关于avro序列化

      Avro提供了两种序列化的方式：

      avro-specific:

      和thrift一样可以通过idl方式生成代码,生成命令:

java -jar avro-tools-1.7.4.jar compile schema data.avsc src/

      avro-generic:

     支持schema的动态加载,不需要重新编译就可以处理新的数据源

      avro的数据类型:

      基本类型:

      null:                     no value

      boolean:              a binary value

      int:                       32-bit signed integer

      long:                    64-bit signed integer

      float:                    single precision (32-bit) IEEE 754 floating-point number

      double:                double precision (64-bit) IEEE 754 floating-point number

      bytes:                  sequence of 8-bit unsigned bytes

      string:                  unicode character sequence

      复杂类型:

      avro支持6种复杂类型：records, enums, arrays, maps, unionsm, fixed

       下面是一个定义为records例子：

       {

       "type": "record",                                      // 指定record类型,(required)

        "name": "AvroData",                               // 生成的类名称,(required)

        "namespace": "com.wuwen.",                 // 命令空间,(optional)

        "doc": "avro scheama test.",                  // 用来描述该schema的,(optional)

        "aliases": ["avroaliases"],                       // name的别名,(optional)

        "fields": [                                                // 字段名,(required)

               {"name": "GUID", "type": "string"},   // 定义一个字段名为GUID，基本数据类型为string的字段

               {"name": "Content", "type": "string"},

               {"name": "Time", "type": "long"}

        ]

        }

         例子:

package com.wuwen;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.IOException;

import org.apache.avro.Schema;
import org.apache.avro.file.DataFileReader;
import org.apache.avro.file.DataFileWriter;
import org.apache.avro.file.FileReader;
import org.apache.avro.generic.GenericData;
import org.apache.avro.generic.GenericDatumReader;
import org.apache.avro.generic.GenericDatumWriter;
import org.apache.avro.generic.GenericRecord;
import org.apache.avro.io.BinaryDecoder;
import org.apache.avro.io.DatumReader;
import org.apache.avro.io.DatumWriter;
import org.apache.avro.io.DecoderFactory;
import org.apache.avro.io.Encoder;
import org.apache.avro.io.EncoderFactory;
import org.apache.avro.specific.SpecificDatumReader;
import org.apache.avro.specific.SpecificDatumWriter;
import org.apache.avro.util.Utf8;

public class AvroDemo {

	public void serializeGeneric() throws IOException {
		Schema schema = Schema.parse(new File("E:/avro/AvroData.avsc"));
		GenericRecord datum = new GenericData.Record(schema);
		datum.put("GUID", new Utf8("1234567"));
		datum.put("Content", new Utf8("Avro测试"));
		datum.put("Time", 20130305134700L);

		// Serialize it.
		ByteArrayOutputStream out = new ByteArrayOutputStream();
		DatumWriter<GenericRecord> writer = new GenericDatumWriter<GenericRecord>(schema);
		Encoder encoder = EncoderFactory.get().binaryEncoder(out, null);
		writer.write(datum, encoder);
		encoder.flush();
		out.close();

		// Deserialize it.
		DatumReader<GenericRecord> reader = new GenericDatumReader<GenericRecord>(schema);
		BinaryDecoder decoder = DecoderFactory.get().binaryDecoder(out.toByteArray(), null);
		GenericRecord result = reader.read(null, decoder);
		System.out.printf("GUID: %s, Content: %s, Time: %s\n", result.get("GUID"), result.get("Content"), result.get("Time"));
	}

	public void serializeSpecific() throws IOException {
		AvroData datum = new AvroData();
		datum.setGUID(new Utf8("1234567"));
		datum.setContent(new Utf8("1234567"));
		datum.setTime(20130305134700L);

		File tmpFile = new File("E:/avro/myAvroExample.avro");
		// Serialize it.
		DataFileWriter<AvroData> writer = new DataFileWriter<AvroData>(new SpecificDatumWriter<AvroData>(AvroData.class));
		writer.create(AvroData.SCHEMA$, tmpFile);
		writer.append(datum);
		writer.close();

		// Deserialize it.
		FileReader<AvroData> reader = DataFileReader.openReader(tmpFile, new SpecificDatumReader<AvroData>(AvroData.class));
		while (reader.hasNext()) {
			AvroData result = reader.next();
			System.out.printf("GUID: %s, Content: %s, Time: %s\n", result.getGUID(), result.getContent(), result.getTime());
		}
		reader.close();
	}

	public static void main(String[] args) throws IOException {
		AvroDemo example = new AvroDemo();
		System.out.println("Generic");
		example.serializeGeneric();
		System.out.println("Specific");
		example.serializeSpecific();
	}
}