I wanted to experiment with Kafka and Mule with Maven utilizing the public repositories. Their connector is:

<dependency>
  <groupId>org.mule.modules</groupId>
  <artifactId>mule-module-kafka</artifactId>
  <version>2.1.0</version>
</dependency>

I was disappointed when the build came back with:

[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 3.851 s
[INFO] Finished at: 2018-01-28T01:20:13-05:00
[INFO] Final Memory: 25M/269M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal on project demo-mule-spring-boot: Could not resolve dependencies for project net.taptech:demo-mule-spring-boot:jar:0.0.1-SNAPSHOT: Could not find artifact org.mule.modules:mule-module-kafka:jar:2.1.0 in Central (http://repo1.maven.org/maven2/) -> [Help 1]

After checking the repositories, I found that the connector was a select connector. Information on Mule connectors can be found here.

After getting that information, I decided to build an open source version of the connector using Apache Kafka clients and streams version 1.

Let's take a look at what I was able to build. Here is the Maven dependency to use:

<dependency>
    <groupId>net.taptech</groupId>
    <artifactId>mule-kafka-connector</artifactId>
    <version>1.1.0</version>
</dependency>

My use cases were to use the connector as producers and consumers of Kafka topics.

The consumer endpoint can be used as an inbound endpoint:

<kafka:consumer config-ref="kafka-config" topic="streams-plaintext-input"/>

Place this in your Mule flows as you would an inbound endpoint.

Example:

<flow name="streams-plaintext-input">
        <kafka:consumer config-ref="kafka-config" topic="streams-plaintext-input"/>
        <foreach doc:name="Foreach" collection="#[payload.iterator()]">
            <logger message="consumer received from topic [#[payload.topic()]] key => [#[payload.key()]] value => [#[payload.value()]] "
                    category="net.taptech.kafka.mule.word-count-flow" level="INFO" doc:name="Consumed message logger"/>
        </foreach>
    </flow>

The payload returned is a List<ConsumerRecord<K, V>>. A Consumer record is defined by Kafka here.

There is a similar producer as well:

<kafka:producer config-ref="kafka-config" topic="streams-plaintext-input" key="#[flowVars['recordKey']]"
                        message="#[payload]"/>

This produces a list of RecordMetadata, which can be found here.

One of the current limitations is the key and the message should be of type String.

Of course, there is a config and it looks similar to this:

<kafka:config name="kafka-config" consumerPropertiesFile="kafka-consumer.properties"
                  producerPropertiesFile="kafka-producer.properties"/>

One of the big features of Kafka is the ability to go back and get messages. I also provide a way to get messages from an offset. I have implemented that feature here:

<kafka:seek config-ref="kafka-config" partition="#[flowVars.partition]" topic="#[flowVars.topic]" offset="#[flowVars.offset]"/>

kafka-consumer.properties and kafka-producer.properties should be available on the classpath.

This also returns a List<ConsumerRecord<K, V>> to the payload.

You can also override the properties given in the config by setting the propertyFileOverrides attribute.

 <kafka:consumer config-ref="kafka-config" topic="streams-plaintext-input"
                        propertyFileOverrides="kafka-alternate.properties"/>

In this case, the kafka-alternate.properties should be available on the classpath.

You can download the sample project from my GitHub.

MAKE SURE YOU SWITCH to the kafka-example branch.

After starting Kafka locally, run this command:

./mvnw clean package -Dmaven.test.skip=true && java -jar target/demo-mule-spring-boot-0.0.1-SNAPSHOT.jar

Here is the sample mule-config.xml

<?xml version="1.0" encoding="UTF-8"?>

<mule xmlns:http="http://www.mulesoft.org/schema/mule/http" xmlns="http://www.mulesoft.org/schema/mule/core"
      xmlns:doc="http://www.mulesoft.org/schema/mule/documentation"
      xmlns:kafka="http://www.mulesoft.org/schema/mule/kafka"
      xmlns:json="http://www.mulesoft.org/schema/mule/json"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:schemaLocation="http://www.mulesoft.org/schema/mule/core http://www.mulesoft.org/schema/mule/core/current/mule.xsd
      http://www.mulesoft.org/schema/mule/kafka http://www.mulesoft.org/schema/mule/kafka/current/mule-kafka.xsd
http://www.mulesoft.org/schema/mule/http http://www.mulesoft.org/schema/mule/http/current/mule-http.xsd
http://www.mulesoft.org/schema/mule/json http://www.mulesoft.org/schema/mule/json/current/mule-json.xsd">
    <http:listener-config name="HTTP_Listener_Configuration" host="0.0.0.0" port="8081"
                          doc:name="HTTP Listener Configuration"/>

    <kafka:config name="kafka-config" consumerPropertiesFile="kafka-consumer.properties"
                  producerPropertiesFile="kafka-producer.properties"/>

    <flow name="mule-demo-filesFlow1">
        <http:listener config-ref="HTTP_Listener_Configuration" path="/payload" allowedMethods="POST" doc:name="HTTP"/>

        <logger message="New message #[message] arrived: #[payload]" category="org.mule.module.kafka" level="INFO"
                doc:name="Consumed message logger"/>
        <object-to-string-transformer/>
        <set-variable variableName="recordKey" value="#[java.util.UUID.randomUUID().toString()]"/>
        <kafka:producer config-ref="kafka-config" topic="streams-plaintext-input" key="#[flowVars['recordKey']]"
                        message="#[payload]"/>
        <transformer ref="recordMetadataListToJsonTransformer"/>
    </flow>

    <flow name="mule-demo-filesFlow2">
        <http:listener config-ref="HTTP_Listener_Configuration" path="/payload" allowedMethods="GET" doc:name="HTTP"/>
        <set-variable variableName="offset" value="#[message.inboundProperties.'http.query.params'.offset]"/>
        <set-variable variableName="partition" value="#[message.inboundProperties.'http.query.params'.partition]"/>
        <set-variable variableName="topic" value="#[message.inboundProperties.'http.query.params'.topic]"/>

        <logger message="New message #[message] arrived: #[payload]" category="org.mule.module.kafka" level="INFO"
                doc:name="Consumed message logger"/>
        <kafka:seek config-ref="kafka-config" partition="#[flowVars.partition]" topic="#[flowVars.topic]"
                    offset="#[flowVars.offset]"/>
        <transformer ref="consumerRecordListToJsonTransformer"/>
    </flow>


    <flow name="streams-plaintext-input">
        <kafka:consumer config-ref="kafka-config" topic="streams-plaintext-input"
                        propertyFileOverrides="kafka-alternate.properties"/>
        <foreach doc:name="Foreach" collection="#[payload.iterator()]">
            <logger message="consumer received from topic [#[payload.topic()]] key => [#[payload.key()]] value => [#[payload.value()]] "
                    category="net.taptech.kafka.mule.word-count-flow" level="INFO" doc:name="Consumed message logger"/>
        </foreach>
    </flow>

</mule>