Using apache avro reflect

Question

Avro serialization is popular with Hadoop users but examples are so hard to find.

Can anyone help me with this sample code? I'm mostly interested in using the Reflect API to read/write into files and to use the Union and Null annotations.

public class Reflect {      public class Packet {         int cost;         @Nullable TimeStamp stamp;         public Packet(int cost, TimeStamp stamp){             this.cost = cost;             this.stamp = stamp;         }     }      public class TimeStamp {         int hour = 0;         int second = 0;         public TimeStamp(int hour, int second){             this.hour = hour;             this.second = second;         }     }      public static void main(String[] args) throws IOException {         TimeStamp stamp;         Packet packet;          stamp = new TimeStamp(12, 34);         packet = new Packet(9, stamp);         write(file, packet);          packet = new Packet(8, null);         write(file, packet);         file.close();          // open file to read.         packet = read(file);         packet = read(file);     } } 

Answer 1

Here's a version of the above program that works.

This also uses compression on the file.

import java.io.File; import org.apache.avro.Schema; import org.apache.avro.file.DataFileWriter; import org.apache.avro.file.DataFileReader; import org.apache.avro.file.CodecFactory; import org.apache.avro.io.DatumWriter; import org.apache.avro.io.DatumReader; import org.apache.avro.reflect.ReflectData; import org.apache.avro.reflect.ReflectDatumWriter; import org.apache.avro.reflect.ReflectDatumReader; import org.apache.avro.reflect.Nullable;  public class Reflect {    public static class Packet {     int cost;     @Nullable TimeStamp stamp;     public Packet() {}                        // required to read     public Packet(int cost, TimeStamp stamp){       this.cost = cost;       this.stamp = stamp;     }   }    public static class TimeStamp {     int hour = 0;     int second = 0;     public TimeStamp() {}                     // required to read     public TimeStamp(int hour, int second){       this.hour = hour;       this.second = second;     }   }    public static void main(String[] args) throws Exception {     // one argument: a file name     File file = new File(args[0]);      // get the reflected schema for packets     Schema schema = ReflectData.get().getSchema(Packet.class);      // create a file of packets     DatumWriter<Packet> writer = new ReflectDatumWriter<Packet>(Packet.class);     DataFileWriter<Packet> out = new DataFileWriter<Packet>(writer)       .setCodec(CodecFactory.deflateCodec(9))       .create(schema, file);      // write 100 packets to the file, odds with null timestamp     for (int i = 0; i < 100; i++) {       out.append(new Packet(i, (i%2==0) ? new TimeStamp(12, i) : null));     }      // close the output file     out.close();      // open a file of packets     DatumReader<Packet> reader = new ReflectDatumReader<Packet>(Packet.class);     DataFileReader<Packet> in = new DataFileReader<Packet>(file, reader);      // read 100 packets from the file & print them as JSON     for (Packet packet : in) {       System.out.println(ReflectData.get().toString(packet));     }      // close the input file     in.close();   }  }