Spark Streaming---UpdatestateBykey(java)

package com.spark.streaming;import java.util.Arrays;import java.util.List;import org.apache.spark.SparkConf;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.streaming.Durations;import org.apache.spark.streaming.api.java.JavaDStream;import org.apache.spark.streaming.api.java.JavaPairDStream;import org.apache.spark.streaming.api.java.JavaReceiverInputDStream;import org.apache.spark.streaming.api.java.JavaStreamingContext;import com.google.common.base.Optional;import scala.Tuple2;public class UpdateStateByKeyWordcount {    public static void main(String[] args) {        SparkConf conf = new SparkConf().setAppName("UpdateStateByKeyWordcount").setMaster("local[2]");        JavaStreamingContext jssc = new JavaStreamingContext(conf , Durations.seconds(5));        jssc.checkpoint(".");        JavaReceiverInputDStream<String> lines = jssc.socketTextStream("node15", 8888);        JavaDStream<String> words = lines.flatMap(new FlatMapFunction<String, String>() {            private static final long serialVersionUID = 1L;            @Override            public Iterable<String> call(String line) throws Exception {                return Arrays.asList(line.split(" "));            }        });        JavaPairDStream<String, Integer> pairs = words.mapToPair(new PairFunction<String, String, Integer>() {            private static final long serialVersionUID = 1L;            @Override            public Tuple2<String, Integer> call(String word) throws Exception {                return new Tuple2<String, Integer>(word, 1);            }        });        JavaPairDStream<String, Integer> wordcounts = pairs.updateStateByKey(new Function2<List<Integer>, Optional<Integer>, Optional<Integer>>() {            private static final long serialVersionUID = 1L;            // 实际上,对于每个单词,每次batch计算的时候,都会调用这个函数,第一个参数values相当于这个batch中            // 这个key对应的新的一组值,可能有多个,可能2个1,(xuruyun,1)(xuruyun,1),那么这个values就是(1,1)            // 那么第二个参数表示的是这个key之前的状态,我们看类型Integer你也就知道了,这里是泛型咱们自己指定的            @Override            public Optional<Integer> call(List<Integer> values,                    Optional<Integer> state) throws Exception {                // Optional其实有两个子类,一个子类是Some,一个子类是None                // 就是key有可能之前从来都没有出现过,意味着之前从来没有更新过状态                Integer newValue = 0;                if(state.isPresent()){                    newValue = state.get();                }                for(Integer value : values){                    newValue += value;                }                return Optional.of(newValue);            }        });        wordcounts.print();        jssc.start();        jssc.awaitTermination();        jssc.stop();        jssc.close();    }}