Avro Serialization and Deserialization

Avro can be serialized/deserialized by either tools or java code.

1. Avro tools

Serialize Json to Avro with snappy compression
$java -jar avro-tools-1.7.5.jar fromjson --schema-file object.avsc object.json > object.snappy.avro

Deserialize from snappy Avro to Json
$java -jar avro-tools-1.7.5.jar tojson object.snappy.avro > object.json

Retrieve schema from Avro
$java -jar avro-tools-1.7.5.jar getschema object.snappy.avro > object.avsc

2. Java code

We can generate either java code from schema($java -jar avro-tools-1.7.5.jar compile schema object.avsc  <output>), or use a GenericRecord.
The only difference is that values are assigned to a generated Avro object instead of assigning to GenericRecord object.

Example: Convert a Json file to Avro file based on the given schema.

import java.io.File;

04.import java.io.FileInputStream;

05.import java.io.IOException;

06.import java.io.InputStream;

07.import java.util.Iterator;

08.import java.util.LinkedHashMap;

09. 

10.import org.apache.avro.Schema;

11.import org.apache.avro.file.DataFileReader;

12.import org.apache.avro.file.DataFileWriter;

13.import org.apache.avro.generic.GenericData;

14.import org.apache.avro.generic.GenericDatumReader;

15.import org.apache.avro.generic.GenericDatumWriter;

16.import org.apache.avro.generic.GenericRecord;

17.import org.apache.avro.io.BinaryDecoder;

18.import org.apache.avro.io.DatumReader;

19.import org.apache.avro.io.DatumWriter;

20.import org.codehaus.jackson.JsonFactory;

21.import org.codehaus.jackson.JsonParseException;

22.import org.codehaus.jackson.JsonProcessingException;

23.import org.codehaus.jackson.map.ObjectMapper;

24.import org.json.simple.JSONObject;

25. 

26. 

27. 

28.public class AvroExampleWithoutCodeGeneration {

29. 

30.public void serialize() throws JsonParseException, JsonProcessingException, IOException {

31. 

32.InputStream in = new FileInputStream("resources/StudentActivity.json");

33. 

34.// create a schema

35.Schema schema = new Schema.Parser().parse(newFile("resources/StudentActivity.avsc"));

36.// create a record to hold json

37.GenericRecord AvroRec = new GenericData.Record(schema);

38.// create a record to hold course_details

39.GenericRecord CourseRec = newGenericData.Record(schema.getField("course_details").schema());

40.// this file will have AVro output data

41.File AvroFile = new File("resources/StudentActivity.avro");

42.// Create a writer to serialize the record

43.DatumWriter<GenericRecord> datumWriter = newGenericDatumWriter<GenericRecord>(schema);             

44.DataFileWriter<GenericRecord> dataFileWriter = newDataFileWriter<GenericRecord>(datumWriter);

45. 

46.dataFileWriter.create(schema, AvroFile);

47. 

48.// iterate over JSONs present in input file and write to Avro output file

49.for (Iterator it = new ObjectMapper().readValues(

50.new JsonFactory().createJsonParser(in), JSONObject.class); it.hasNext();) {

51. 

52.JSONObject JsonRec = (JSONObject) it.next();

53.AvroRec.put("id", JsonRec.get("id"));

54.AvroRec.put("student_id", JsonRec.get("student_id"));

55.AvroRec.put("university_id", JsonRec.get("university_id"));

56. 

57.LinkedHashMap CourseDetails = (LinkedHashMap) JsonRec.get("course_details");

58.CourseRec.put("course_id", CourseDetails.get("course_id"));

59.CourseRec.put("enroll_date", CourseDetails.get("enroll_date"));

60.CourseRec.put("verb", CourseDetails.get("verb"));

61.CourseRec.put("result_score", CourseDetails.get("result_score"));

62. 

63.AvroRec.put("course_details", CourseRec);

64. 

65.dataFileWriter.append(AvroRec);

66.}  // end of for loop

67. 

68.in.close();

69.dataFileWriter.close();

70. 

71.} // end of serialize method

72. 

73.public void deserialize () throws IOException {

74.// create a schema

75.Schema schema = new Schema.Parser().parse(newFile("resources/StudentActivity.avsc"));

76.// create a record using schema

77.GenericRecord AvroRec = new GenericData.Record(schema);

78.File AvroFile = new File("resources/StudentActivity.avro");

79.DatumReader<GenericRecord> datumReader = newGenericDatumReader<GenericRecord>(schema);

80.DataFileReader<GenericRecord> dataFileReader = newDataFileReader<GenericRecord>(AvroFile, datumReader);

81.System.out.println("Deserialized data is :");

82.while (dataFileReader.hasNext()) {

83.AvroRec = dataFileReader.next(AvroRec);

84.System.out.println(AvroRec);

85.}

86.}

87. 

88.public static void main(String[] args) throws JsonParseException, JsonProcessingException, IOException {

89.AvroExampleWithoutCodeGeneration AvroEx = newAvroExampleWithoutCodeGeneration();

90.AvroEx.serialize();

91.AvroEx.deserialize();

92.}

93.}

Reference:
http://java.dzone.com/articles/getting-started-avro-part-2