apache-flink Getting started with apache-flink WordCount


Example

Maven

Add the dependencies flink-java and flink-client (as explained in the JVM environment setup example).

The code

public class WordCount{

    public static void main( String[] args ) throws Exception{

        // set up the execution environment
        final ExecutionEnvironment env = ExecutionEnvironment.getExecutionEnvironment();

        // input data
        // you can also use env.readTextFile(...) to get words
        DataSet<String> text = env.fromElements(
                "To be, or not to be,--that is the question:--",
                "Whether 'tis nobler in the mind to suffer",
                "The slings and arrows of outrageous fortune",
                "Or to take arms against a sea of troubles,"
        );

        DataSet<Tuple2<String, Integer>> counts =
                // split up the lines in pairs (2-tuples) containing: (word,1)
                text.flatMap( new LineSplitter() )
                        // group by the tuple field "0" and sum up tuple field "1"
                        .groupBy( 0 )
                        .aggregate( Aggregations.SUM, 1 );

        // emit result
        counts.print();
    }   
}

LineSplitter.java:

public class LineSplitter implements FlatMapFunction<String, Tuple2<String, Integer>>{

    public void flatMap( String value, Collector<Tuple2<String, Integer>> out ){
        // normalize and split the line into words
        String[] tokens = value.toLowerCase().split( "\\W+" );

        // emit the pairs
        for( String token : tokens ){
            if( token.length() > 0 ){
                out.collect( new Tuple2<String, Integer>( token, 1 ) );
            }
        }
    }
}

If you use Java 8, you can replace .flatmap(new LineSplitter()) by a lambda expression:

DataSet<Tuple2<String, Integer>> counts = text
    // split up the lines in pairs (2-tuples) containing: (word,1)
    .flatMap( ( String value, Collector<Tuple2<String, Integer>> out ) -> {
        // normalize and split the line into words
        String[] tokens = value.toLowerCase().split( "\\W+" );

        // emit the pairs
        for( String token : tokens ){
            if( token.length() > 0 ){
                out.collect( new Tuple2<>( token, 1 ) );
            }
        }
    } )
    // group by the tuple field "0" and sum up tuple field "1"
    .groupBy( 0 )
    .aggregate( Aggregations.SUM, 1 );

Execution

From the IDE: simply hit run in your IDE. Flink will create an environment inside the JVM.

From the flink command line: to run the program using a standalone local environment, do the following:

  1. ensure flink is running (flink/bin/start-local.sh);

  2. create a jar file (maven package);

  3. use the flink command-line tool (in the bin folder of your flink installation) to launch the program:

    flink run -c your.package.WordCount target/your-jar.jar
    

    The -c option allows you to specify the class to run. It is not necessary if the jar is executable/defines a main class.

Result

(a,1)
(against,1)
(and,1)
(arms,1)
(arrows,1)
(be,2)
(fortune,1)
(in,1)
(is,1)
(mind,1)
(nobler,1)
(not,1)
(of,2)
(or,2)
(outrageous,1)
(question,1)
(sea,1)
(slings,1)
(suffer,1)
(take,1)
(that,1)
(the,3)
(tis,1)
(to,4)
(troubles,1)
(whether,1)