基于HDFS文件的实时计算,其实就是,监控一个HDFS目录,只要其中有新文件出现,就实时处理。相当于处理实时的文件流。
Spark Streaming会监视指定的HDFS目录,并且处理出现在目录中的文件。要注意的是,所有放入HDFS目录中的文件,都必须有相同的格式;必须使用移动或者重命名的方式,将文件移入目录;一旦处理之后,文件的内容即使改变,也不会再处理了;基于HDFS文件的数据源是没有Receiver的,因此不会占用一个cpu core。
WordCount
package cn.spark.streaming;
import java.util.Arrays;
import java.util.Iterator;
import org.apache.spark.SparkConf;
import org.apache.spark.api.java.JavaPairRDD;
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 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.JavaStreamingContext;
import scala.Tuple2;
/**
* 基于HDFS的 spark streaming 的 wordcount 程序
*
*/
public class HDFSWordCount {
public static void main(String[] args) throws Exception {
SparkConf conf = new SparkConf().setAppName("HDFSWordCount");
JavaStreamingContext jssc = new JavaStreamingContext(conf, Durations.seconds(5));
JavaDStream<String> lineDStream = jssc.textFileStream(args[0]);
// flatMap
JavaDStream<String> wordDStream = lineDStream.flatMap(
new FlatMapFunction<String, String>() {
private static final long serialVersionUID = -7716791306222529945L;
@Override
public Iterator<String> call(String line) throws Exception {
return Arrays.asList(line.split(" ")).iterator();
}
});
// mapToPair
JavaPairDStream<String, Integer> pairDStream = wordDStream.mapToPair(
new PairFunction<String, String, Integer>() {
private static final long serialVersionUID = 859183755407567155L;
@Override
public Tuple2<String, Integer> call(String word) throws Exception {
return new Tuple2<String, Integer>(word, 1);
}
});
// reduceByKey
JavaPairDStream<String, Integer> resultDStream = pairDStream.reduceByKey(
new Function2<Integer, Integer, Integer>() {
private static final long serialVersionUID = 6470112788289414159L;
@Override
public Integer call(Integer v1, Integer v2) throws Exception {
return v1 + v2;
}
});
resultDStream.print(100);
jssc.start();
jssc.awaitTermination();
jssc.close();
}
}
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