Using Mule With Kafka Connector
A Mule loving developer walks us through an experiment he ran where he integrated Mule with Kafka using code from public repositories.
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Join For FreeI 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>
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