问答:Json String to Java Object Avro - 问答

我得到"org.apache.avro.AvroTypeException:期望的start-union.得到VALUE_NUMBER_FLOAT"异常.

如果模式中没有联合,则相同的代码可以工作.有人可以解释并给我一个解决方案.

3 个回答

感谢Reza.我找到了这个网页.它介绍了如何将Json字符串转换为avro对象.

http://rezarahim.blogspot.com/2013/06/import-org_26.html

他的代码的关键是:

static byte[] fromJsonToAvro(String json, String schemastr) throws Exception {
  InputStream input = new ByteArrayInputStream(json.getBytes());
  DataInputStream din = new DataInputStream(input);

  Schema schema = Schema.parse(schemastr);

  Decoder decoder = DecoderFactory.get().jsonDecoder(schema, din);

  DatumReader<Object> reader = new GenericDatumReader<Object>(schema);
  Object datum = reader.read(null, decoder);

  GenericDatumWriter<Object>  w = new GenericDatumWriter<Object>(schema);
  ByteArrayOutputStream outputStream = new ByteArrayOutputStream();

  Encoder e = EncoderFactory.get().binaryEncoder(outputStream, null);

  w.write(datum, e);
  e.flush();

  return outputStream.toByteArray();
}

String json = "{\"username\":\"miguno\",\"tweet\":\"Rock: Nerf paper, scissors is fine.\",\"timestamp\": 1366150681 }";

String schemastr ="{ \"type\" : \"record\", \"name\" : \"twitter_schema\", \"namespace\" : \"com.miguno.avro\", \"fields\" : [ { \"name\" : \"username\", \"type\" : \"string\", \"doc\"  : \"Name of the user account on Twitter.com\" }, { \"name\" : \"tweet\", \"type\" : \"string\", \"doc\"  : \"The content of the user's Twitter message\" }, { \"name\" : \"timestamp\", \"type\" : \"long\", \"doc\"  : \"Unix epoch time in seconds\" } ], \"doc:\" : \"A basic schema for storing Twitter messages\" }";

byte[] avroByteArray = fromJsonToAvro(json,schemastr);

Schema schema = Schema.parse(schemastr);
DatumReader<Genericrecord> reader1 = new GenericDatumReader<Genericrecord>(schema);

Decoder decoder1 = DecoderFactory.get().binaryDecoder(avroByteArray, null);
GenericRecord result = reader1.read(null, decoder1);

2022-12-11 02:08 回答

董鹏飞80

对于使用Avro-1.8.2的任何人，JsonDecoder现在都无法在程序包外部直接实例化org.apache.avro.io。您可以使用DecoderFactory它，如以下代码所示：

String schemaStr = "<some json schema>";
String genericRecordStr = "<some json record>";
Schema.Parser schemaParser = new Schema.Parser();
Schema schema = schemaParser.parse(schemaStr);
DecoderFactory decoderFactory = new DecoderFactory();
Decoder decoder = decoderFactory.jsonDecoder(schema, genericRecordStr);
DatumReader<GenericData.Record> reader =
            new GenericDatumReader<>(schema);
GenericRecord genericRecord = reader.read(null, decoder);

2022-12-11 02:10 回答

霸气小米鱼鱼_156

使用Avro 1.4.1,这适用于:

private static GenericData.Record parseJson(String json, String schema)
    throws IOException {
  Schema parsedSchema = Schema.parse(schema);
  Decoder decoder = new JsonDecoder(parsedSchema, json);

  DatumReader<GenericData.Record> reader =
      new GenericDatumReader<>(parsedSchema);
  return reader.read(null, decoder);
}

可能需要对以后的Avro版本进行一些调整.

2022-12-11 02:57 回答

信妹氵V