import org.apache.spark.SparkConf;
import org.apache.spark.api.java.JavaPairRDD;
import org.apache.spark.api.java.JavaRDD;
import org.apache.spark.api.java.JavaSparkContext;
import org.apache.spark.api.java.function.FlatMapFunction;
import org.apache.spark.api.java.function.Function2;
import org.apache.spark.api.java.function.PairFunction;
import org.apache.spark.api.java.function.VoidFunction;
import scala.Tuple2;

import java.util.Arrays;
import java.util.Iterator;

/**
 * @Author yqq
 * @Date 2021/12/06 23:16
 * @Version 1.0
 */

/**
 * SparkScala api 与Java api 不同：
 * 1).java中需要创建 JavaSparkContext
 * 2).scala中是RDD ，java中是JavaRDD
 * 3).scala中将RDD转换成K,V格式的数据直接使用 map转出tuple数据即可
 *    Java中将RDD转换成K,V格式的数据需要使用mapToPair,转出K,V格式的数据
 *
 * 4).JavaPairRDD 在java中代表的是K,V格式的RDD
 *
 */
public class WordCountByJava {
    public static void main(String[] args) {
        SparkConf conf = new SparkConf();
        conf.setMaster("local");
        conf.setAppName("word_count_java");

        JavaSparkContext context = new JavaSparkContext(conf);
        JavaRDD<String> lines = context.textFile("data/words");
        JavaRDD<String> words = lines.flatMap(new FlatMapFunction<String, String>() {
            @Override
            public Iterator<String> call(String s) throws Exception {
                return Arrays.asList(s.split(" ")).iterator();
            }
        });
        JavaPairRDD<String, Integer> pairRDD = words.mapToPair(new PairFunction<String, String, Integer>() {
            @Override
            public Tuple2<String, Integer> call(String s) throws Exception {
                return new Tuple2<>(s, 1);
            }
        });
        JavaPairRDD<String, Integer> result = pairRDD.reduceByKey(new Function2<Integer, Integer, Integer>() {
            @Override
            public Integer call(Integer integer, Integer integer2) throws Exception {
                return integer + integer2;
            }
        });
        result.foreach(new VoidFunction<Tuple2<String, Integer>>() {
            @Override
            public void call(Tuple2<String, Integer> tuple2) throws Exception {
                System.out.println(tuple2);
            }
        });
    }
}

。。。。。很明显Java写的很复杂。。。。。。还是Scala真香