JSON to Avro conversion tool designed to make migration to Avro easier.
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Latest commit dcff6e9 May 20, 2018



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JSON to Avro conversion tool designed to make migration to Avro easier. Includes simple command line validator.


Apache Avro ships with some very advanced and efficient tools for reading and writing binary Avro but their support for JSON to Avro conversion is unfortunately limited and requires wrapping fields with type declarations if you have some optional fields in your schema. This tool is supposed to help with migrating project from using JSON to Avro without having to modify JSON data if it conforms to the JSON schema.

JSON2Avro Converter


  • conversion binary JSON to binary Avro
  • conversion binary JSON to GenericData.Record
  • conversion binary JSON to Avro generated Java classes
  • conversion binary Avro to binary JSON
  • optional field support (unions do not require wrapping)
  • unknown fields that are not declared in schema are ignored


dependencies {
    compile group: 'tech.allegro.schema.json2avro', name: 'converter', version: '0.2.6'

Basic usage

import tech.allegro.schema.json2avro.converter.AvroConversionException;
import tech.allegro.schema.json2avro.converter.JsonAvroConverter;
import org.apache.avro.generic.GenericData;
import org.apache.avro.Schema;

// Avro schema with one string field: username
String schema =
            "{" +
            "   \"type\" : \"record\"," +
            "   \"name\" : \"Acme\"," +
            "   \"fields\" : [{ \"name\" : \"username\", \"type\" : \"string\" }]" +

String json = "{ \"username\": \"mike\" }";

JsonAvroConverter converter = new JsonAvroConverter();

// conversion to binary Avro
byte[] avro = converter.convertToAvro(json.getBytes(), schema);

// conversion to GenericData.Record
GenericData.Record record = converter.convertToGenericDataRecord(json.getBytes(), new Schema.Parser().parse(schema));

// conversion from binary Avro to JSON
byte[] binaryJson = converter.convertToJson(avro, schema);

// exception handling
String invalidJson = "{ \"username\": 8 }";    

try {
    converter.convertToAvro(invalidJson.getBytes(), schema);    
} catch (AvroConversionException ex) {
    System.err.println("Caught exception: " + ex.getMessage());


A command line tool for validating your JSON/Avro documents against the schema.


To bundle the tool into single executable JAR:

./gradlew :validator:shadowJar
java -jar validator/build/libs/json2avro-validator-{version}.jar --help


Running Validator with --help option will print help message listing all possible arguments. Sample Avro schema and messages can be found in:

  • schema: validator/src/test/resources/user.avcs
  • JSON message: validator/src/test/resources/user.json
  • Avro message: validator/src/test/resources/user.avro

JSON to Avro

You can validate your JSON to Avro conversion:

java -jar json2avro-validator.jar -s user.avcs -i user.json

If everything will process correctly, the process will end with zero status code.

Avro to JSON

You can convert the Avro binary data into JSON by setting mode -m avro2json option:

java -jar json2avro-validator.jar -s user.avcs -i user.avro -m avro2json

JSON to Avro to JSON

If you would like to know how message will look like after encoding and decoding invoke:

java -jar json2avro-validator.jar -s user.avcs -i user.json -m json2avro2json


json-avro-converter is published under Apache License 2.0.