使用apache avro反映

Avro序列化在Hadoop用户中很受欢迎，但很难找到示例。

有谁能帮我这个示例代码？ 我最感兴趣的是使用Reflect API来读/写文件并使用Union和Null注释。

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

这是上述程序的一个版本。

这也使用压缩文件。

 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 writer = new ReflectDatumWriter(Packet.class); DataFileWriter out = new DataFileWriter(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 reader = new ReflectDatumReader(Packet.class); DataFileReader in = new DataFileReader(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(); } } 

Answer 2

请参阅https://sites.google.com/site/developertips/Home/java/apache-avro上的示例3.它展示了如何使用reflectionAPI编写和读取Java类。