avro實現序列化以及RPC的簡單示例

看到不少在提到hadoop的同時，都會提到avro和thrift兩個數據持久化(序列化)的項目。特別是avro，Doug Cutting 又是creator.  apache官方的序列化的示例有提供java版本和python版本的，都是很是簡單的示例，結合maven很是容易上手，可是關於RPC的示例則顯得比較簡單，摸索了半天，這裏做個備忘。

首先是pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>avro-sample</groupId>
    <artifactId>avro-sample</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <dependency>
            <groupId>org.apache.avro</groupId>
            <artifactId>avro</artifactId>
            <version>1.7.5</version>
        </dependency>
        <dependency>
            <groupId>org.apache.avro</groupId>
            <artifactId>avro-ipc</artifactId>
            <version>1.7.5</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.avro</groupId>
                <artifactId>avro-maven-plugin</artifactId>
                <version>1.7.5</version>
                <executions>
                    <execution>
                        <id>schemas</id>
                        <phase>generate-sources</phase>
                        <goals>
                            <goal>schema</goal>
                            <goal>protocol</goal>
                            <goal>idl-protocol</goal>
                        </goals>
                        <configuration>
                            <sourceDirectory>${project.basedir}/src/main/resources/</sourceDirectory>
                            <outputDirectory>${project.basedir}/src/main/java/</outputDirectory>
                            <testSourceDirectory>${project.basedir}/src/test/resources/</testSourceDirectory>
                            <testOutputDirectory>${project.basedir}/src/test/java/</testOutputDirectory>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>1.6</source>
                    <target>1.6</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

注意其中設置了插件，用於代碼自動生成的，將user.avsc和mail.avpr放到main/resources/目錄下, 而後能夠運行mvn generate-sources,  相關的protocol等類就自動生成了

user.avsc

{"namespace": "example.avro",
 "type": "record",
 "name": "User",
 "fields": [
     {"name": "name", "type": "string"},
     {"name": "favorite_number",  "type": ["int", "null"]},
     {"name": "favorite_color", "type": ["string", "null"]}
 ]
}

mail.avpr

{"namespace": "example.proto",
 "protocol": "Mail",

 "types": [
     {"name": "Message", "type": "record",
      "fields": [
          {"name": "to",   "type": "string"},
          {"name": "from", "type": "string"},
          {"name": "body", "type": "string"}
      ]
     }
 ],
 "messages": {
     "send": {
         "request": [{"name": "message", "type": "Message"}],
         "response": "string"
     }
 }
}

RPCMain.java

package example.avro;

import java.io.IOException;
import java.net.InetSocketAddress;

import org.apache.avro.ipc.SocketServer;
import org.apache.avro.ipc.SocketTransceiver;
import org.apache.avro.ipc.specific.SpecificRequestor;
import org.apache.avro.ipc.specific.SpecificResponder;
import org.apache.avro.util.Utf8;

import example.proto.Mail;
import example.proto.Message;
import org.apache.avro.ipc.NettyServer;
import org.apache.avro.ipc.NettyTransceiver;
import org.apache.avro.ipc.Server;
import org.apache.avro.ipc.specific.SpecificRequestor;
import org.apache.avro.ipc.specific.SpecificResponder;
import org.apache.avro.util.Utf8;

import java.io.IOException;
import java.net.InetSocketAddress;


public class RPCMain {
    public static class MailImpl implements Mail {
        // in this simple example just return details of the message
        public Utf8 send(Message message) {
            System.out.println("Sending message");
            return new Utf8("Sending message to " + message.getTo().toString()
                    + " from " + message.getFrom().toString()
                    + " with body " + message.getBody().toString());
        }
    }

    private static Server server;

    private static void startServer() throws IOException {
        server = new NettyServer(new SpecificResponder(Mail.class, new MailImpl()), new InetSocketAddress(65111));
        // the server implements the Mail protocol (MailImpl)
    }

    public static void main(String[] args) throws IOException {
        if (args.length != 3) {
            System.out.println("Usage: <to> <from> <body>");
            System.exit(1);
        }

        System.out.println("Starting server");
        // usually this would be another app, but for simplicity
        startServer();
        System.out.println("Server started");

        NettyTransceiver client = new NettyTransceiver(new InetSocketAddress(65111));
        // client code - attach to the server and send a message
        Mail proxy = (Mail) SpecificRequestor.getClient(Mail.class, client);
        System.out.println("Client built, got proxy");

        // fill in the Message record and send it
        Message message = new Message();
        message.setTo(new Utf8(args[0]));
        message.setFrom(new Utf8(args[1]));
        message.setBody(new Utf8(args[2]));
        System.out.println("Calling proxy.send with message:  " + message.toString());
        System.out.println("Result: " + proxy.send(message));

        // cleanup
        client.close();
        server.close();
    }
}

SpecificMain.java能夠參考官方示例

package example.avro;

import org.apache.avro.file.DataFileReader;
import org.apache.avro.file.DataFileWriter;
import org.apache.avro.generic.GenericDatumReader;
import org.apache.avro.generic.GenericRecord;
import org.apache.avro.io.DatumReader;
import org.apache.avro.io.DatumWriter;
import org.apache.avro.specific.SpecificDatumWriter;

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


public class SpecificMain {

    public static void main(String args[]) throws IOException {
        User user1 = new User();
        user1.setName("Alyssa");
        user1.setFavoriteNumber(256);
        // Leave favorite color null

        // Alternate constructor
        User user2 = new User("Ben", 7, "red");

        // Construct via builder
        User user3 = User.newBuilder()
                .setName("Charlie")
                .setFavoriteColor("blue")
                .setFavoriteNumber(null)
                .build();


        // Serialize user1 and user2 to disk
        DatumWriter<User> userDatumWriter = new SpecificDatumWriter<User>(User.class);
        DataFileWriter<User> dataFileWriter = new DataFileWriter<User>(userDatumWriter);

        File file = new File("users.avro");
        System.out.println(file.getAbsolutePath());

        dataFileWriter.create(user1.getSchema(), file);
        dataFileWriter.append(user1);
        dataFileWriter.append(user2);
        dataFileWriter.append(user3);
        dataFileWriter.close();


        // Deserialize users from disk
        DatumReader<GenericRecord> datumReader = new GenericDatumReader<GenericRecord>(user1.getSchema());
        DataFileReader<GenericRecord> dataFileReader = new DataFileReader<GenericRecord>(file, datumReader);
        GenericRecord user = null;
        while (dataFileReader.hasNext()) {
            // Reuse user object by passing it to next(). This saves us from
            // allocating and garbage collecting many objects for files with
            // many items.
            user = dataFileReader.next(user);
            System.out.println(user);
        }
    }
}

此外我下載了avro的python包，而後用python讀了一下用java生成的user.avro文件

SpecificMain.py

import avro.schema
from avro.datafile import DataFileReader, DataFileWriter
from avro.io import DatumReader, DatumWriter
reader = DataFileReader(open("users.avro", "r"), DatumReader())
for user in reader:
    print user
reader.close()