Polymorphism and inheritance in Avro schemas

I found a better way to solve this problem. Looking at the Schema generation source in Avro, I figured out that internally the class generation logic uses Velocity schemas to generate the classes.

I modified the record.vm template to also implement my specific interface. There is a way to specify the location of velocity directory using the templateDirectory configuration in the maven build plugin.

I also switched to using SpecificDatumWriter instead of reflectDatumWriter.

<plugin>
  <groupId>org.apache.avro</groupId>
  <artifactId>avro-maven-plugin</artifactId>
   <version>${avro.version}</version>
   <executions>
    <execution>
      <phase>generate-sources</phase>
      <goals>
        <goal>schema</goal>
      </goals>
      <configuration>
         <sourceDirectory>${basedir}/src/main/resources/avro/schema</sourceDirectory>
         <outputDirectory>${basedir}/target/java-gen</outputDirectory>
         <fieldVisibility>private</fieldVisibility>
         <stringType>String</stringType>
         <templateDirectory>${basedir}/src/main/resources/avro/velocity-templates/</templateDirectory>
       </configuration>
    </execution>
  </executions>
</plugin>