public class KTableAggDemo {

    private static final Logger logger = LogManager.getLogger();

​

    public static void main(String[] args) {

        Properties props = new Properties();

        props.put(StreamsConfig.APPLICATION_ID_CONFIG, AppConfigs.applicationID);

        props.put(StreamsConfig.BOOTSTRAP_SERVERS_CONFIG, AppConfigs.bootstrapServers);

        props.put(StreamsConfig.STATE_DIR_CONFIG, AppConfigs.stateStoreLocation);

        props.put(StreamsConfig.COMMIT_INTERVAL_MS_CONFIG,100);

​

        StreamsBuilder streamsBuilder = new StreamsBuilder();

        streamsBuilder.table(AppConfigs.topicName,

            Consumed.with(AppSerdes.String(), AppSerdes.Employee()))

            .groupBy((k, v) -> KeyValue.pair(v.getDepartment(), v), Grouped.with(AppSerdes.String(), AppSerdes.Employee()))

            .aggregate(

                //Initializer

                () -> new DepartmentAggregate()

                    .withEmployeeCount(0)

                    .withTotalSalary(0)

                    .withAvgSalary(0D),

                //Adder

                (k, v, aggV) -> new DepartmentAggregate()

                    .withEmployeeCount(aggV.getEmployeeCount() + 1)

                    .withTotalSalary(aggV.getTotalSalary() + v.getSalary())

                    .withAvgSalary((aggV.getTotalSalary() + v.getSalary()) / (aggV.getEmployeeCount() + 1D)),

                //Subtractor

                (k, v, aggV) -> new DepartmentAggregate()

                    .withEmployeeCount(aggV.getEmployeeCount() - 1)

                    .withTotalSalary(aggV.getTotalSalary() - v.getSalary())

                    .withAvgSalary((aggV.getTotalSalary() - v.getSalary()) / (aggV.getEmployeeCount() - 1D)),

                //Serializer

                Materialized.<String, DepartmentAggregate, KeyValueStore<Bytes, byte[]>>as(

                    AppConfigs.stateStoreName).withValueSerde(AppSerdes.DepartmentAggregate())

            ).toStream().print(Printed.<String, DepartmentAggregate>toSysOut().withLabel("Department Aggregate"));

​

        KafkaStreams streams = new KafkaStreams(streamsBuilder.build(), props);

        streams.start();

​

        Runtime.getRuntime().addShutdownHook(new Thread(() -> {

            logger.info("Stopping Streams");

            streams.close();

        }));

    }

}

​