Building Netty Servers

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This presentation on building servers explains what is Netty, why choosing it and shows how with very little code you can build an asynchronous app server.

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Building Netty Servers

  1. 1. Building Netty Servers Dani Solà
  2. 2. What is Netty? Asynchronous event-driven networkapplication framework for rapid development of maintainable high performance protocol servers & clients
  3. 3. Meaning...● A set of abstractions to build your server with: – Good performance – Low resource consumption – Unified API for various transport types – Customizable thread model – Good documentation and examples!
  4. 4. When to use it?● Good choice to build an application server – Allows to implement custom protocols – Dont need to worry (too much) about concurrency – Layered architecture allows to reuse code● And not so good for building a web application – Little support for web technologies – There are much better tools out there
  5. 5. The basic API● Channel: think of it as a connection● MessageEvent: represents the transmission or reception of a message● ChannelHandler: reacts to events that happen in a Channel & contains the app logic● ChannelPipeline: is an ordered list of ChannelHandlers
  6. 6. Socket.read() Socket.write() Upstream Handler Upstream / Downstream HandlerDownstream Handler The basic API Upstream Handler ChannelPipeline
  7. 7. Example: echo serverpublic class EchoServer { public static void main(String[] args) { // ChannelFactory manages the creation/removal of Channels ChannelFactory factory = new NioServerSocketChannelFactory( Executors.newCachedThreadPool(), Executors.newCachedThreadPool()); // Using helper class to boostrap... ServerBootstrap bootstrap = new ServerBootstrap(factory); // Define our ChannelPipelines bootstrap.setPipelineFactory(new ChannelPipelineFactory() { public ChannelPipeline getPipeline() { ChannelPipeline pipeline = getPipeline(); pipeline.addLast("echoHandler", new EchoHandler()); return pipeline; } }); bootstrap.bind(new InetSocketAddress(8080)); // Thats all! }
  8. 8. Example: echo serverpublic class EchoHandler extends SimpleChannelUpstreamHandler { @Override public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) throws Exception { // ctx allows to access to the Channel and ChannelPipeline Channel ch = ctx.getChannel(); // In Netty3.6 Messages are of class Object // This is improved in Netty 4 where ChannelHandlers are // typed with the message they handle ch.write(e.getMessage()); } @Override public void exceptionCaught(ChannelHandlerContext ctx, ExceptionEvent e) { // Something unexpected: closed connection, timeout? e.getCause().printStackTrace(); Channel ch = e.getChannel(); ch.close(); }
  9. 9. Thread model● One boss thread for each socket. Accepts connections and passes them to the workers● A worker thread performs non-blocking logic for one or multiple Channels● If some blocking operations are needed (e.g. access to DB or files), those ChannelHandlers must be moved to another executor
  10. 10. Example: webservicepublic class WebServicePipelineFactory implementsChannelPipelineFactory { private static final ExecutionHandler executionHandler = new ExecutionHandler( new OrderedMemoryAwareThreadPoolExecutor( 16, 1048576, 1048576)); @Override public ChannelPipeline getPipeline() throws Exception { ChannelPipeline p = pipeline(); p.addLast("decoder", new HttpRequestDecoder()); p.addLast("aggregator", new HttpChunkAggregator(65536)); p.addLast("encoder", new HttpResponseEncoder()); p.addLast("deflater", new HttpContentCompressor()); // The executor is shared among pipelines. All handlers // added after will be executed in another thread pool p.addLast("executor", executionHandler); p.addLast("myHandler", new MyBlockingHandler()); return p; }

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