Question

尽管为字段定义了默认值，但是kafka-avro-console-producer会完全忽略它：

$ kafka-avro-console-producer --broker-list localhost:9092 --topic test-avro \
--property schema.registry.url=http://localhost:8081 --property \
value.schema='{"type":"record","name":"myrecord1","fields": \
[{"name":"f1","type":"string"},{"name": "f2", "type": "int", "default": 0}]}'

{"f1": "value1"}

org.apache.kafka.common.errors.SerializationException: Error 
deserializing json {"f1": "value1"} to Avro of schema 
{"type":"record","name":"myrecord1","fields": 
[{"name":"f1","type":"string"},{"name":"f2","type":"int","default":0}]}
Caused by: org.apache.avro.AvroTypeException: Expected int. Got END_OBJECT
    at org.apache.avro.io.JsonDecoder.error(JsonDecoder.java:698)
    at org.apache.avro.io.JsonDecoder.readInt(JsonDecoder.java:172)
    at org.apache.avro.io.ValidatingDecoder.readInt(ValidatingDecoder.java:83)
    at org.apache.avro.generic.GenericDatumReader.readInt(GenericDatumReader.java:511)
    at org.apache.avro.generic.GenericDatumReader.readWithoutConversion(GenericDatumReader.java:182)
    at org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:152)
    at org.apache.avro.generic.GenericDatumReader.readField(GenericDatumReader.java:240)
    at org.apache.avro.generic.GenericDatumReader.readRecord(GenericDatumReader.java:230)
    at org.apache.avro.generic.GenericDatumReader.readWithoutConversion(GenericDatumReader.java:174)
    at org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:152)
    at org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:144)
    at io.confluent.kafka.formatter.AvroMessageReader.jsonToAvro(AvroMessageReader.java:213)
    at io.confluent.kafka.formatter.AvroMessageReader.readMessage(AvroMessageReader.java:180)
    at kafka.tools.ConsoleProducer$.main(ConsoleProducer.scala:54)
    at kafka.tools.ConsoleProducer.main(ConsoleProducer.scala)

然后如何使用它才能接受默认值？顶层配置设置为"BACKWARD"兼容性级别检查，尽管我认为这与问题无关。该模式是版本2，版本1仅定义了f1字段，但是正如我所说，我认为这无关紧要。

Answer 1

该错误表示该消息与您定义的Avro模式不兼容。据我了解，您想为字段null允许f2的值。为此，您需要将value.schema更改为（注意"type"的定义）：

value.schema='{"type":"record","name":"myrecord1","fields": [{"name":"f1","type":"string"},{"name": "f2", "type": ["null", "int"], "default": 0}]}'

，但是您仍然需要使用空值定义f2键。以下应该为您解决问题：

kafka-avro-console-producer --broker-list localhost:9092 --topic test-avro \ 
    --property schema.registry.url=http://localhost:8081 \ 
    --property value.schema='{"type":"record","name":"myrecord1","fields": [{"name":"f1","type":"string"},{"name": "f2", "type": ["null", "int"], "default": 0}]}'

{"f1":"value1","f2":null}

您可以使用kafka-avro-console-consumer确认它是否有效：

kafka-avro-console-consumer --bootstrap-server localhost:9092 --topic test-avro --from-beginning
{"f1":"value1","f2":null}
^CProcessed a total of 1 messages

Answer 2

根据Avro spec

的定义

default：此字段的默认值，在读取缺少该字段的实例时使用

因此，生产者仍然需要提供该字段。

我不确定使用Avro控制台生成器时是否可以完全排除该字段，因为即使您将该字段设置为Giorgos所示的可空值，您仍然需要显式设置它。

为什么kafka-avro-console-producer不遵守该字段的默认值？

2 个答案: