Integrating Protobuf with Netty for Java Object Transmission

The article demonstrates how to use Netty socket programming together with Google Protobuf to serialize and transmit Java objects between a server and a client.

First, a Person.proto file is created under a protobuf directory with the following content:

syntax = "proto3";
package com.badao.protobuf;
option optimize_for = SPEED;
option java_package = "com.badao.NettyProtobuf";
option java_outer_classname = "BadaoDataInfo";

message Person {
  string name = 1;
  int32 age = 2;
  string address = 3;
}

The protoc compiler is then invoked to generate Java classes:

protoc --java_out=src/main/java src/protobuf/Person.proto

This produces BadaoDataInfo.Person in the com.badao.NettyProtobuf package.

Next, a Netty server is implemented. The NettyProtobufServer class creates boss and worker EventLoopGroup s, configures a ServerBootstrap, adds the custom initializer NettyProtobufInitializer, binds to port 70, and shuts down gracefully:

package com.badao.NettyProtobuf;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;

public class NettyProtobufServer {
    public static void main(String[] args) throws Exception {
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            ServerBootstrap serverBootstrap = new ServerBootstrap();
            serverBootstrap.group(bossGroup, workerGroup)
                .channel(NioServerSocketChannel.class)
                .handler(new LoggingHandler(LogLevel.INFO))
                .childHandler(new NettyProtobufInitializer());
            ChannelFuture channelFuture = serverBootstrap.bind(70).sync();
            channelFuture.channel().closeFuture().sync();
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}

The initializer configures the channel pipeline with Netty's built‑in Protobuf handlers and a custom handler:

package com.badao.NettyProtobuf;

import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.socket.SocketChannel;
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;

public class NettyProtobufInitializer extends ChannelInitializer<SocketChannel> {
    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        ChannelPipeline pipeline = ch.pipeline();
        pipeline.addLast(new ProtobufVarint32FrameDecoder());
        pipeline.addLast(new ProtobufDecoder(BadaoDataInfo.Person.getDefaultInstance()));
        pipeline.addLast(new ProtobufVarint32LengthFieldPrepender());
        pipeline.addLast(new ProtobufEncoder());
        pipeline.addLast(new NettyProtobufHandler());
    }
}

The custom handler simply prints the received Person fields:

package com.badao.NettyProtobuf;

import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;

public class NettyProtobufHandler extends SimpleChannelInboundHandler<BadaoDataInfo.Person> {
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, BadaoDataInfo.Person msg) throws Exception {
        System.out.println(msg.getName());
        System.out.println(msg.getAge());
        System.out.println(msg.getAddress());
    }
}

On the client side, NettyProtobufClient sets up a Bootstrap, connects to localhost:70, and uses a matching initializer:

package com.badao.NettyProtobuf;

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioSocketChannel;

public class NettyProtobufClient {
    public static void main(String[] args) throws Exception {
        EventLoopGroup eventLoopGroup = new NioEventLoopGroup();
        try {
            Bootstrap bootstrap = new Bootstrap();
            bootstrap.group(eventLoopGroup)
                .channel(NioSocketChannel.class)
                .handler(new NettyProtoBufClientInitializer());
            ChannelFuture channelFuture = bootstrap.connect("localhost", 70);
            channelFuture.channel().closeFuture().sync();
        } finally {
            eventLoopGroup.shutdownGracefully();
        }
    }
}

The client initializer mirrors the server pipeline:

package com.badao.NettyProtobuf;

import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.socket.SocketChannel;
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;

public class NettyProtoBufClientInitializer extends ChannelInitializer<SocketChannel> {
    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        ChannelPipeline pipeline = ch.pipeline();
        pipeline.addLast(new ProtobufVarint32FrameDecoder());
        pipeline.addLast(new ProtobufDecoder(BadaoDataInfo.Person.getDefaultInstance()));
        pipeline.addLast(new ProtobufVarint32LengthFieldPrepender());
        pipeline.addLast(new ProtobufEncoder());
        pipeline.addLast(new NettyProtobufClientHandler());
    }
}

The client handler builds a Person message when the channel becomes active and sends it to the server:

package com.badao.NettyProtobuf;

import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;

public class NettyProtobufClientHandler extends SimpleChannelInboundHandler<BadaoDataInfo.Person> {
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, BadaoDataInfo.Person msg) throws Exception {
        // No processing needed for this demo
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        BadaoDataInfo.Person person = BadaoDataInfo.Person.newBuilder()
                .setName("公众号:霸道的程序猿")
                .setAge(100)
                .setAddress("中国")
                .build();
        ctx.channel().writeAndFlush(person);
    }
}

Running the server's main method followed by the client's main method establishes a TCP connection, transmits the serialized Person object, and the server prints the name, age, and address. The article also provides a screenshot of the console output and a download link for the complete example code.