/avro-json-decoder

JSON decoder for AVRO that infers default values

Primary LanguageJavaApache License 2.0Apache-2.0

avro-json-decoder Build Status

JSON decoder for AVRO that infers default values. Based on org.apache.avro.io.JsonDecoder from AVRO 1.8.2 and org.apache.avro.io.ExtendedJsonDecoder by zolyfarkas.

why

Given this schema (in AVRO IDL)

record User {
  string username;
  union {null, string} name = null;
}

this record is valid and will be decoded properly

{"username":"user1","name":null}

whereas this record

{"username":"user1"}

will produce something like

org.apache.avro.AvroTypeException: Expected field name not found: name
	at org.apache.avro.io.JsonDecoder.doAction(JsonDecoder.java:495)
	at org.apache.avro.io.parsing.Parser.advance(Parser.java:88)
	at org.apache.avro.io.JsonDecoder.advance(JsonDecoder.java:157)
	at org.apache.avro.io.JsonDecoder.readIndex(JsonDecoder.java:447)
	...

or

org.apache.avro.AvroTypeException: Expected start-union. Got END_OBJECT
	at org.apache.avro.io.JsonDecoder.error(JsonDecoder.java:698)
	at org.apache.avro.io.JsonDecoder.readIndex(JsonDecoder.java:441)
	at org.apache.avro.io.ResolvingDecoder.doAction(ResolvingDecoder.java:290)
	at org.apache.avro.io.parsing.Parser.advance(Parser.java:88)
        ...

The decoder allows decoding JSON that doesn't specify optional values, provided they have defaults.

how

Replace

Decoder decoder = DecoderFactory.get().jsonDecoder(SCHEMA, INPUT_STREAM_OR_STRING);

with

Decoder decoder = new ExtendedJsonDecoder(SCHEMA, INPUT_STREAM_OR_STRING);

and pass it to your reader, as usual:

SpecificDatumReader<T> reader = new SpecificDatumReader<>(SCHEMA_OR_CLASS);
reader.read(null, decoder);