java实现spark常用算子之mapPartitionsWithIndex

import org.apache.spark.SparkConf;
import org.apache.spark.api.java.JavaRDD;
import org.apache.spark.api.java.JavaSparkContext;
import org.apache.spark.api.java.function.Function2;
import org.apache.spark.api.java.function.VoidFunction;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.List;

/**
 * mapPartitionsWithIndex算子：
 * 与mapPartitions相似,可以看见使用到了哪一个partitions
 *
 * mapPartitions第二个参数preservesPartition(boolean,默认为false)的含义:
 *      此标志用于优化目的，当您不修改分区时，将它设置为false，
 *      如果您需要修改分区时，将它设置为true，这样spark可以更有效地执行操作，
 *      但如果您不告诉spark，它无法知道你的目的，也将无法达到优化的目的。
 *
 * 采用分区的话：parallelize优先级最高,其次是conf.set,最后是local[]
 */
public class MapPartitionsWithIndexOperator {

    public static void main(String[] args){
        SparkConf conf = new SparkConf().setMaster("local").setAppName("mapPartitionsWithIndex");
        JavaSparkContext sc = new JavaSparkContext(conf);

        List<String> names = Arrays.asList("w1","w2","w3","w4","w5","W6","W7");

        //将list转为RDD并且分为2个partition
        JavaRDD<String> nameRDD = sc.parallelize(names,2);

        // Function2入参：第一个参数为partition的index,第二个为入参，第三个为返回值
        JavaRDD<String> resultRDD = nameRDD.mapPartitionsWithIndex(new Function2<Integer, Iterator<String>, Iterator<String>>() {
            @Override
            public Iterator<String> call(Integer integer, Iterator<String> iterator) throws Exception {
                List<String> nameList = new ArrayList<>();
                while (iterator.hasNext()){
                    nameList.add(integer+":"+iterator.next());
                }
                return nameList.iterator();
            }
        },true);

        //修改sparkRDD分区
        JavaRDD<String> repartitionRDD = resultRDD.repartition(4);
        System.err.println(repartitionRDD.partitions().size());

        repartitionRDD.foreach(new VoidFunction<String>() {
            @Override
            public void call(String s) throws Exception {
                System.err.println("mapPartitionsWithIndex:"+s);
            }
        });

    }
}

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