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https://issues.apache.org/jira/browse/AVRO-2702?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17217746#comment-17217746
]
Vladimir Kralik commented on AVRO-2702:
---------------------------------------
h2. WorkAround for Jackson-serialization
h4. Jackson Initialisation
{code:java}
Jackson2ObjectMapperBuilder jackson2ObjectMapperBuilder = new
Jackson2ObjectMapperBuilder();
jackson2ObjectMapperBuilder.mixIn(AvroObject.class, AvroObjectMixIn.class);
{code}
h4. MixIn definition
{code:java}
public interface AvroObjectMixIn {
@JsonIgnore Schema getSchema();
@JsonIgnore SpecificData getSpecificData();
@JsonSerialize(using=AvroListStringSerializer.class)
List<java.lang.String> getListOfString();
}
{code}
h4. Serializer implementation
{code:java}
public class AvroListStringSerializer extends JsonSerializer<List<String>> {
@Override
public void serialize(List<String> value, JsonGenerator gen,
SerializerProvider serializers) throws IOException {
gen.writeStartArray();
if (CollectionUtils.isNotEmpty(value)) {
for (Object o : value) {
gen.writeString(o.toString());
}
}
gen.writeEndArray();
}
}
{code}
> Avro ResolvingGrammarGenerator does not honor "avro.java.string" property in
> inner record schemas
> -------------------------------------------------------------------------------------------------
>
> Key: AVRO-2702
> URL: https://issues.apache.org/jira/browse/AVRO-2702
> Project: Apache Avro
> Issue Type: Bug
> Components: java
> Affects Versions: 1.9.1
> Reporter: Thorsten Hake
> Priority: Major
> Labels: ClassCastException, Deserialize
> Attachments: Bar.kt
>
>
> The type property "avro.java.string" is being used to qualify the
> CharSequence implementation of a string type in java. This property will be
> set in the java code generated by the avro maven plugin, if the <stringType>
> property is set to "String".
> However the ResolvingGrammarGenerator, which helps in matching the writer
> schema to the reader schema, does not honor this property for inner records
> within unions. Instead of deserializing to java.lang.String, the strings of
> the inner record will be deserialized to org.apache.avro.util.Utf8. String
> properties belonging to the outer record will be correctly deserialized to
> java.lang.String.
> If you try to deserialize an Avro record from a schema that has an inner
> record within an union type with the java code generated by the maven plugin
> (<stringType> is set to "String"), you'll get a ClassCastException:
> {noformat}
> Caused by: java.lang.ClassCastException: class org.apache.avro.util.Utf8
> cannot be cast to class java.lang.String
> {noformat}
> This is because the generated java code expects the strings to be
> deserialized according to the "avro.java.string" property which does not
> happen for the inner record.
> I would expect that the deserializer treats the strings in the inner record
> the same as the strings in the outer record.
> Example:
> writer schema:
> {code:json}
> {
> "type": "record",
> "name": "foo",
> "fields": [
> {
> "name": "k",
> "type": "string"
> },
> {
> "name": "value",
> "type": [
> "null",
> {
> "type": "record",
> "name": "bar",
> "fields": [
> {
> "name": "str",
> "type": "string"
> }
> ]
> }
> ]
> }
> ]
> }
> {code}
> reader schema:
> {code:json}
> {
> "type": "record",
> "name": "foo",
> "fields": [
> {
> "name": "k",
> "type": {
> "type": "string",
> "avro.java.string": "String"
> }
> },
> {
> "name": "value",
> "type": [
> "null",
> {
> "type": "record",
> "name": "bar",
> "fields": [
> {
> "name": "str",
> "type": {
> "type": "string",
> "avro.java.string": "String"
> }
> }
> ]
> }
> ]
> }
> ]
> }
> {code}
> You'll find some example kotlin code demonstrating the problem in the
> attached Bar.kt.
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