这是上述程序的有效版本。
这也对文件使用压缩。
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(); }}
