Spark创建空的DataFrame

前言

本文主要给出Spark创建空的DataFrame的代码示例，这里讲的空的DataFrame主要指有列名（可以自己随意指定），但是没有行的DataFrame，因为自己在开发过程中有这个需求，之前并不知道怎么创建，就查了一下，发现资料并不多，不知道因为太简单还是用的人少_{，至于具体什么需求就不阐述了，主要给有这方面需求的小伙伴参考一下。还有另一种空的DataFrame就是没有任何行任何列的DataFrame，不知道有什么用，反正贴在代码里，万一有人用呢}

1、代码

代码较简单，如下

import org.apache.spark.sql.SparkSession
import org.apache.spark.sql.types._
import org.apache.spark.sql.Row
import org.apache.spark.rdd.EmptyRDD

/**
 * Spark创建空DataFrame示例
 */
object EmptyDataFrame {

  def main(args: Array[String]): Unit = {

    val spark = SparkSession.builder().appName("EmptyDataFrame").master("local").getOrCreate()

    /**
     * 创建一个空的DataFrame，代表用户
     * 有四列，分别代表ID、名字、年龄、生日
     */
    val colNames = Array("id", "name", "age", "birth")
    //为了简单起见，字段类型都为String
    val schema = StructType(colNames.map(fieldName => StructField(fieldName, StringType, true)))
    //主要是利用了spark.sparkContext.emptyRDD
    val emptyDf = spark.createDataFrame(spark.sparkContext.emptyRDD[Row], schema)

    emptyDf.show

    /**
     * 也可以给每列指定相对应的类型
     */
    val schema1 = StructType(
      Seq(
        StructField("id", IntegerType, true),
        StructField("name", StringType, true),
        StructField("age", IntegerType, true),
        StructField("birth", StringType, true)))
    val emptyDf1 = spark.createDataFrame(spark.sparkContext.emptyRDD[Row], schema1)
    emptyDf1.show

    //还有一种空的DataFrame，没有任何行任何列
    spark.emptyDataFrame.show

    spark.stop()
  }

}

2、结果

D:\devtools\Java\jdk1..0_191\bin\java.exe "-javaagent:D:\devtools\IntelliJ IDEA Community Edition 2018.2.6\lib\idea_rt.jar=64870:D:\devtools\IntelliJ IDEA Community Edition 2018.2.6\bin" -Dfile.encoding=UTF- -classpath 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com.hikvision.learn.TestEmptyDataFrame
+---+----+---+-----+
| id|name|age|birth|
+---+----+---+-----+
+---+----+---+-----+

+---+----+---+-----+
| id|name|age|birth|
+---+----+---+-----+
+---+----+---+-----+

++
||
++
++

Process finished with exit code