Apache Avro 是一个序列化系统，提供如下功能：
1.丰富的数据结构
2.压缩的、快速的、二进制数据格式
3.存储持久化数据的容器文件
4.RPC功能
5.可以简单实现与动态语言的集成
特点：
Avro在数据读写过程中都利用基于JSON格式的Schemas，因而不用在序列化时对每个数据都要加一个类型等头部信息，从而使序列化保持快而小。并且因为数据加上对应的schema是自描述的，这样也可以促进在动态、脚本语言中的使用。
二、示例
示例参考【 https://github.com/phunt/avro-rpc-quickstart】
本示例利用Mail协议简单模拟一个远程服务，Avro将利用这个服务来发送消息
1.编辑avpr协议文件
{"namespace": "example.proto", （1）
"protocol": "Mail", （2）
"types": [ （3）
{"name": "Message", "type": "record",
"fields": [
{"name": "to", "type": "string"},
{"name": "from", "type": "string"},
{"name": "body", "type": "string"}
]
}
],
"messages": { （4）
"send": {
"request": [{"name": "message", "type": "Message"}],
"response": "string"
}
}
}
（1）定义命名空间
（2）定义协议名称
（3）定义类型信息
（4）定义rpc Messages
2.编写pom文件
4.0.0 example.qs avro-rpc-quickstart jar 1.8.1-SNAPSHOT avro-rpc-quickstart http://maven.apache.org UTF-8 3.5 1.8.1 junit junit 4.10 test org.slf4j slf4j-simple 1.6.4 compile org.apache.avro avro ${avro.version} org.apache.avro avro-ipc ${avro.version} org.apache.maven.plugins maven-compiler-plugin ${compiler-plugin.version} org.apache.avro avro-maven-plugin ${avro.version} schemas generate-sources schema protocol idl-protocol ${project.basedir}/src/main/avro/ ${project.basedir}/src/main/java/
3.在项目目录下执行 mvn compile ，执行结束后生成 Mail.java 和Message.java文件
4.编写测试程序
/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package example;
import java.io.IOException;
import java.net.InetSocketAddress;
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 example.proto.Mail;
import example.proto.Message;
/**
* Start a server, attach a client, and send a message.
*/
public class Main {
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: ");
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();
}
}
5.执行测试，出入参数 tianjin beijing hello
执行结果
Client built, got proxy
Calling proxy.send with message: {"to": "tianjin", "from": "beijing", "body": "hello"}
Sending message
Result: Sending message to tianjin from beijing with body hello
6.工程代码参考附件
* 当数据类型是 Map
默认情况下，avpr文件中数据类型是string时，利用avro-maven-plugin生成的数据类型是CharSequence，比如：
{"namespace": "example.proto",
"protocol": "Mail",
"messages": {
"send": {
"request": [{"name": "jobId", "type": "string"},{"name": "message", "type": {"type":"map","values":"string"}}],
"response": "string"
}
}
}
默认生成的类文件：
/**
* Autogenerated by Avro
*
* DO NOT EDIT DIRECTLY
*/
package example.proto;
@SuppressWarnings("all")
@org.apache.avro.specific.AvroGenerated
public interface Mail {
public static final org.apache.avro.Protocol PROTOCOL = org.apache.avro.Protocol.parse("{\"protocol\":\"Mail\",\"namespace\":\"example.proto\",\"types\":[],\"messages\":{\"send\":{\"request\":[{\"name\":\"jobId\",\"type\":\"string\"},{\"name\":\"message\",\"type\":{\"type\":\"map\",\"values\":\"string\"}}],\"response\":\"string\"}}}");
/**
*/
java.lang.CharSequence send(java.lang.CharSequence jobId, java.util.Map message) throws org.apache.avro.AvroRemoteException;
@SuppressWarnings("all")
public interface Callback extends Mail {
public static final org.apache.avro.Protocol PROTOCOL = example.proto.Mail.PROTOCOL;
/**
* @throws java.io.IOException The async call could not be completed.
*/
void send(java.lang.CharSequence jobId, java.util.Map message, org.apache.avro.ipc.Callback callback) throws java.io.IOException;
}
}
如果我们想在程序中使用String类型时，需要在avro-maven-plugin 中加入
org.apache.avro avro-maven-plugin ${avro.version} String
此时生成的Java文件
/**
* Autogenerated by Avro
*
* DO NOT EDIT DIRECTLY
*/
package example.proto;
@SuppressWarnings("all")
@org.apache.avro.specific.AvroGenerated
public interface Mail {
public static final org.apache.avro.Protocol PROTOCOL = org.apache.avro.Protocol.parse("{\"protocol\":\"Mail\",\"namespace\":\"example.proto\",\"types\":[],\"messages\":{\"send\":{\"request\":[{\"name\":\"jobId\",\"type\":{\"type\":\"string\",\"avro.java.string\":\"String\"}},{\"name\":\"message\",\"type\":{\"type\":\"map\",\"values\":{\"type\":\"string\",\"avro.java.string\":\"String\"},\"avro.java.string\":\"String\"}}],\"response\":{\"type\":\"string\",\"avro.java.string\":\"String\"}}}}");
/**
*/
java.lang.String send(java.lang.String jobId, java.util.Map message) throws org.apache.avro.AvroRemoteException;
@SuppressWarnings("all")
public interface Callback extends Mail {
public static final org.apache.avro.Protocol PROTOCOL = example.proto.Mail.PROTOCOL;
/**
* @throws java.io.IOException The async call could not be completed.
*/
void send(java.lang.String jobId, java.util.Map message, org.apache.avro.ipc.Callback callback) throws java.io.IOException;
}
}