Kafka is most sought after event system today. In this series we will look at Kafka event messaging and streaming.
Github Repository link : https://github.com/CODINGSAINT/kafka-stream-spring
What will we be creating
We will create a streaming application using Spring and kafka streams.
We will have a continuously coming stream of famous quotes which will be continously produced at quote topic. Every quote can be tagged with multiple categories i.e. business,education,faith,famous-quotes,friendship,future,happiness,inspirational,life,love,nature,politics,proverb,religion,science,success,technology .
We will have topics related to each of the category. Once a quote comes we will be streaming them to respective category. To keep things simple for demo we have one listener listening to all of the topics
We have taken quotes from https://github.com/lukePeavey/quotable/blob/master/data/sample/quotes.json
These quotes will be streamed and will be sent to respective topic based on their category.
Listener will keep track of all the quotes which are streamed to these topics.
.
Installing kafka
### Download
To start kafka we require zookeeper , on kafka website we have different versions you can get the latest stable vesion from Kafka download page Say you have downloaded kafka_2.11-2.4.0.tgz
wget http://mirrors.estointernet.in/apache/kafka/2.4.0/kafka_2.11-2.4.0.tgz
Unzip
Use below command to unzip the downloaded file tar xzf kafka_2.11-2.4.0.tgz
### Move to user directory Move content to user directory
mv kafka_2.11-2.4.0/* /usr/local/kafka
### Run Zookeeper
Go to kafka directory and run
cd /usr/local/kafka bin/zookeeper-server-start.sh config/zookeeper.properties ### Run Kafka Server Use below command to run kafka server
bin/kafka-server-start.sh config/server.properties You will see logs confirming the kafka is up an running.
Test kafka installation
#### Create a topic
bin/kafka-topics.sh --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic kafka-test-topic
Verify if topic got created
bin/kafka-topics.sh --list --zookeeper localhost:2181 kafka-test-topic
#### Send messages to topic
Use below command to activate message terminal to kafka-test-topic. Below command will activate message sending to a topic , key in some interesting messages. Lets call it producer window
bin/kafka-console-producer.sh --broker-list localhost:9092 --topic kafka-test-topic >Welcome to Kafka
Consume the topic Open another terminal to consume messages
bin/kafka-console-consumer.sh --bootstrap-server localhost:9092 --topic kafka-test-topic --from-beginning
Now whatever you key in to producer window will be consumed to consumer window
Other ways to install kafka
There could be many other ways to install and run like using apt installer on Ubuntu , using a docker image etc. The above one is a generic setup .
Create Topics for for app
bin/kafka-topics.sh --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic quotes
bin/kafka-topics.sh --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic business
bin/kafka-topics.sh --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic education
bin/kafka-topics.sh --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic faith
bin/kafka-topics.sh --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic famous-quotes
bin/kafka-topics.sh --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic famous-quotes
bin/kafka-topics.sh --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic friendship
bin/kafka-topics.sh --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic future
bin/kafka-topics.sh --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic happiness
bin/kafka-topics.sh --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic inspirational
bin/kafka-topics.sh --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic life
bin/kafka-topics.sh --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic love
bin/kafka-topics.sh --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic nature
bin/kafka-topics.sh --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic politics
bin/kafka-topics.sh --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic proverb
bin/kafka-topics.sh --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic religion
bin/kafka-topics.sh --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic science
bin/kafka-topics.sh --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic success
bin/kafka-topics.sh --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic technology
Creating Spring Boot Kafka Stream project
We will create project using https://start.spring.io .
Go to website and dependencies
Download the project and open in your favourite IDE and open it.
Now we have Kafka installed up and running , as a First step we should be creating Quote bean which will flow the quotes from producer to consumer.
@Getter
@Setter
@ToString
public class Quote {
private String content;
private Set<String> tags;
private String author;
}
Let's add required configurations for Kafka. This includes Serializer and Deserializer
for Quotes.We have configurations for Spring Kafka template , producer and consumer.
Serialization and Deserialiation for key and value objects(POJO) have been mentioned seperately.
spring:
kafka:
listener:
missing-topics-fatal: false
client-id : quotes-app
bootstrap-server:
- localhost:9091
- localhost:9001
- localhost:9092
template:
default-topic: quotes
producer:
key-serializer: org.apache.kafka.common.serialization.StringSerializer
value-serializer: com.codingsaint.learning.kafkastreamspring.QuoteSerializer
consumer:
properties:
partition:
assignment:
strategy: org.apache.kafka.clients.consumer.RoundRobinAssignor
group-id: random-consumer
auto-offset-reset: earliest
key-deserializer: org.apache.kafka.common.serialization.StringDeserializer
value-deserializer: com.codingsaint.learning.kafkastreamspring.QuoteDeserializer
---
kafka:
topic:
input: quotes
output: business,education,faith,famous-quotes,friendship,future,happiness,inspirational,life,love,nature,politics,proverb,religion,science,success,technology
We will create QuoteSerializer , QuoteDeserializer and QuoteSerde which will have both serializer and deserializer
.We are using simple ObjectMapper to serialize and deserialize
QuoteSerializer
public class QuoteSerializer implements Serializer<Quote> {
@Override
public byte[] serialize(String s, Quote quote) {
byte[] retVal = null;
ObjectMapper objectMapper = new ObjectMapper();
try {
retVal = objectMapper.writeValueAsString(quote).getBytes();
} catch (Exception e) {
e.printStackTrace();
}
return retVal;
}
}
QuoteDeserializer
public class QuoteDeserializer implements Deserializer<Quote> {
@Override
public Quote deserialize(String s, byte[] bytes) {
ObjectMapper mapper = new ObjectMapper();
Quote quote = null;
try {
quote = mapper.readValue(bytes, Quote.class);
} catch (Exception e) {
e.printStackTrace();
}
return quote;
}
}
QuoteSerde
public class QuoteSerde implements Serde<Quote> {
public QuoteSerde() {
}
@Override
public Serializer<Quote> serializer() {
return new QuoteSerializer();
}
@Override
public Deserializer<Quote> deserializer() {
return new QuoteDeserializer();
}
}
Now Let us see the AppConfig class for configuring Producer and Consumer configurations.
@Configuration
@EnableKafka
@EnableKafkaStreams
public class AppConfig {
private static final Logger LOGGER= LoggerFactory.getLogger(AppConfig.class);
@Value("${kafka.topic.input}")
private String inputTopic;
@Value("#{'${kafka.topic.output}'.split(',')}")
private List<String> allTopics;
@Autowired
private KafkaProperties kafkaProperties;
/**
* Configurations for KafkaStreams
* @param kafkaProperties Will take defaults from application YAML or Properties file with spring.kafka
* @return kafkaConfiguration
*/
@Bean(name= KafkaStreamsDefaultConfiguration.DEFAULT_STREAMS_CONFIG_BEAN_NAME)
public KafkaStreamsConfiguration kafkaConfiguration(final KafkaProperties kafkaProperties){
Map<String, Object> config = new HashMap<>();
config.put(StreamsConfig.BOOTSTRAP_SERVERS_CONFIG, kafkaProperties.getBootstrapServers());
config.put(StreamsConfig.APPLICATION_ID_CONFIG, kafkaProperties.getClientId());
config.put(StreamsConfig.DEFAULT_KEY_SERDE_CLASS_CONFIG, Serdes.String().getClass());
config.put(StreamsConfig.DEFAULT_VALUE_SERDE_CLASS_CONFIG, QuoteSerde.class.getName() );
config.put(StreamsConfig.DEFAULT_DESERIALIZATION_EXCEPTION_HANDLER_CLASS_CONFIG, LogAndContinueExceptionHandler.class);
return new KafkaStreamsConfiguration(config);
}
/**
* The Stream which delegates each incoming topic to respective destination topic
* @param kStreamsBuilder
* @return
*/
@Bean
public KStream<String,Quote> kStream(StreamsBuilder kStreamsBuilder){
KStream<String,Quote> stream=kStreamsBuilder.stream(inputTopic);
for(String topic:allTopics){
stream.filter((s, quote) -> quote.getTags().contains(topic)).to(topic);
}
return stream;
}
/**
* Kafka ConsumerFactory configurations
* @return
*/
@Bean
public ConsumerFactory<String, Quote> consumerFactory() {
Map<String, Object> props = new HashMap<>();
props.put(
ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG,
kafkaProperties.getBootstrapServers());
props.put(
ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG,
StringDeserializer.class);
props.put(
ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG,
BytesDeserializer.class);
return new DefaultKafkaConsumerFactory<>(props);
}
/**
* Required Configuration for POJO to JSON
* @return ConcurrentKafkaListenerContainerFactory
*/
@Bean
public ConcurrentKafkaListenerContainerFactory<String, Quote>
kafkaListenerContainerFactory() {
ConcurrentKafkaListenerContainerFactory<String, Quote> factory =
new ConcurrentKafkaListenerContainerFactory<>();
factory.setConsumerFactory(consumerFactory());
factory.setMessageConverter(new StringJsonMessageConverter());
return factory;
}
}
- Since we have injected default KafkaProperties will have required bindings from application.yml .
- Beans for default Kafka Stream ,consumer factory and
ConcurrentKafkaListenerContainerFactoryis created whereConcurrentKafkaListenerContainerFactorybean help us to convert incoming message from String to Json usingStringJsonMessageConverter - KStream bean helps to create a stream on input topic (quotes) and filter based on tags. For each tag we already have created topics.
Now Let us look at Listener configuration which will listen all the topics
@Component
public class TopicConsumers {
private static final Logger LOGGER = LoggerFactory.getLogger(TopicConsumers.class);
@Value("#{'${kafka.topic.output}'.split(',')}")
private List<String> allTopics;
/**
* For simplicity we are listening all topics at one listener
*/
@KafkaListener(id = "allTopics", topics = "#{'${kafka.topic.output}'.split(',')}",
containerFactory = "kafkaListenerContainerFactory")
public void consume(@Payload Quote quote,
@Header(KafkaHeaders.RECEIVED_PARTITION_ID) int partition,
@Header(KafkaHeaders.RECEIVED_TOPIC) String incomingTopic,
@Header(KafkaHeaders.RECEIVED_TIMESTAMP) long ts
) {
LOGGER.info("Incoming quote {}-> {}", incomingTopic, quote);
}
}
- For simplicity we are listening all of these topics at one Listener
Once we run the application we will see logs confirming publishing of quotes with different tags and streams sending them to their respective category. Listener will listen incoming quotes.
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