This project includes a Maven archetype that can be used for quickly bootstrapping custom KSQL UDFs and UDAFs. Generating a project from this archetype will produce a couple of example functions (a UDF named REVERSE and a UDAF named SUMMARY_STATS) that are ready to be deployed to your KSQL server. Feel free to use these examples as a starting point for your own custom KSQL functions.

First, run the following command to generate a new project from this archetype.

$ mvn archetype:generate -X \
    -DarchetypeGroupId=io.confluent.ksql \
    -DarchetypeArtifactId=ksqldb-udf-quickstart \
    -DarchetypeVersion=6.2.0-SNAPSHOT \
    -DgroupId=com.example.ksql.functions \
    -DartifactId=my-udf \
    -Dauthor=Bob \
    -Dversion=0.1.0-SNAPSHOT

This will copy an example UDF and UDAF into the my-udf directory. Be sure to update the groupId, artifactId, author and version properties in the command above to the appropriate values for your project.

Once you're ready to deploy your custom functions, run the following command to build an uber JAR.

$ mvn clean package

Now, all you need to do is copy the JAR to the KSQL extension directory (see the ksql.extension.dir setting).

# copy the JAR to the KSQL extenstion directory
$ cp target/my-udf-0.1.0-SNAPSHOT.jar /path/to/ext/

Finally, run SHOW FUNCTIONS from the CLI and you should see your new UDF / UDAF in the list :)

You can install this archetype to a local maven repo for testing changes. Simply run the following:

$ mvn install

First, ensure the Nexus credentials are added to $HOME/.m2/settings.xml.

<settings xmlns="http://maven.apache.org/SETTINGS/1.0.0"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0
                       https://maven.apache.org/xsd/settings-1.0.0.xsd">
    <servers>
        <server>
            <username>...</username>
            <password>...</password>
            <id>confluent</id>
        </server>
        <server>
            <username>...</username>
            <password>...</password>
            <id>confluent-snapshots</id>
        </server>
  </servers>
</settings>

Then, simply run:

$ mvn deploy