sql.execution.SparkPlan.execute(SparkPlan.scala:127)
    at org.apache.spark.sql.execution.QueryExecution.toRdd$lzycompute(QueryExecution.scala:80)
    at org.apache.spark.sql.execution.QueryExecution.toRdd(QueryExecution.scala:80)
    at org.apache.spark.sql.DataFrameWriter$$anonfun$runCommand$1.apply(DataFrameWriter.scala:654)
    at org.apache.spark.sql.DataFrameWriter$$anonfun$runCommand$1.apply(DataFrameWriter.scala:654)
    at org.apache.spark.sql.execution.SQLExecution$.withNewExecutionId(SQLExecution.scala:77)
    at org.apache.spark.sql.DataFrameWriter.runCommand(DataFrameWriter.scala:654)
    at org.apache.spark.sql.DataFrameWriter.saveToV1Source(DataFrameWriter.scala:273)
    at org.apache.spark.sql.DataFrameWriter.save(DataFrameWriter.scala:267)
    at org.apache.spark.sql.DataFrameWriter.save(DataFrameWriter.scala:225)
    at org.apache.spark.sql.DataFrameWriter.text(DataFrameWriter.scala:595)

环境：Spark版本：2.3.0运行模式：本地Java版本：Java 8 spark应用程序尝试执行以下操作1）将输入数据转换为数据集[GenericRecord] 2）通过键进行分组...

Answer 1

正如@ user10938362所说，原因是以下代码会将所有数据编码为字节

implicit def kryoEncoder[A](implicit ct: ClassTag[A]): Encoder[A] = Encoders.kryo[A](ct)