'Unknown datum type' exception generated by ArrayType elements

[florin1288]

Hello,

Caused by: org.apache.avro.AvroRuntimeException: Unknown datum type [Ljava.lang.Object;: [Ljava.lang.Object;@616f81b5 at org.apache.avro.generic.GenericData.getSchemaName(GenericData.java:636) at org.apache.avro.specific.SpecificData.getSchemaName(SpecificData.java:265) at org.apache.avro.generic.GenericData.resolveUnion(GenericData.java:601) at org.apache.avro.generic.GenericDatumWriter.resolveUnion(GenericDatumWriter.java:151) at org.apache.avro.generic.GenericDatumWriter.write(GenericDatumWriter.java:71) at org.apache.avro.generic.GenericDatumWriter.writeField(GenericDatumWriter.java:114) at org.apache.avro.generic.GenericDatumWriter.writeRecord(GenericDatumWriter.java:104) at org.apache.avro.generic.GenericDatumWriter.write(GenericDatumWriter.java:66) at org.apache.avro.generic.GenericDatumWriter.write(GenericDatumWriter.java:58)

The above exception is triggered in the following scenario:
case class Model(params: Option[List[String]])

The above case class generates the following schema:
{"type":"record","name":"Model","namespace":"Test","fields":[{"name":"params","type":[{"type":"array","items":["string","null"]},"null"]}]}

Now, when I create my converterToAvro:
val structType: StructType = Encoders.product[Model].schema
val converter = createConverterToAvro(structType, recordName, recordNamespace)

...and try to generate my genericRecord:
val record: GenericRecord = converter(item).asInstanceOf[GenericRecord]

...I get the above exception!

This happens because in the implementation of AvroOutputWriter.createConverterToAvro, in the case ArrayType, we have the following:
val targetArray = new Array[Any](sourceArraySize)

...and GenericData.getSchemaName does this check:
if (isArray(datum)) return Type.ARRAY.getName();
protected boolean isArray(Object datum) { return datum instanceof Collection;}

Now scala.Array is not an instance of Collection and it will fail gracefully.
In order to fix this, we can use java.util.ArrayList!!!

[a10y]

We also bumped into this, it appears to be fixed since the merge in upstream Spark by using ArrayList instead of Array apache/spark@9603087#diff-01fea32e6ec6bcf6f34d06282e08705aR103