How generate Avro Schema with Jackson without Java types

Question

I am currently trying to generate a schema using the Avro Generator from Jackson. I'm surprised that there are many Java classes in the schema.

I'm not an avro expert, but the format looks kind of weird and not correct

DTO:

public class TestDto {

   @JsonProperty( "id" )
   private Long id;

   @JsonProperty( "labels" )
   @Valid
   private Set<String> labels;
}

Mapper:

   private AvroSchema generateAvroSchema(  ) throws JsonMappingException {
      AvroMapper avroMapper = new AvroMapper();
      final AvroSchemaGenerator gen = new AvroSchemaGenerator();
      avroMapper.acceptJsonFormatVisitor( TestDto.class, gen );

      return gen.getGeneratedSchema();
   }

Schema:

{
  "type": "record",
  "name": "TestDto",
  "namespace": "test.model",
  "fields": [
    {
      "name": "id",
      "type": [
        "null",
        {
          "type": "long",
          "java-class": "java.lang.Long"
        }
      ]
    },
    {
      "name": "labels",
      "type": [
        "null",
        {
          "type": "array",
          "items": "string",
          "java-class": "java.util.Set"
        }
      ]
    }
  ]
}

Can this scheme be used at all by other languages such as Python?

Why are you using Jackson (primarily an over-engineered JSON parsing library) to deal with Avro, and not just using the Avro Java library directly? — jon hanson, May 08 '23 at 19:55
@jon-hanson first idea was to reuse the generated DTOs classes from open api and not to manually create additional avro schemas, but in the meanwhile I found a option in the open api generator to generated avro schemas. So now I generate avro schemas from open api and then generate the avro classes. — MelleD, May 09 '23 at 09:23

jon hanson · Accepted Answer · 2023-05-08T20:21:13.323

The "java-class" entry is used to determine which Java implementation class the field corresponds to when a schema is generated dynamically. Other languages will generally ignore that information, so the schema should be usuable by other languages.

The Avro guide doesn't seem to describe this anywhere, however it is mentioned in the Avro reflection Javadocs

Collection implementations are mapped to Avro array schemas with the "java-class" property set to the collection implementation, e.g.:

{"type": "array", "java-class": "java.util.ArrayList"}

Also the IDL language has a direct counterpart, that's documented here.

How generate Avro Schema with Jackson without Java types

1 Answers1