Building scalable network applications with Netty (as presented on NLJUG JFall 2013)

Building scalable network applications with Netty

Jaap ter Woerds@jaaptw

XMS pin: EBDDFF9A

The trouble with synchronous IO

The trouble with synchronous IO

The trouble with synchronous IO

Creating your custom server

Creating your custom server

Netty?

Unified, asynchronous programming model. All IO operations return immediately.

Netty?

Channel channel =..channel.write(myMsg).addListener(new ChannelFutureListener() { @Override public void operationComplete(ChannelFuture future) throws Exception { if(future.isSuccess()){ // Business as usual } else{ // Handle failure } }});

Netty?

Networking application framework with a modular architecture and quite some ready reusable

components.

When should I care about this?

Custom servers / networking applications / proxies

High concurrency

Netty concepts

Netty concepts

ByteBuf random accessable sequence of bytes

Abstraction over plain byte arrays and NIO buffers

Netty concepts

ByteBuf Use: encoding and decoding data

ByteBuf b = .b.writeInt(3).writeBoolean(true);

Netty concepts

Channel Link ('connection') to a resource that provides IO operations like read /

write

Netty concepts

ChannelChannel c = ..;

c.write(myMsg).addListener(CLOSE);

Netty concepts

ChannelHandler IO event listener,handles outbound and / or inbound events.

Netty concepts

ChannelInboundHandler Defines listener methods for incoming IO events

Netty concepts

ChannelInboundHandler

channelActive(ChannelHandlerContext ctx)channelRead(ChannelHandlerContext ctx, Object msg)

channelReadComplete(ChannelHandlerContext ctx)channelInactive(ChannelHandlerContext ctx)

....

Netty concepts

ChannelOutboundHandler Defines listener methods for outgoing IO events

Netty concepts

ChannelOutboundHandler

write(ChannelHandlerContext ctx, Object msg, ChannelPromise..)flush(ChannelHandlerContext ctx)

Netty concepts

ChannelPipelineA List of ChannelHandlers that process incoming and outgoing events

in a specific order

Netty concepts

ChannelInitializerConfigures the pipeline for a Channel. In fact, a special case of

ChannelInboundHandler which creates the handlers for a channel whenerver a new channel is registered.

Netty concepts

ChannelInitializerConfigures the pipeline for a Channel. In fact, a special case of

ChannelInboundHandler which creates the handlers for a channel whenerver a new channel is registered.

Netty concepts

ChannelInitializer @Override public void initChannel(SocketChannel ch) throws Exception { ChannelPipeline pipeline = ch.pipeline(); // Decoders pipeline.addLast("frameDecoder", new LineBasedFrameDecoder(MAX_LENGTH)); pipeline.addLast("stringDecoder", STRING_DECODER); pipeline.addLast("moderatorHandler", moderatorHandler); pipeline.addLast("chatServerHandler", chatServerHandler); // Encoder pipeline.addLast("stringEncoder", STRING_ENCODER); }

Netty concepts

Bootstrap

EventLoopGroup bossGroup = new NioEventLoopGroup();EventLoopGroup workerGroup = new NioEventLoopGroup();ServerBootstrap b = new ServerBootstrap();b.group(bossGroup, workerGroup) .channel(NioServerSocketChannel.class) .option(ChannelOption.SO_BACKLOG, BACKLOG) .handler(new LoggingHandler(LogLevel.INFO)) .childHandler(channelInitializer);ChannelFuture f = b.bind(port).sync();f.channel().closeFuture().sync();

Netty architecture

Chain of responsibilityIncoming data flow through the ChannelPipeline

- Framing ByteBuf- Decode frames

- Decode frames in DTOs/POJOs

Netty architecture

Netty components

Out of the box support for:Streaming compression Zlib

SSL stream encryptionHTTP

WebSocketsProtocolBuffer

XMS server protocol layer

Example SSE / CORS

Example SSE / CORS

In the last handler we deal with normal POJO and handle an incoming request without actually caring about the connection layer!

@Overridepublic void channelRead(ChannelHandlerContext ctx, Object msg) { IncomingMessagePojo m = (IncomingMessagePojo) msg; handle(m);// Login / Send a text message/ Handle create group}

Example SSE / CORS

Thank you!

Example code:https://github.com/jaapterwoerds/jfall-netty4

Further reading:

https://nettio.io

http://xms.mehttp://tech.ebuddy.com