streams/examples/src/main/java/org/apache/kafka/streams/examples/wordcount/WordCountProcessorDemo.java

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
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package org.apache.kafka.streams.examples.wordcount;

import org.apache.kafka.clients.consumer.ConsumerConfig;
import org.apache.kafka.common.serialization.Serdes;
import org.apache.kafka.streams.KeyValue;
import org.apache.kafka.streams.StreamsConfig;
import org.apache.kafka.streams.KafkaStreams;
import org.apache.kafka.streams.processor.Processor;
import org.apache.kafka.streams.processor.ProcessorContext;
import org.apache.kafka.streams.processor.ProcessorSupplier;
import org.apache.kafka.streams.processor.TopologyBuilder;
import org.apache.kafka.streams.state.KeyValueIterator;
import org.apache.kafka.streams.state.KeyValueStore;
import org.apache.kafka.streams.state.Stores;

import java.util.Properties;

/**
 * Demonstrates, using the low-level Processor APIs, how to implement the WordCount program
 * that computes a simple word occurrence histogram from an input text.
 *
 * In this example, the input stream reads from a topic named "streams-file-input", where the values of messages
 * represent lines of text; and the histogram output is written to topic "streams-wordcount-processor-output" where each record
 * is an updated count of a single word.
 *
 * Before running this example you must create the source topic (e.g. via bin/kafka-topics.sh --create ...)
 * and write some data to it (e.g. via bin-kafka-console-producer.sh). Otherwise you won't see any data arriving in the output topic.
 */
public class WordCountProcessorDemo {

    private static class MyProcessorSupplier implements ProcessorSupplier<String, String> {

        @Override
        public Processor<String, String> get() {
            return new Processor<String, String>() {
                private ProcessorContext context;
                private KeyValueStore<String, Integer> kvStore;

                @Override
                @SuppressWarnings("unchecked")
                public void init(ProcessorContext context) {
                    this.context = context;
                    this.context.schedule(1000);
                    this.kvStore = (KeyValueStore<String, Integer>) context.getStateStore("Counts");
                }

                @Override
                public void process(String dummy, String line) {
                    String[] words = line.toLowerCase().split(" ");

                    for (String word : words) {
                        Integer oldValue = this.kvStore.get(word);

                        if (oldValue == null) {
                            this.kvStore.put(word, 1);
                        } else {
                            this.kvStore.put(word, oldValue + 1);
                        }
                    }

                    context.commit();
                }

                @Override
                public void punctuate(long timestamp) {
                    KeyValueIterator<String, Integer> iter = this.kvStore.all();

                    System.out.println("----------- " + timestamp + " ----------- ");

                    while (iter.hasNext()) {
                        KeyValue<String, Integer> entry = iter.next();

                        System.out.println("[" + entry.key + ", " + entry.value + "]");

                        context.forward(entry.key, entry.value.toString());
                    }

                    iter.close();
                }

                @Override
                public void close() {
                    this.kvStore.close();
                }
            };
        }
    }

    public static void main(String[] args) throws Exception {
        Properties props = new Properties();
        props.put(StreamsConfig.APPLICATION_ID_CONFIG, "streams-wordcount-processor");
        props.put(StreamsConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
        props.put(StreamsConfig.ZOOKEEPER_CONNECT_CONFIG, "localhost:2181");
        props.put(StreamsConfig.KEY_SERDE_CLASS_CONFIG, Serdes.String().getClass());
        props.put(StreamsConfig.VALUE_SERDE_CLASS_CONFIG, Serdes.String().getClass());

        // setting offset reset to earliest so that we can re-run the demo code with the same pre-loaded data
        props.put(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "earliest");

        TopologyBuilder builder = new TopologyBuilder();

        builder.addSource("Source", "streams-file-input");

        builder.addProcessor("Process", new MyProcessorSupplier(), "Source");
        builder.addStateStore(Stores.create("Counts").withStringKeys().withIntegerValues().inMemory().build(), "Process");

        builder.addSink("Sink", "streams-wordcount-processor-output", "Process");

        KafkaStreams streams = new KafkaStreams(builder, props);
        streams.start();

        // usually the stream application would be running forever,
        // in this example we just let it run for some time and stop since the input data is finite.
        Thread.sleep(5000L);

        streams.close();
    }
}