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一、使用 Java API 和 JavaRDD 在 Spark SQL 中向数据帧添加新列

  在应用 mapPartition 函数后创建一个新的数据框：

import org.apache.spark.api.java.JavaRDD;
import org.apache.spark.api.java.function.FlatMapFunction;
import org.apache.spark.sql.Dataset;
import org.apache.spark.sql.Row;
import org.apache.spark.sql.RowFactory;
import org.apache.spark.sql.SparkSession;
import org.apache.spark.sql.types.DataTypes;
import org.apache.spark.sql.types.StructType;import java.io.IOException;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;public class Handler implements Serializable {public void handler(Dataset<Row> sourceData) {Dataset<Row> rowDataset = sourceData.where("rowKey = 'abcdefg_123'").selectExpr("split(rowKey, '_')[0] as id","name","time").where("name = '小强'").orderBy(functions.col("id").asc(), functions.col("time").desc());FlatMapFunction<Iterator<Row>,Row> mapPartitonstoTime = rows->{Int count = 0; // 只能在每个分区内自增，不能保证全局自增String startTime = "";String endTime = "";List<Row> mappedRows=new ArrayList<Row>();while(rows.hasNext()){count++;Row next = rows.next();String id = next.getAs("id");if (count == 2) {startTime = next.getAs("time");endTime = next.getAs("time");}Row mappedRow= RowFactory.create(next.getString(0), next.getString(1), next.getString(2), endTime, startTime);mappedRows.add(mappedRow);}return mappedRows.iterator();};JavaRDD<Row> sensorDataDoubleRDD=rowDataset.toJavaRDD().mapPartitions(mapPartitonstoTime);StructType oldSchema=rowDataset.schema();StructType newSchema =oldSchema.add("startTime",DataTypes.StringType,false).add("endTime",DataTypes.StringType,false);System.out.println("The new schema is: ");newSchema.printTreeString();System.out.println("The old schema is: ");oldSchema.printTreeString();Dataset<Row> sensorDataDoubleDF=spark.createDataFrame(sensorDataDoubleRDD, newSchema);sensorDataDoubleDF.show(100, false);}
}

打印结果：

The new schema is: 
root|-- id: string (nullable = true)|-- name: string (nullable = true)|-- time: string (nullable = true)The old schema is: 
root|-- id: string (nullable = true)|-- name: string (nullable = true)|-- time: string (nullable = true)|-- startTime: string (nullable = true)|-- endTime: string (nullable = true)+-----------+---------+----------+----------+----------+
|id         |name     |time      |startTime |endTime   |
+-----------+---------+----------+----------+----------+
|abcdefg_123|xiaoqiang|1693462023|1693462023|1693462023|
|abcdefg_321|xiaoliu  |1693462028|1693462028|1693462028|
+-----------+---------+----------+----------+----------+

参考：
java - 使用 Java API 和 JavaRDD 在 Spark SQL 中向数据帧添加新列
java.util.Arrays$ArrayList cannot be cast to java.util.Iterator

二、foreachPartition 遍历 Dataset

import org.apache.spark.api.java.JavaRDD;
import org.apache.spark.api.java.function.VoidFunction;
import org.apache.spark.sql.Dataset;
import org.apache.spark.sql.Row;
import org.apache.spark.sql.SparkSession;import java.io.IOException;
import java.io.Serializable;
import java.util.Iterator;public class Handler implements Serializable {public void handler(Dataset<Row> sourceData) {JavaRDD<Row> dataRDD = rowDataset.toJavaRDD();dataRDD.foreachPartition(new VoidFunction<Iterator<Row>>() {@Overridepublic void call(Iterator<Row> rowIterator) throws Exception {while (rowIterator.hasNext()) {Row next = rowIterator.next();String id = next.getAs("id");if (id.equals("123")) {String startTime = next.getAs("time");// 其他业务逻辑}}}});// 转换为 lambda 表达式dataRDD.foreachPartition((VoidFunction<Iterator<Row>>) rowIterator -> {while (rowIterator.hasNext()) {Row next = rowIterator.next();String id = next.getAs("id");if (id.equals("123")) {String startTime = next.getAs("time");// 其他业务逻辑}}});}
}

三、Dataset 自定义 Partitioner

参考：spark 自定义 partitioner 分区 java 版

import org.apache.commons.collections.CollectionUtils;
import org.apache.spark.Partitioner;
import org.junit.Assert;import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;/*** Created by lesly.lai on 2018/7/25.*/
public class CuxGroupPartitioner extends Partitioner {private int partitions;/*** map<key, partitionIndex>* 主要为了区分不同分区*/private Map<Object, Integer> hashCodePartitionIndexMap = new ConcurrentHashMap<>();public CuxGroupPartitioner(List<Object> groupList) {int size = groupList.size();this.partitions = size;initMap(partitions, groupList);}private void initMap(int size, List<Object> groupList) {Assert.assertTrue(CollectionUtils.isNotEmpty(groupList));for (int i=0; i<size; i++) {hashCodePartitionIndexMap.put(groupList.get(i), i);}}@Overridepublic int numPartitions() {return partitions;}@Overridepublic int getPartition(Object key) {return hashCodePartitionIndexMap.get(key);}public boolean equals(Object obj) {if (obj instanceof CuxGroupPartitioner) {return ((CuxGroupPartitioner) obj).partitions == partitions;}return false;}
}

查看分区分布情况工具类：
（1）Scala：

import org.apache.spark.sql.{Dataset, Row}/*** Created by lesly.lai on 2017/12FeeTask/25.*/
class SparkRddTaskInfo {def getTask(dataSet: Dataset[Row]) {val size = dataSet.rdd.partitions.lengthprintln(s"==> partition size: $size " )import scala.collection.Iteratorval showElements = (it: Iterator[Row]) => {val ns = it.toSeqimport org.apache.spark.TaskContextval pid = TaskContext.get.partitionIdprintln(s"[partition: $pid][size: ${ns.size}] ${ns.mkString(" ")}")}dataSet.foreachPartition(showElements)}
}

（2）Java：

import org.apache.spark.TaskContext;
import org.apache.spark.api.java.JavaRDD;
import org.apache.spark.api.java.function.VoidFunction;
import org.apache.spark.sql.Dataset;
import org.apache.spark.sql.Row;import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;public class SparkRddTaskInfo {public static void getTask(Dataset<Row> dataSet) {int size = dataSet.rdd().partitions().length;System.out.println("==> partition size:" + size);JavaRDD<Row> dataRDD = dataSet.toJavaRDD();dataRDD.foreachPartition((VoidFunction<Iterator<Row>>) rowIterator -> {List<String> mappedRows = new ArrayList<String>();int count = 0;while (rowIterator.hasNext()) {Row next = rowIterator.next();String id = next.getAs("id");String partitionKey = next.getAs("partition_key");String name = next.getAs("name");mappedRows.add(id + "/" + partitionKey+ "/" + name);}int pid = TaskContext.get().partitionId();System.out.println("[partition: " + pid + "][size: " + mappedRows.size() + "]" + mappedRows);});}
}

调用方式：

import com.vip.spark.db.ConnectionInfos;
import org.apache.spark.api.java.JavaPairRDD;
import org.apache.spark.api.java.JavaRDD;
import org.apache.spark.api.java.function.Function;
import org.apache.spark.sql.Column;
import org.apache.spark.sql.Dataset;
import org.apache.spark.sql.Row;
import org.apache.spark.sql.SparkSession;
import scala.Tuple2;import java.util.List;
import java.util.stream.Collectors;/*** Created by lesly.lai on 2018/7/23.*/
public class SparkSimpleTestPartition {public static void main(String[] args) throws InterruptedException {SparkSession sparkSession = SparkSession.builder().appName("Java Spark SQL basic example").getOrCreate();// 原始数据集Dataset<Row> originSet = sparkSession.read().jdbc(ConnectionInfos.TEST_MYSQL_CONNECTION_URL, "people", ConnectionInfos.getTestUserAndPasswordProperties());originSet.selectExpr("split(rowKey, '_')[0] as id","concat(split(rowKey, '_')[0],'_',split(rowKey, '_')[1]) as partition_key","split(rowKey, '_')[1] as name".createOrReplaceTempView("people");// 获取分区分布情况工具类SparkRddTaskInfo taskInfo = new SparkRddTaskInfo();Dataset<Row> groupSet = sparkSession.sql(" select partition_key from people group by partition_key");List<Object> groupList = groupSet.javaRDD().collect().stream().map(row -> row.getAs("partition_key")).collect(Collectors.toList());// 创建pairRDD 目前只有pairRdd支持自定义partitioner，所以需要先转成pairRddJavaPairRDD pairRDD = originSet.javaRDD().mapToPair(row -> {return new Tuple2(row.getAs("partition_key"), row);});// 指定自定义partitionerJavaRDD javaRdd = pairRDD.partitionBy(new CuxGroupPartitioner(groupList)).map(new Function<Tuple2<String, Row>, Row>(){@Overridepublic Row call(Tuple2<String, Row> v1) throws Exception {return v1._2;}});Dataset<Row> result = sparkSession.createDataFrame(javaRdd, originSet.schema());// 打印分区分布情况taskInfo.getTask(result);}
}

四、Dataset 重分区并且获取分区数

        System.out.println("1-->"+rowDataset.rdd().partitions().length);System.out.println("1-->"+rowDataset.rdd().getNumPartitions());Dataset<Row> hehe = rowDataset.coalesce(1);System.out.println("2-->"+hehe.rdd().partitions().length);System.out.println("2-->"+hehe.rdd().getNumPartitions());

运行结果：

1-->29
1-->29
2-->2
2-->2

注意：在使用 repartition() 时两次打印的结果相同：

print(rdd.getNumPartitions())
rdd.repartition(100)
print(rdd.getNumPartitions())

产生上述问题的原因有两个：
  首先 repartition() 是惰性求值操作，需要执行一个 action 操作才可以使其执行。
  其次，repartition() 操作会返回一个新的 rdd，并且新的 rdd 的分区已经修改为新的分区数，因此必须使用返回的 rdd，否则将仍在使用旧的分区。
  修改为：rdd2 = rdd.repartition(100)

参考：repartition() is not affecting RDD partition size