BAEL-5582 add code for the kafka message filtering improvement

spring-kafka/src/main/java/com/baeldung/spring/kafka/Farewell.java

@@ -0,0 +1,37 @@
+package com.baeldung.spring.kafka;
+
+public class Farewell {
+
+    private String message;
+    private Integer remainingMinutes;
+
+    public Farewell() {
+    }
+
+    public Farewell(String message, Integer remainingMinutes) {
+        this.message = message;
+        this.remainingMinutes = remainingMinutes;
+    }
+
+    public String getMessage() {
+        return message;
+    }
+
+    public void setMessage(String message) {
+        this.message = message;
+    }
+
+    public Integer getRemainingMinutes() {
+        return remainingMinutes;
+    }
+
+    public void setRemainingMinutes(Integer remainingMinutes) {
+        this.remainingMinutes = remainingMinutes;
+    }
+
+    @Override
+    public String toString() {
+        return message + ". In " + remainingMinutes + "!";
+    }
+
+}

spring-kafka/src/main/java/com/baeldung/spring/kafka/KafkaApplicationMultiListener.java

@@ -0,0 +1,46 @@
+package com.baeldung.spring.kafka;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.context.ConfigurableApplicationContext;
+import org.springframework.context.annotation.Bean;
+import org.springframework.kafka.core.KafkaTemplate;
+
+@SpringBootApplication
+public class KafkaApplicationMultiListener {
+
+    public static void main(String[] args) throws Exception {
+
+        ConfigurableApplicationContext context = SpringApplication.run(KafkaApplicationMultiListener.class, args);
+
+        MessageProducer producer = context.getBean(MessageProducer.class);
+        producer.sendMessages();
+
+        Thread.sleep(5000);
+        context.close();
+    }
+
+    @Bean
+    public MessageProducer MessageProducer() {
+        return new MessageProducer();
+    }
+
+    public static class MessageProducer {
+
+        @Autowired
+        private KafkaTemplate<String, Object> multiTypeKafkaTemplate;
+
+        @Value(value = "${multi.type.topic.name}")
+        private String multiTypeTopicName;
+
+        public void sendMessages() {
+            multiTypeKafkaTemplate.send(multiTypeTopicName, new Greeting("Greetings", "World!"));
+            multiTypeKafkaTemplate.send(multiTypeTopicName, new Farewell("Farewell", 25));
+            multiTypeKafkaTemplate.send(multiTypeTopicName, "Simple string message");
+        }
+
+    }
+
+}

spring-kafka/src/main/java/com/baeldung/spring/kafka/KafkaConsumerConfig.java

@@ -12,6 +12,10 @@ import org.springframework.kafka.annotation.EnableKafka;
 import org.springframework.kafka.config.ConcurrentKafkaListenerContainerFactory;
 import org.springframework.kafka.core.ConsumerFactory;
 import org.springframework.kafka.core.DefaultKafkaConsumerFactory;
+import org.springframework.kafka.support.converter.RecordMessageConverter;
+import org.springframework.kafka.support.converter.StringJsonMessageConverter;
+import org.springframework.kafka.support.mapping.DefaultJackson2JavaTypeMapper;
+import org.springframework.kafka.support.mapping.Jackson2JavaTypeMapper;
 import org.springframework.kafka.support.serializer.JsonDeserializer;
 
 @EnableKafka
@@ -85,4 +89,35 @@ public class KafkaConsumerConfig {
         return factory;
     }
 
+    @Bean
+    public RecordMessageConverter multiTypeConverter() {
+        StringJsonMessageConverter converter = new StringJsonMessageConverter();
+        DefaultJackson2JavaTypeMapper typeMapper = new DefaultJackson2JavaTypeMapper();
+        typeMapper.setTypePrecedence(Jackson2JavaTypeMapper.TypePrecedence.TYPE_ID);
+        typeMapper.addTrustedPackages("com.baeldung.spring.kafka");
+        Map<String, Class<?>> mappings = new HashMap<>();
+        mappings.put("greeting", Greeting.class);
+        mappings.put("farewell", Farewell.class);
+        typeMapper.setIdClassMapping(mappings);
+        converter.setTypeMapper(typeMapper);
+        return converter;
+    }
+
+    @Bean
+    public ConsumerFactory<String, Object> multiTypeConsumerFactory() {
+        HashMap<String, Object> props = new HashMap<>();
+        props.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, bootstrapAddress);
+        props.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class);
+        props.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, JsonDeserializer.class);
+        return new DefaultKafkaConsumerFactory<>(props);
+    }
+
+    @Bean
+    public ConcurrentKafkaListenerContainerFactory<String, Object> multiTypeKafkaListenerContainerFactory() {
+        ConcurrentKafkaListenerContainerFactory<String, Object> factory = new ConcurrentKafkaListenerContainerFactory<>();
+        factory.setConsumerFactory(multiTypeConsumerFactory());
+        factory.setMessageConverter(multiTypeConverter());
+        return factory;
+    }
+
 }

spring-kafka/src/main/java/com/baeldung/spring/kafka/KafkaProducerConfig.java

@@ -1,5 +1,8 @@
 package com.baeldung.spring.kafka;
 
+import java.util.HashMap;
+import java.util.Map;
+
 import org.apache.kafka.clients.producer.ProducerConfig;
 import org.apache.kafka.common.serialization.StringSerializer;
 import org.springframework.beans.factory.annotation.Value;
@@ -10,9 +13,6 @@ import org.springframework.kafka.core.KafkaTemplate;
 import org.springframework.kafka.core.ProducerFactory;
 import org.springframework.kafka.support.serializer.JsonSerializer;
 
-import java.util.HashMap;
-import java.util.Map;
-
 @Configuration
 public class KafkaProducerConfig {
 
@@ -49,4 +49,19 @@ public class KafkaProducerConfig {
         return new KafkaTemplate<>(greetingProducerFactory());
     }
 
+    @Bean
+    public ProducerFactory<String, Object> multiTypeProducerFactory() {
+        Map<String, Object> configProps = new HashMap<>();
+        configProps.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, bootstrapAddress);
+        configProps.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
+        configProps.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, JsonSerializer.class);
+        configProps.put(JsonSerializer.TYPE_MAPPINGS, "greeting:com.baeldung.spring.kafka.Greeting, farewell:com.baeldung.spring.kafka.Farewell");
+        return new DefaultKafkaProducerFactory<>(configProps);
+    }
+
+    @Bean
+    public KafkaTemplate<String, Object> multiTypeKafkaTemplate() {
+        return new KafkaTemplate<>(multiTypeProducerFactory());
+    }
+
 }

spring-kafka/src/main/java/com/baeldung/spring/kafka/KafkaTopicConfig.java

@@ -31,6 +31,9 @@ public class KafkaTopicConfig {
     @Value(value = "${greeting.topic.name}")
     private String greetingTopicName;
 
+    @Value(value = "${multi.type.topic.name}")
+    private String multiTypeTopicName;
+
     @Bean
     public KafkaAdmin kafkaAdmin() {
         Map<String, Object> configs = new HashMap<>();
@@ -66,4 +69,9 @@ public class KafkaTopicConfig {
         newTopic.configs(configs);
         return newTopic;
     }
+
+    @Bean
+    public NewTopic multiTypeTopic() {
+        return new NewTopic(multiTypeTopicName, 1, (short) 1);
+    }
 }

spring-kafka/src/main/java/com/baeldung/spring/kafka/MultiTypeKafkaListener.java

@@ -0,0 +1,26 @@
+package com.baeldung.spring.kafka;
+
+import org.springframework.kafka.annotation.KafkaHandler;
+import org.springframework.kafka.annotation.KafkaListener;
+import org.springframework.stereotype.Component;
+
+@Component
+@KafkaListener(id = "multiGroup", topics = "multitype")
+public class MultiTypeKafkaListener {
+
+    @KafkaHandler
+    public void handleGreeting(Greeting greeting) {
+        System.out.println("Greeting received: " + greeting);
+    }
+
+    @KafkaHandler
+    public void handleF(Farewell farewell) {
+        System.out.println("Farewell received: " + farewell);
+    }
+
+    @KafkaHandler(isDefault = true)
+    public void unknown(Object object) {
+        System.out.println("Unkown type received: " + object);
+    }
+
+}

spring-kafka/src/main/resources/application.properties

@@ -4,14 +4,14 @@ long.message.topic.name=longMessage
 greeting.topic.name=greeting
 filtered.topic.name=filtered
 partitioned.topic.name=partitioned
-
+multi.type.topic.name=multitype
 # monitoring - lag analysis
 monitor.kafka.bootstrap.config=localhost:9092
 monitor.kafka.consumer.groupid=baeldungGrp
 monitor.topic.name=baeldung
-
 # monitoring - simulation
 monitor.producer.simulate=true
 monitor.consumer.simulate=true
 monitor.kafka.consumer.groupid.simulate=baeldungGrpSimulate
 test.topic=testtopic1
+