Polish "Add Kafka sample"

Closes gh-11597

spring-boot-samples/spring-boot-sample-kafka/src/main/java/sample/kafka/Consumer.java

@@ -19,10 +19,11 @@ import org.springframework.kafka.annotation.KafkaListener;
 import org.springframework.stereotype.Component;
 
 @Component
-public class Consumer {
+class Consumer {
 
-	@KafkaListener(topics = "myTopic")
+	@KafkaListener(topics = "testTopic")
 	public void processMessage(SampleMessage message) {
-		System.out.println("consumer has received message : [" + message + "]");
+		System.out.println("Received sample message [" + message + "]");
 	}
+
 }

spring-boot-samples/spring-boot-sample-kafka/src/main/java/sample/kafka/Producer.java

@@ -15,18 +15,21 @@
  */
 package sample.kafka;
 
-import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.kafka.core.KafkaTemplate;
 import org.springframework.stereotype.Component;
 
 @Component
 public class Producer {
 
-	@Autowired
-	private KafkaTemplate kafkaTemplate;
+	private final KafkaTemplate<Object, SampleMessage> kafkaTemplate;
+
+	Producer(KafkaTemplate<Object, SampleMessage> kafkaTemplate) {
+		this.kafkaTemplate = kafkaTemplate;
+	}
 
 	public void send(SampleMessage message) {
-		kafkaTemplate.send("myTopic", message);
-		System.out.println("producer has sent message.");
+		this.kafkaTemplate.send("testTopic", message);
+		System.out.println("Sent sample message [" + message + "]");
 	}
+
 }

spring-boot-samples/spring-boot-sample-kafka/src/main/java/sample/kafka/SampleKafkaApplication.java

@@ -15,8 +15,11 @@
  */
 package sample.kafka;
 
+import org.springframework.boot.ApplicationRunner;
 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.boot.builder.SpringApplicationBuilder;
+import org.springframework.context.annotation.Bean;
 
 @SpringBootApplication
 public class SampleKafkaApplication {
@@ -24,4 +27,10 @@ public class SampleKafkaApplication {
 	public static void main(String[] args) {
 		SpringApplication.run(SampleKafkaApplication.class, args);
 	}
+
+	@Bean
+	public ApplicationRunner runner(Producer producer) {
+		return args -> producer.send(new SampleMessage(1, "A simple test message"));
+	}
+
 }

spring-boot-samples/spring-boot-sample-kafka/src/main/java/sample/kafka/SampleMessage.java

@@ -15,39 +15,37 @@
  */
 package sample.kafka;
 
-public class SampleMessage {
-	private Integer id;
-	private String message;
+import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonProperty;
 
-	public Integer getId() {
-		return id;
+public class SampleMessage {
+
+	private final Integer id;
+
+	private final String message;
+
+	@JsonCreator
+	public SampleMessage(@JsonProperty("id") Integer id,
+			@JsonProperty("message") String message) {
+		this.id = id;
+		this.message = message;
 	}
 
-	public void setId(Integer id) {
-		this.id = id;
+	public Integer getId() {
+		return this.id;
 	}
 
 	public String getMessage() {
-		return message;
-	}
-
-	public void setMessage(String message) {
-		this.message = message;
-	}
-
-	public SampleMessage() {
-	}
-
-	public SampleMessage(Integer id, String message) {
-		this.id = id;
-		this.message = message;
+		return this.message;
 	}
 
 	@Override
 	public String toString() {
-		return "SampleMessage{" +
-				"id=" + id +
-				", message='" + message + '\'' +
-				'}';
+		final StringBuilder sb = new StringBuilder("SampleMessage{");
+		sb.append("id=").append(this.id);
+		sb.append(", message='").append(this.message).append('\'');
+		sb.append('}');
+		return sb.toString();
 	}
+
 }