How to Avro Binary encode the JSON String using Apache Avro?

arrays, avro, binary, java, json

Solution

I think OP is correct. This will write Avro records themselves without the schema that would be present if this were an Avro data file.

Here's a couple examples within Avro itself (useful if you are working with files. • From JSON to Avro: DataFileWriteTool • From Avro to JSON: DataFileReadTool

Here's a complete example going both ways.

@Grapes([
    @Grab(group='org.apache.avro', module='avro', version='1.7.7')
])

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.DataInputStream;
import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;

import org.apache.avro.Schema;
import org.apache.avro.generic.GenericDatumReader;
import org.apache.avro.generic.GenericDatumWriter;
import org.apache.avro.generic.GenericRecord;
import org.apache.avro.io.DatumReader;
import org.apache.avro.io.DatumWriter;
import org.apache.avro.io.Decoder;
import org.apache.avro.io.DecoderFactory;
import org.apache.avro.io.Encoder;
import org.apache.avro.io.EncoderFactory;
import org.apache.avro.io.JsonEncoder;

String schema = '''{
  "type":"record",
  "namespace":"foo",
  "name":"Person",
  "fields":[
    {
      "name":"name",
      "type":"string"
    },
    {
      "name":"age",
      "type":"int"
    }
  ]
}'''
String json = "{" +
  "\"name\":\"Frank\"," +
  "\"age\":47" +
"}"

assert avroToJson(jsonToAvro(json, schema), schema) == json


public static byte[] jsonToAvro(String json, String schemaStr) throws IOException {
    InputStream input = null;
    GenericDatumWriter<GenericRecord> writer = null;
    Encoder encoder = null;
    ByteArrayOutputStream output = null;
    try {
        Schema schema = new Schema.Parser().parse(schemaStr);
        DatumReader<GenericRecord> reader = new GenericDatumReader<GenericRecord>(schema);
        input = new ByteArrayInputStream(json.getBytes());
        output = new ByteArrayOutputStream();
        DataInputStream din = new DataInputStream(input);
        writer = new GenericDatumWriter<GenericRecord>(schema);
        Decoder decoder = DecoderFactory.get().jsonDecoder(schema, din);
        encoder = EncoderFactory.get().binaryEncoder(output, null);
        GenericRecord datum;
        while (true) {
            try {
                datum = reader.read(null, decoder);
            } catch (EOFException eofe) {
                break;
            }
            writer.write(datum, encoder);
        }
        encoder.flush();
        return output.toByteArray();
    } finally {
        try { input.close(); } catch (Exception e) { }
    }
}

public static String avroToJson(byte[] avro, String schemaStr) throws IOException {
    boolean pretty = false;
    GenericDatumReader<GenericRecord> reader = null;
    JsonEncoder encoder = null;
    ByteArrayOutputStream output = null;
    try {
        Schema schema = new Schema.Parser().parse(schemaStr);
        reader = new GenericDatumReader<GenericRecord>(schema);
        InputStream input = new ByteArrayInputStream(avro);
        output = new ByteArrayOutputStream();
        DatumWriter<GenericRecord> writer = new GenericDatumWriter<GenericRecord>(schema);
        encoder = EncoderFactory.get().jsonEncoder(schema, output, pretty);
        Decoder decoder = DecoderFactory.get().binaryDecoder(input, null);
        GenericRecord datum;
        while (true) {
            try {
                datum = reader.read(null, decoder);
            } catch (EOFException eofe) {
                break;
            }
            writer.write(datum, encoder);
        }
        encoder.flush();
        output.flush();
        return new String(output.toByteArray());
    } finally {
        try { if (output != null) output.close(); } catch (Exception e) { }
    }
}

For the sake of completeness, here's an example if you were working with streams (Avro calls these container files) instead of records. Note that when you go back from JSON to Avro, you don't need to pass the schema. This is because it is present in the stream.

@Grapes([
    @Grab(group='org.apache.avro', module='avro', version='1.7.7')
])

// writes Avro as a http://avro.apache.org/docs/current/spec.html#Object+Container+Files rather than a sequence of records

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.DataInputStream;
import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;

import org.apache.avro.Schema;
import org.apache.avro.file.DataFileStream;
import org.apache.avro.file.DataFileWriter;
import org.apache.avro.generic.GenericDatumReader;
import org.apache.avro.generic.GenericDatumWriter;
import org.apache.avro.generic.GenericRecord;
import org.apache.avro.io.DatumReader;
import org.apache.avro.io.DatumWriter;
import org.apache.avro.io.Decoder;
import org.apache.avro.io.DecoderFactory;
import org.apache.avro.io.Encoder;
import org.apache.avro.io.EncoderFactory;
import org.apache.avro.io.JsonEncoder;


String schema = '''{
  "type":"record",
  "namespace":"foo",
  "name":"Person",
  "fields":[
    {
      "name":"name",
      "type":"string"
    },
    {
      "name":"age",
      "type":"int"
    }
  ]
}'''
String json = "{" +
  "\"name\":\"Frank\"," +
  "\"age\":47" +
"}"

assert avroToJson(jsonToAvro(json, schema)) == json


public static byte[] jsonToAvro(String json, String schemaStr) throws IOException {
    InputStream input = null;
    DataFileWriter<GenericRecord> writer = null;
    Encoder encoder = null;
    ByteArrayOutputStream output = null;
    try {
        Schema schema = new Schema.Parser().parse(schemaStr);
        DatumReader<GenericRecord> reader = new GenericDatumReader<GenericRecord>(schema);
        input = new ByteArrayInputStream(json.getBytes());
        output = new ByteArrayOutputStream();
        DataInputStream din = new DataInputStream(input);
        writer = new DataFileWriter<GenericRecord>(new GenericDatumWriter<GenericRecord>());
        writer.create(schema, output);
        Decoder decoder = DecoderFactory.get().jsonDecoder(schema, din);
        GenericRecord datum;
        while (true) {
            try {
                datum = reader.read(null, decoder);
            } catch (EOFException eofe) {
                break;
            }
            writer.append(datum);
        }
        writer.flush();
        return output.toByteArray();
    } finally {
        try { input.close(); } catch (Exception e) { }
    }
}

public static String avroToJson(byte[] avro) throws IOException {
    boolean pretty = false;
    GenericDatumReader<GenericRecord> reader = null;
    JsonEncoder encoder = null;
    ByteArrayOutputStream output = null;
    try {
        reader = new GenericDatumReader<GenericRecord>();
        InputStream input = new ByteArrayInputStream(avro);
        DataFileStream<GenericRecord> streamReader = new DataFileStream<GenericRecord>(input, reader);
        output = new ByteArrayOutputStream();
        Schema schema = streamReader.getSchema();
        DatumWriter<GenericRecord> writer = new GenericDatumWriter<GenericRecord>(schema);
        encoder = EncoderFactory.get().jsonEncoder(schema, output, pretty);
        for (GenericRecord datum : streamReader) {
            writer.write(datum, encoder);
        }
        encoder.flush();
        output.flush();
        return new String(output.toByteArray());
    } finally {
        try { if (output != null) output.close(); } catch (Exception e) { }
    }
}

Problem

Original source