BAEL-578: Add spring-kafka module (#1407)

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

@@ -0,0 +1,72 @@
+package com.baeldung.spring.kafka;
+
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+
+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.annotation.KafkaListener;
+import org.springframework.kafka.core.KafkaTemplate;
+
+@SpringBootApplication
+public class KafkaApplication {
+
+    public static void main(String[] args) throws Exception {
+        ConfigurableApplicationContext context = SpringApplication.run(KafkaApplication.class, args);
+        MessageProducer producer = context.getBean(MessageProducer.class);
+        producer.sendMessage("Hello, World!");
+
+        MessageListener listener = context.getBean(MessageListener.class);
+        listener.latch.await(20, TimeUnit.SECONDS);
+        Thread.sleep(60000);
+        context.close();
+
+    }
+
+    @Bean
+    public MessageProducer messageProducer() {
+        return new MessageProducer();
+    }
+
+    @Bean
+    public MessageListener messageListener() {
+        return new MessageListener();
+    }
+
+    public static class MessageProducer {
+
+        @Autowired
+        private KafkaTemplate<String, String> kafkaTemplate;
+
+        @Value(value = "${message.topic.name}")
+        private String topicName;
+
+        public void sendMessage(String message) {
+            kafkaTemplate.send(topicName, message);
+        }
+
+    }
+
+    public static class MessageListener {
+
+        private CountDownLatch latch = new CountDownLatch(2);
+
+        @KafkaListener(topics = "${message.topic.name}", group = "foo", containerFactory = "fooKafkaListenerContainerFactory")
+        public void listenGroupFoo(String message) {
+            System.out.println("Received Messasge in group 'foo': " + message);
+            latch.countDown();
+        }
+
+        @KafkaListener(topics = "${message.topic.name}", group = "bar", containerFactory = "barKafkaListenerContainerFactory")
+        public void listenGroupBar(String message) {
+            System.out.println("Received Messasge in group 'bar': " + message);
+            latch.countDown();
+        }
+
+    }
+
+}

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

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+package com.baeldung.spring.kafka;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import org.apache.kafka.clients.consumer.ConsumerConfig;
+import org.apache.kafka.common.serialization.StringDeserializer;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.kafka.annotation.EnableKafka;
+import org.springframework.kafka.config.ConcurrentKafkaListenerContainerFactory;
+import org.springframework.kafka.core.ConsumerFactory;
+import org.springframework.kafka.core.DefaultKafkaConsumerFactory;
+
+@EnableKafka
+@Configuration
+public class KafkaConsumerConfig {
+
+    @Value(value = "${kafka.bootstrapAddress}")
+    private String bootstrapAddress;
+
+    public ConsumerFactory<String, String> consumerFactory(String groupId) {
+        Map<String, Object> props = new HashMap<>();
+        props.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, bootstrapAddress);
+        props.put(ConsumerConfig.GROUP_ID_CONFIG, groupId);
+        props.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class);
+        props.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class);
+        return new DefaultKafkaConsumerFactory<>(props);
+    }
+
+    @Bean
+    public ConcurrentKafkaListenerContainerFactory<String, String> fooKafkaListenerContainerFactory() {
+        ConcurrentKafkaListenerContainerFactory<String, String> factory = new ConcurrentKafkaListenerContainerFactory<>();
+        factory.setConsumerFactory(consumerFactory("foo"));
+        return factory;
+    }
+    
+    @Bean
+    public ConcurrentKafkaListenerContainerFactory<String, String> barKafkaListenerContainerFactory() {
+        ConcurrentKafkaListenerContainerFactory<String, String> factory = new ConcurrentKafkaListenerContainerFactory<>();
+        factory.setConsumerFactory(consumerFactory("bar"));
+        return factory;
+    }
+}

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

@@ -0,0 +1,36 @@
+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;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.kafka.core.DefaultKafkaProducerFactory;
+import org.springframework.kafka.core.KafkaTemplate;
+import org.springframework.kafka.core.ProducerFactory;
+
+@Configuration
+public class KafkaProducerConfig {
+
+    @Value(value = "${kafka.bootstrapAddress}")
+    private String bootstrapAddress;
+
+    @Bean
+    public ProducerFactory<String, String> producerFactory() {
+        Map<String, Object> configProps = new HashMap<String, Object>();
+        configProps.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, bootstrapAddress);
+        configProps.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
+        configProps.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
+        return new DefaultKafkaProducerFactory<String, String>(configProps);
+    }
+
+    @Bean
+    public KafkaTemplate<String, String> kafkaTemplate() {
+        KafkaTemplate<String, String> template = 
+            new KafkaTemplate<String, String>(producerFactory());
+        return template;
+    }
+}

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

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+kafka.bootstrapAddress=localhost:9092
+message.topic.name=baeldung