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In this article we will learn how to connect to Apache Kafka cluster from a Camel route using the Camel Kafka Consumer and Producer.

Perform the following preliminary actions:

Start the Zookeeper Server

Start the ZooKeeper server. Kafka provides a simple ZooKeeper configuration file to launch a single ZooKeeper instance. To install the ZooKeeper instance, use the following command:

bin/zookeeper-server-start.sh config/zookeeper.properties
 
[2020-04-14 19:42:12,456] INFO binding to port 0.0.0.0/0.0.0.0:2181 (org.apache.zookeeper.server.NIOServerCnxnFactory)
[2020-04-14 19:42:12,470] INFO zookeeper.snapshotSizeFactor = 0.33 (org.apache.zookeeper.server.ZKDatabase)
[2020-04-14 19:42:12,475] INFO Snapshotting: 0x0 to /tmp/zookeeper/version-2/snapshot.0 (org.apache.zookeeper.server.persistence.FileTxnSnapLog)
[2020-04-14 19:42:12,480] INFO Snapshotting: 0x0 to /tmp/zookeeper/version-2/snapshot.0 (org.apache.zookeeper.server.persistence.FileTxnSnapLog)
[2020-04-14 19:42:12,496] INFO Using checkIntervalMs=60000 maxPerMinute=10000 (org.apache.zookeeper.server.ContainerManager)

Start Apache Kafka

Now, start the Kafka broker with the following command:

bin/kafka-server-start.sh config/server.properties

[2020-04-14 19:43:13,350] INFO Kafka version: 2.4.1 (org.apache.kafka.common.utils.AppInfoParser)
[2020-04-14 19:43:13,350] INFO Kafka commitId: c57222ae8cd7866b (org.apache.kafka.common.utils.AppInfoParser)
[2020-04-14 19:43:13,351] INFO Kafka startTimeMs: 1586886193347 (org.apache.kafka.common.utils.AppInfoParser)
[2020-04-14 19:43:13,352] INFO [KafkaServer id=0] started (kafka.server.KafkaServer)

Now that Apache Kafka is started, create a Topic that will be using in our application:

bin/kafka-topics.sh --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic myTopic

Create the Camel Project

You can create a Camel 3 project using its archetype:

mvn archetype:generate \
 -DarchetypeGroupId=org.apache.camel.archetypes \
 -DarchetypeArtifactId=camel-archetype-java \
 -DarchetypeVersion=3.0.0 \
 -DgroupId=com.sample.camel \
 -DartifactId=camel-kafka \
 -Dversion=1.0-SNAPSHOT

 

A basic project will be created. Now replace the RouteBuilder class with the following one, which sends the messages contained in the data folder to the Kafka topic named 'myTopic'. At the same time, we will be consuming messages with a simple Kafka Consumer:

package com.sample.camel;

import org.apache.camel.builder.RouteBuilder;
import org.apache.camel.component.kafka.KafkaConstants;

/**
 * A Camel Java DSL Router
 */
public class MyRouteBuilder extends RouteBuilder {

    /**
     * Let's configure the Camel routing rules using Java code...
     */
    @Override
    public void configure() throws Exception {

        // Kafka Producer
        from("file:src/data?noop=true")
                 .setHeader(KafkaConstants.KEY, constant("Camel")) // Key of the message
                .to("kafka:myTopic?brokers=localhost:9092");

        // Kafka Consumer
        from("kafka:myTopic?brokers=localhost:9092")
                .log("Message received from Kafka : ${body}")
                .log("    on the topic ${headers[kafka.TOPIC]}")
                .log("    on the partition ${headers[kafka.PARTITION]}")
                .log("    with the offset ${headers[kafka.OFFSET]}")
                .log("    with the key ${headers[kafka.KEY]}");
    }

}

That's all. run the project. Run the main class and verify that the messages are logged on the Console:

<person user="james">
  <firstName>James</firstName>
  <lastName>Strachan</lastName>
  <city>London</city>
</person>
[ad #3 - KafkaConsumer[myTopic]] route2                         INFO      on the topic myTopic
[ad #3 - KafkaConsumer[myTopic]] route2                         INFO      on the partition 0
[ad #3 - KafkaConsumer[myTopic]] route2                         INFO      with the offset 6
[ad #3 - KafkaConsumer[myTopic]] route2                         INFO      with the key Camel
[ad #3 - KafkaConsumer[myTopic]] route2                         INFO  Message received from Kafka : <?xml version="1.0" encoding="UTF-8"?>
<person user="hiram">
  <firstName>Hiram</firstName>
  <lastName>Chirino</lastName>
  <city>Tampa</city>
</person>
[ad #3 - KafkaConsumer[myTopic]] route2                         INFO      on the topic myTopic
[ad #3 - KafkaConsumer[myTopic]] route2                         INFO      on the partition 0
[ad #3 - KafkaConsumer[myTopic]] route2                         INFO      with the offset 7
[ad #3 - KafkaConsumer[myTopic]] route2                         INFO      with the key Camel

Source code for this tutorial: http://www.masterspringboot.com/various/camel/consuming-and-producing-kafka-messages-from-camel

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