I am trying to convert a Json string into a generic Java Object, with an Avro Schema.
Below is my code.
String json = "{\"foo\": 30.1, \"bar\": 60.2}";
String schemaLines = "{\"type\":\"record\",\"name\":\"FooBar\",\"namespace\":\"com.foo.bar\",\"fields\":[{\"name\":\"foo\",\"type\":[\"null\",\"double\"],\"default\":null},{\"name\":\"bar\",\"type\":[\"null\",\"double\"],\"default\":null}]}";
InputStream input = new ByteArrayInputStream(json.getBytes());
DataInputStream din = new DataInputStream(input);
Schema schema = Schema.parse(schemaLines);
Decoder decoder = DecoderFactory.get().jsonDecoder(schema, din);
DatumReader<Object> reader = new GenericDatumReader<Object>(schema);
Object datum = reader.read(null, decoder);
I get "org.apache.avro.AvroTypeException: Expected start-union. Got VALUE_NUMBER_FLOAT" Exception.
The same code works, if I don't have unions in the schema. Can someone please explain and give me a solution.
Your schema does not match the schema of the json string. You need to have a different schema that does not have a union in the place of the error but a decimal number. Such schema should then be used as a writer schema while you can freely use the other one as the reader schema.