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:

Netty

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
   {
       @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 );
               String out = in.toUpperCase(); // Shout!
               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

Originally posted at 2016-09-15 14:56:10+00:00. Automatically generated from the original post : apologies for the errors introduced.

original post

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