Simple example of Netty 4 usage

I feel the title of this post over-promises, since I was not able to make an example that seemed simple to me.

Anyway, here is a near-minimal example of how to use Netty to make a server that shouts back at you whatever you say:

NettyExample.java:

import io.netty.bootstrap.ServerBootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.channel.socket.SocketChannel;
import io.netty.util.CharsetUtil;
import io.netty.util.ReferenceCountUtil;
import java.nio.charset.Charset;

class NettyExample
{
public static void main( String[] args ) throws Exception
{
EventLoopGroup bossGroup = new NioEventLoopGroup();
EventLoopGroup workerGroup = new NioEventLoopGroup();
try
{
new ServerBootstrap()
.group( bossGroup, workerGroup )
.channel( NioServerSocketChannel.class )
.childHandler( new Init() )
.bind( 1337 ).sync().channel().closeFuture().sync();
}
finally
{
bossGroup.shutdownGracefully();
workerGroup.shutdownGracefully();
}
}
private static class Init extends ChannelInitializer<socketchannel>
{
    @Override
    public void
    initChannel( SocketChannel ch ) throws Exception
    {
        ch.pipeline().addLast( new ShoutyHandler() );
    }
}

private static class ShoutyHandler extends ChannelInboundHandlerAdapter
{
    @Override
    public void channelRead( ChannelHandlerContext ctx, Object msg )
    {
        try
        {
            Charset utf8 = CharsetUtil.UTF_8;
            String in = ( (ByteBuf)msg ).toString( utf8 );
            <span style="color:red;">String out = in.toUpperCase(); // Shout!</span>
            ctx.writeAndFlush( Unpooled.copiedBuffer( out, utf8 ) );
        }
        finally
        {
            ReferenceCountUtil.release( msg );
        }
    }

    @Override
    public void exceptionCaught(
        ChannelHandlerContext ctx, Throwable cause )
    {
        cause.printStackTrace();
        ctx.close();
    }
}

}

The lines that actually do something useful are highlighted in red. If anyone knows how to make it shorter, please comment below. It seems a lot to me.

To run this, do:

sudo apt-get install openjdk-8-jdk
wget 'http://search.maven.org/remotecontent?filepath=io/netty/netty-all/4.1.5.Final/netty-all-4.1.5.Final.jar -O netty-all-4.1.5.Final.jar'
javac -Werror -cp netty-all-4.1.5.Final.jar:. NettyExample.java && java -cp netty-all-4.1.5.Final.jar:. NettyExample

Then in another terminal:

echo "Hello, world" | nc localhost 1337

and observe the response:

HELLO, WORLD

Comparison with Node.js

Just for comparison, here is an approximate equivalent in Node.js:

shouty.js:

var net = require('net');

var server = net.createServer(
function( socket ) {
socket.setEncoding('utf8');
socket.on(
'data',
function( data ) {
socket.end( data.toUpperCase() );
}
)
}
);
server.listen( 1337, "localhost" );

To run it, do:

sudo apt-get install nodejs-legacy
node shouty.js

Then in another terminal:

echo "Hello, world" | nc localhost 1337

and observe the response:

HELLO, WORLD