scala - 如何使用FileFormat格式的更新输出模式？

Question

我正在尝试在更新输出模式下使用 Spark 结构化流写入文件。我发现this StructuredSessionization example只要配置了控制台格式，它就可以正常工作。但如果我将输出模式更改为:

 val query = sessionUpdates
  .writeStream
  .outputMode("update")
  .format("json")
  .option("path", "/work/output/data")
  .option("checkpointLocation", "/work/output/checkpoint")
  .start()

我收到以下错误:

 Exception in thread "main" org.apache.spark.sql.AnalysisException: Data source json does not support Update output mode;
        at org.apache.spark.sql.execution.datasources.DataSource.createSink(DataSource.scala:279)
        at org.apache.spark.sql.streaming.DataStreamWriter.start(DataStreamWriter.scala:286)
        at palyground.StructuredStreamingMergeSpans$.main(StructuredStreamingMergeSpans.scala:84)
        at palyground.StructuredStreamingMergeSpans.main(StructuredStreamingMergeSpans.scala)

我可以使用更新模式并使用 FileFormat 将结果表写入文件接收器吗？在源代码中我发现了一个确保追加模式的模式匹配。

Answer 1

您无法使用 Spark 结构化流以更新模式写入文件。您需要为其编写ForeachWriter。我在这里为每个作家写了简单的内容。您可以根据您的要求进行修改。

val writerForText = new ForeachWriter[Row] {
    var fileWriter: FileWriter = _

    override def process(value: Row): Unit = {
      fileWriter.append(value.toSeq.mkString(","))
    }

    override def close(errorOrNull: Throwable): Unit = {
      fileWriter.close()
    }

    override def open(partitionId: Long, version: Long): Boolean = {
      FileUtils.forceMkdir(new File(s"src/test/resources/${partitionId}"))
      fileWriter = new FileWriter(new File(s"src/test/resources/${partitionId}/temp"))
      true

    }
  }

val query = sessionUpdates
  .writeStream
  .outputMode("update")
  .foreach(writerForText)
  .start()