Protocol Buffers介绍
Protocol Buffers（Protobuf）是Google推出的语言无关，平台无关的可扩展机制，用于序列化结构数据。由于是一种二进制的序列化协议，并且数据结构做了相应优化，因此比传统的XML、JSON数据格式序列化后体积更小，传输更快。Protobuf有proto2和proto3两个版本，有着不同的数据格式定义，在这里我们使用proto3版本。Protobuf使用了一个编译器，可根据.proto文件中定义的数据结构，自动生成各种语言的模板代码，方便使用。
一个hello world示例程序
我们以一个hello world的例子来尝试在Netty中使用Protobuf：编写一个GreetClient，向服务端发送用户姓名name（如world）；服务端接收到请求，在姓名name前面添加前缀hello（如name为hello，添加前缀变为hello word），并将该消息message返回给客户端。这个例子参考了grpc官方的hello world例子。
编写helloworld.proto文件
首先我们编写一个helloworld.proto文件，内容如下：
syntax = "proto3";
option java_multiple_files = true;
option java_package = "com.alphabc.netty.protobuf.helloworld";
option java_outer_classname = "HelloWorldProto";
option objc_class_prefix = "HLW";
package helloworld;
// The request message containing the user's name.
message HelloRequest {
string name = 1;
}
// The response message containing the greetings
message HelloReply {
string message = 1;
}
编译生成Java代码
从Protobuf的官方github release页面下载对应操作系统上需要用到的编译器文件，并解压得到protoc。
为了使用protoc将helloworld.proto文件编译成Java代码，进入项目目录执行以下命令：
protoc --java_out=src/main/java src/main/java/com/alphabc/netty/protobuf/helloworld/helloworld.proto
最终生成的类目录结构大致如下：
src/main/java/com/alphabc/netty/protobuf/helloworld
├── HelloReply.java
├── HelloReplyOrBuilder.java
├── HelloRequest.java
├── HelloRequestOrBuilder.java
├── HelloWorldProto.java
└── helloworld.proto
由于生成的模板代码较多，此处就不贴出来了。
引入Maven依赖
引入Netty和Protobuf的Maven依赖如下：
io.netty
netty-all
4.1.32.Final
com.google.protobuf
protobuf-java
3.11.0
测试Protobuf的序列化和反序列化
编写Protobuf的序列化和反序列化测试类如下：
package com.alphabc.netty.protobuf;
import com.alphabc.netty.protobuf.helloworld.HelloRequest;
import com.google.protobuf.InvalidProtocolBufferException;
public class ProtobufTest {
public static void main(String[] args) throws InvalidProtocolBufferException {
HelloRequest helloRequest = HelloRequest.newBuilder().setName("Jack").build();
byte[] bytes = helloRequest.toByteArray();
HelloRequest parse = HelloRequest.parseFrom(bytes);
System.out.println(parse.toString());
System.out.println(parse.getName());
}
}
执行后控制台输出：
name: "Jack"
Jack
编写服务端和客户端代码
编写Netty服务端GreetServer代码：
package com.alphabc.netty.protobuf;
import com.alphabc.netty.protobuf.helloworld.HelloRequest;
import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.codec.protobuf.ProtobufDecoder;
import io.netty.handler.codec.protobuf.ProtobufEncoder;
import io.netty.handler.codec.protobuf.ProtobufVarint32FrameDecoder;
import io.netty.handler.codec.protobuf.ProtobufVarint32LengthFieldPrepender;
import java.net.InetSocketAddress;
public class GreetServer {
private final int port;
public GreetServer(int port) {
this.port = port;
}
public static void main(String[] args) throws Exception {
if (args.length != 1) {
System.err.println("Usage: " + GreetServer.class.getSimpleName() + " ");
return;
}
int port = Integer.parseInt(args[0]);
new GreetServer(port).start();
}
public void start() throws Exception {
NioEventLoopGroup bossGroup = new NioEventLoopGroup();
NioEventLoopGroup workerGroup = new NioEventLoopGroup();
try {
ServerBootstrap b = new ServerBootstrap();
b.group(bossGroup, workerGroup)
.channel(NioServerSocketChannel.class)
.localAddress(new InetSocketAddress(port))
.childHandler(new ChannelInitializer() {
@Override
public void initChannel(SocketChannel ch) {
ch.pipeline().addLast(new ProtobufVarint32FrameDecoder())
.addLast(new ProtobufDecoder(HelloRequest.getDefaultInstance()))
.addLast(new ProtobufVarint32LengthFieldPrepender())
.addLast(new ProtobufEncoder())
.addLast(new GreetServerHandler());
}
});
ChannelFuture f = b.bind().sync();
System.out.println(GreetServer.class.getName() + " started and listen on " + f.channel().localAddress());
f.channel().closeFuture().sync();
} finally {
bossGroup.shutdownGracefully().sync();
workerGroup.shutdownGracefully().sync();
}
}
}
服务端处理器GreetServerHandler代码如下：
package com.alphabc.netty.protobuf;
import com.alphabc.netty.protobuf.helloworld.HelloReply;
import com.alphabc.netty.protobuf.helloworld.HelloRequest;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
public class GreetServerHandler extends SimpleChannelInboundHandler {
@Override
protected void channelRead0(ChannelHandlerContext ctx, HelloRequest msg) throws Exception {
System.out.println("request: " + msg.getName());
HelloReply reply = HelloReply.newBuilder().setMessage("Hello " + msg.getName()).build();
ChannelFuture future = ctx.writeAndFlush(reply);
future.addListener(ChannelFutureListener.CLOSE);
}
}
Netty客户端代码：
package com.alphabc.netty.protobuf;
import com.alphabc.netty.protobuf.helloworld.HelloReply;
import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.protobuf.ProtobufDecoder;
import io.netty.handler.codec.protobuf.ProtobufEncoder;
import io.netty.handler.codec.protobuf.ProtobufVarint32FrameDecoder;
import io.netty.handler.codec.protobuf.ProtobufVarint32LengthFieldPrepender;
import java.net.InetSocketAddress;
public class GreetClient {
private final String host;
private final int port;
public GreetClient(String host, int port) {
this.host = host;
this.port = port;
}
public static void main(String[] args) throws Exception {
if (args.length != 2) {
System.err.println("Usage: " + GreetClient.class.getSimpleName() + " ");
return;
}
final String host = args[0];
final int port = Integer.parseInt(args[1]);
new GreetClient(host, port).start();
}
private void start() throws Exception {
EventLoopGroup group = new NioEventLoopGroup();
try {
Bootstrap b = new Bootstrap();
b.group(group)
.channel(NioSocketChannel.class)
.remoteAddress(new InetSocketAddress(host, port))
.handler(new ChannelInitializer() {
@Override
public void initChannel(SocketChannel ch) {
ch.pipeline().addLast(new ProtobufVarint32FrameDecoder())
.addLast(new ProtobufDecoder(HelloReply.getDefaultInstance()))
.addLast(new ProtobufVarint32LengthFieldPrepender())
.addLast(new ProtobufEncoder())
.addLast(new GreetClientHandler());
}
});
ChannelFuture f = b.connect().sync();
f.channel().closeFuture().sync();
} finally {
group.shutdownGracefully().sync();
}
}
}
客户端处理器GreetClientHandler：
package com.alphabc.netty.protobuf;
import com.alphabc.netty.protobuf.helloworld.HelloReply;
import com.alphabc.netty.protobuf.helloworld.HelloRequest;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
public class GreetClientHandler extends SimpleChannelInboundHandler {
@Override
protected void channelRead0(ChannelHandlerContext ctx, HelloReply msg) throws Exception {
System.out.println("Greeting: " + msg.getMessage());
}
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
HelloRequest request = HelloRequest.newBuilder().setName("world").build();
ctx.writeAndFlush(request);
}
}
代码测试
首先启动服务端，监听于5000端口，再启动客户端进行测试。
服务端控制台输出如下：
com.alphabc.netty.protobuf.GreetServer started and listen on /0:0:0:0:0:0:0:0:5000
request: world
客户端控制台输出如下：
Greeting: Hello world
总结
从hello world示例程序可以看出，Netty已经为我们内置相应的Protobuf编解码器，编写一个使用Protobuf协议的服务端和客户端还是相对简单的，但是要写好还是有很多事情要处理，如异常处理和支持多个Protobuf消息等等问题。
参考资料
- GitHub - protocolbuffers/protobuf: Protocol Buffers - Google's data interchange format
- Protocol Buffers | Google Developers
- Language Guide (proto3) | Protocol Buffers | Google Developers
- Protocol Buffer Basics: Java | Protocol Buffers | Google Developers
- grpc-java/examples/src/main/java/io/grpc/examples/helloworld at master · grpc/grpc-java