ProcessorAPIExample.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;

import kafka.Kafka;
import org.apache.kafka.common.serialization.Serdes;
import org.apache.kafka.streams.processor.AbstractProcessor;
import org.apache.kafka.streams.processor.To;

import java.util.Properties;

public class ProcessorAPIExample {

    public static void main(String[] args) {

        final Properties properties = new Properties();
        properties.setProperty(StreamsConfig.APPLICATION_ID_CONFIG, "test-application");
        properties.setProperty(StreamsConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
        properties.setProperty(StreamsConfig.DEFAULT_KEY_SERDE_CLASS_CONFIG, Serdes.String().getClass().getName());
        properties.setProperty(StreamsConfig.DEFAULT_VALUE_SERDE_CLASS_CONFIG, Serdes.String().getClass().getName());


        final Topology topology = new Topology();

        topology.addSource("SourceTopicProcessor","input" );
        topology.addProcessor("FilteringProcessor", FilterProcessor::new, "SourceTopicProcessor");
        topology.addProcessor("MappingProcessor", MapValuesProcessor::new, "FilteringProcessor");
        topology.addSink("SinkProcessor", "output", "MappingProcessor");

        System.out.println(builder.describe());
        final KafkaStreams streams = new KafkaStreams(builder, properties);
        streams.start();
    }


    static class FilterProcessor extends AbstractProcessor<String, String> {
        @Override
        public void process(String key, String value) {
            if (value.endsWith("FOO")) {
                context().forward(key, value);
            }
        }
    }

    static class MapValuesProcessor extends AbstractProcessor<String, String> {

        @Override
        public void process(String key, String value) {
             context().forward(key, value.substring(0,3));
             // Processor API gives flexibility to forward KV pairs
             // to arbitrary child nodes
             //context().forward(key, value.substring(0,3), To.child("some node"));
        }
    }


}

Is this a working example ?
builder variable is not properly constructed before lines 45-46

System.out.println(topology.describe());
final KafkaStreams streams = new KafkaStreams(topology, properties);