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

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 D:\devtools\Java\jdk1..0_191\jre\lib\charsets.jar;D:\devtools\Java\jdk1..0_191\jre\lib\deploy.jar;D:\devtools\Java\jdk1..0_191\jre\lib\ext\access-bridge-.jar;D:\devtools\Java\jdk1..0_191\jre\lib\ext\cldrdata.jar;D:\devtools\Java\jdk1..0_191\jre\lib\ext\dnsns.jar;D:\devtools\Java\jdk1..0_191\jre\lib\ext\jaccess.jar;D:\devtools\Java\jdk1..0_191\jre\lib\ext\jfxrt.jar;D:\devtools\Java\jdk1..0_191\jre\lib\ext\localedata.jar;D:\devtools\Java\jdk1..0_191\jre\lib\ext\nashorn.jar;D:\devtools\Java\jdk1..0_191\jre\lib\ext\sunec.jar;D:\devtools\Java\jdk1..0_191\jre\lib\ext\sunjce_provider.jar;D:\devtools\Java\jdk1..0_191\jre\lib\ext\sunmscapi.jar;D:\devtools\Java\jdk1..0_191\jre\lib\ext\sunpkcs11.jar;D:\devtools\Java\jdk1..0_191\jre\lib\ext\zipfs.jar;D:\devtools\Java\jdk1..0_191\jre\lib\javaws.jar;D:\devtools\Java\jdk1..0_191\jre\lib\jce.jar;D:\devtools\Java\jdk1..0_191\jre\lib\jfr.jar;D:\devtools\Java\jdk1..0_191\jre\lib\jfxswt.jar;D:\devtools\Java\jdk1..0_191\jre\lib\jsse.jar;D:\devtools\Java\jdk1..0_191\jre\lib\management-agent.jar;D:\devtools\Java\jdk1..0_191\jre\lib\plugin.jar;D:\devtools\Java\jdk1..0_191\jre\lib\resources.jar;D:\devtools\Java\jdk1..0_191\jre\lib\rt.jar;D:\workspace\Spark_Test\target\classes;C:\Users\一期一会\.m2\repository\org\apache\spark\spark-core_2.\2.4.\spark-core_2.-2.4..jar;C:\Users\一期一会\.m2\repository\org\apache\avro\avro\1.8.\avro-1.8..jar;C:\Users\一期一会\.m2\repository\org\codehaus\jackson\jackson-core-asl\1.9.\jackson-core-asl-1.9..jar;C:\Users\一期一会\.m2\repository\org\codehaus\jackson\jackson-mapper-asl\1.9.\jackson-mapper-asl-1.9..jar;C:\Users\一期一会\.m2\repository\com\thoughtworks\paranamer\paranamer\2.7\paranamer-2.7.jar;C:\Users\一期一会\.m2\repository\org\apache\commons\commons-compress\1.8.\commons-compress-1.8..jar;C:\Users\一期一会\.m2\repository\org\tukaani\xz\1.5\xz-1.5.jar;C:\Users\一期一会\.m2\repository\org\apache\avro\avro-mapred\1.8.\avro-mapred-1.8.-hadoop2.jar;C:\Users\一期一会\.m2\repository\org\apache\avro\avro-ipc\1.8.\avro-ipc-1.8..jar;C:\Users\一期一会\.m2\repository\commons-codec\commons-codec\1.9\commons-codec-1.9.jar;C:\Users\一期一会\.m2\repository\com\twitter\chill_2.\0.9.\chill_2.-0.9..jar;C:\Users\一期一会\.m2\repository\com\esotericsoftware\kryo-shaded\4.0.\kryo-shaded-4.0..jar;C:\Users\一期一会\.m2\repository\com\esotericsoftware\minlog\1.3.\minlog-1.3..jar;C:\Users\一期一会\.m2\repository\org\objenesis\objenesis\2.5.\objenesis-2.5..jar;C:\Users\一期一会\.m2\repository\com\twitter\chill-java\0.9.\chill-java-0.9..jar;C:\Users\一期一会\.m2\repository\org\apache\xbean\xbean-asm6-shaded\4.8\xbean-asm6-shaded-4.8.jar;C:\Users\一期一会\.m2\repository\org\apache\hadoop\hadoop-client\2.6.\hadoop-client-2.6..jar;C:\Users\一期一会\.m2\repository\org\apache\hadoop\hadoop-common\2.6.\hadoop-common-2.6..jar;C:\Users\一期一会\.m2\repository\commons-cli\commons-cli\1.2\commons-cli-1.2.jar;C:\Users\一期一会\.m2\repository\xmlenc\xmlenc\0.52\xmlenc-0.52.jar;C:\Users\一期一会\.m2\repository\commons-httpclient\commons-httpclient\3.1\commons-httpclient-3.1.jar;C:\Users\一期一会\.m2\repository\commons-io\commons-io\2.4\commons-io-2.4.jar;C:\Users\一期一会\.m2\repository\commons-collections\commons-collections\3.2.\commons-collections-3.2..jar;C:\Users\一期一会\.m2\repository\commons-configuration\commons-configuration\1.6\commons-configuration-1.6.jar;C:\Users\一期一会\.m2\repository\commons-digester\commons-digester\1.8\commons-digester-1.8.jar;C:\Users\一期一会\.m2\repository\commons-beanutils\commons-beanutils\1.7.\commons-beanutils-1.7..jar;C:\Users\一期一会\.m2\repository\commons-beanutils\commons-beanutils-core\1.8.\commons-beanutils-core-1.8..jar;C:\Users\一期一会\.m2\repository\com\google\code\gson\gson\2.2.\gson-2.2..jar;C:\Users\一期一会\.m2\repository\org\apache\hadoop\hadoop-auth\2.6.\hadoop-auth-2.6..jar;C:\Users\一期一会\.m2\repository\org\apache\httpcomponents\httpclient\4.2.\httpclient-4.2..jar;C:\Users\一期一会\.m2\repository\org\apache\httpcomponents\httpcore\4.2.\httpcore-4.2..jar;C:\Users\一期一会\.m2\repository\org\apache\directory\server\apacheds-kerberos-codec\2.0.-M15\apacheds-kerberos-codec-2.0.-M15.jar;C:\Users\一期一会\.m2\repository\org\apache\directory\server\apacheds-i18n\2.0.-M15\apacheds-i18n-2.0.-M15.jar;C:\Users\一期一会\.m2\repository\org\apache\directory\api\api-asn1-api\1.0.-M20\api-asn1-api-1.0.-M20.jar;C:\Users\一期一会\.m2\repository\org\apache\directory\api\api-util\1.0.-M20\api-util-1.0.-M20.jar;C:\Users\一期一会\.m2\repository\org\apache\curator\curator-client\2.6.\curator-client-2.6..jar;C:\Users\一期一会\.m2\repository\org\htrace\htrace-core\3.0.\htrace-core-3.0..jar;C:\Users\一期一会\.m2\repository\org\apache\hadoop\hadoop-hdfs\2.6.\hadoop-hdfs-2.6..jar;C:\Users\一期一会\.m2\repository\org\mortbay\jetty\jetty-util\6.1.\jetty-util-6.1..jar;C:\Users\一期一会\.m2\repository\xerces\xercesImpl\2.9.\xercesImpl-2.9..jar;C:\Users\一期一会\.m2\repository\xml-apis\xml-apis\1.3.\xml-apis-1.3..jar;C:\Users\一期一会\.m2\repository\org\apache\hadoop\hadoop-mapreduce-client-app\2.6.\hadoop-mapreduce-client-app-2.6..jar;C:\Users\一期一会\.m2\repository\org\apache\hadoop\hadoop-mapreduce-client-common\2.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com.hikvision.learn.TestEmptyDataFrame

+---+----+---+-----+

| id|name|age|birth|

+---+----+---+-----+

+---+----+---+-----+

+---+----+---+-----+

| id|name|age|birth|

+---+----+---+-----+

+---+----+---+-----+

++

||

++

++

Process finished with exit code