Netty Best Practices a.k.a Faster == Better

public class HttpHandler extends SimpleChannelInboundHandler<HttpRequest> {
  @Override
  public void channelRead(ChannelHandlerContext ctx, HttpRequest req) {
    ChannelFuture future = ctx.writeAndFlush(createResponse(req)); (1)
    if (!isKeepAlive(req)) {
      future.addListener(ChannelFutureListener.CLOSE); (2)
    }
  }
}

public class HttpPipeliningHandler extends SimpleChannelInboundHandler<HttpRequest> {
  @Override
  public void channelRead(ChannelHandlerContext ctx, HttpRequest req) {
    ChannelFuture future = ctx.writeAnd(createResponse(req)); (1)
    if (!isKeepAlive(req)) {
      future.addListener(ChannelFutureListener.CLOSE); (2)
    }
  }
  @Override
  public void channelReadComplete(ChannelHandlerContext ctx) {
    ctx.flush(); (3)
  }
}

public class BlindlyWriteHandler extends ChannelInboundHandlerAdapter {
  @Override
  public void channelActive(ChannelHandlerContext ctx) throws Exception {
    while(needsToWrite) { (1)
        ctx.writeAndFlush(createMessage());
    }
  }
}

public class GracefulWriteHandler extends ChannelInboundHandlerAdapter {
  @Override
  public void channelActive(ChannelHandlerContext ctx) {
    writeIfPossible(ctx.channel());
  }
  @Override
  public void channelWritabilityChanged(ChannelHandlerContext ctx) {
    writeIfPossible(ctx.channel());
  }

  private void writeIfPossible(Channel channel) {
    while(needsToWrite && channel.isWritable()) { (1)
      channel.writeAndFlush(createMessage());
    }
  }
}

ServerBootstrap bootstrap = new ServerBootstrap();
bootstrap.childOption(ChannelOption.WRITE_BUFFER_HIGH_WATER_MARK, 32 * 1024);
bootstrap.childOption(ChannelOption.WRITE_BUFFER_LOW_WATER_MARK, 8 * 1024);

Bootstrap bootstrap = new Bootstrap();
bootstrap.option(ChannelOption.WRITE_BUFFER_HIGH_WATER_MARK, 32 * 1024);
bootstrap.option(ChannelOption.WRITE_BUFFER_LOW_WATER_MARK, 8 * 1024);

public enum CustomEvents {
  MyCustomEvent
}

public class CustomEventHandler extends ChannelInboundHandlerAdapter {
  @Override
  public void userEventTriggered(ChannelHandlerContext ctx, Object evt) {
    if (evt == MyCustomEvent) { // do something}
  }
}

ChannelPipeline pipeline = channel.pipeline();
pipeline.fireUserEventTriggered(MyCustomEvent);

Bootstrap bootstrap = new Bootstrap();
bootstrap.option(ChannelOption.ALLOCATOR, PooledByteBufAllocator.DEFAULT);
ServerBootstrap bootstrap = new ServerBootstrap();
bootstrap.childOption(ChannelOption.ALLOCATOR, PooledByteBufAllocator.DEFAULT);

java -Dio.netty.allocator.numDirectArenas=... -Dio.netty.allocator.numHeapArenas=...

ByteBuf buf = ...;
int index = -1;
for (int i = buf.readerIndex(); index == -1 && i <  buf.writerIndex(); i++) {
  if (buf.getByte(i) == '\n') {
    index = i;
  }
}

ByteBuf buf = ...;
int index = buf.forEachByte(new ByteBufProcessor() {
  @Override
  public boolean process(byte value) {
    return value != '\n';
  }
});

Channel channel = ...;
FileChannel fc = ...;
channel.writeAndFlush(new DefaultFileRegion(fc, 0, fileLength));

Bootstrap bootstrap = new Bootstrap().group(new NioEventLoopGroup());
Bootstrap bootstrap2 = new Bootstrap().group(new NioEventLoopGroup());

EventLoopGroup group = new NioEventLoopGroup();
Bootstrap bootstrap = new Bootstrap().group(group);
Bootstrap bootstrap2 = new Bootstrap().group(group);

public class ProxyHandler extends ChannelInboundHandlerAdapter {
  @Override
  public void channelActive(ChannelHandlerContext ctx) { (1)
    final Channel inboundChannel = ctx.channel();
    Bootstrap b = new Bootstrap();
    b.group(new NioEventLooopGroup()); (2)
    ...
    ChannelFuture f = b.connect(remoteHost, remotePort);
    ...
  }
}

public class ProxyHandler extends ChannelInboundHandlerAdapter {
  @Override
  public void channelActive(ChannelHandlerContext ctx) { (1)
    final Channel inboundChannel = ctx.channel();
    Bootstrap b = new Bootstrap();
    b.group(inboundChannel.eventLoop()); (2)
    ...
    ChannelFuture f = b.connect(remoteHost, remotePort);
    ...
  }
}

channel.write(msg1);
channel.writeAndFlush(msg3);

channel.eventLoop().execute(new Runnable() {
  @Override
  public void run() {
    channel.write(msg1);
    channel.writeAndFlush(msg3);
  }
});

public class YourHandler extends ChannelInboundHandlerAdapter {
  @Override
  public void channelActive(ChannelHandlerContext ctx) {
    // BAD (most of the times)
    ctx.channel().writeAndFlush(msg); (1)

    // GOOD
    ctx.writeAndFlush(msg); (2)
   }
}

@ChannelHandler.Shareable (1)
public class StatelessHandler extends ChannelInboundHandlerAdapter {
  @Override
  public void channelActive(ChannelHandlerContext ctx) {
    logger.debug("Now client from " + ctx.channel().remoteAddress().toString());
   }
}

public class MyInitializer extends ChannelInitializer<Channel> {
  private static final ChannelHandler INSTANCE = new StatelessHandler();
  @Override
  public void initChannel(Channel ch) {
    ch.pipeline().addLast(INSTANCE);
  }
}

public class OneTimeHandler extends ChannelInboundHandlerAdapter {
  @Override
  public void channelActive(ChannelHandlerContext ctx) {
    doOneTimeAction();
    ctx.channel().pipeline().remove(this); (1)
   }
}

public class EncodeActsOnByteArray extends MessageToByteEncoder<YourMessage> {
  public EncodeActsOnByteArray() { super(false); } (1)
  @Override
  public encode(ChannelHandlerContext ctx, YourMessage msg, ByteBuf out) {
    byte[] array = out.array(); (2)
    int offset = out.arrayOffset() + out.writerIndex();
    out.writeIndex(out.writerIndex() + encode(msg, array, offset)); (3)
  }
  private int encode(YourMessage msg, byte[] array, int offset, int len) { ... }
}

channel.config().setAutoRead(false); (1)
channel.read(); (2)
channel.config().setAutoRead(true); (3)

import com.twitter.finagle.ssl.Ssl;
...

SSLEngine engine = Ssl.server("/path/to/cert.pem", "/path/to/key.pem", "/path/to/cachain.pem", null, null).self();
pipeline.addLast("ssl", new SslHandler(engine));

public class OuterClass {
  private final HeavyObject instance = ....;
  public void write() { channel.writeAndFlush(msg).addListener(
      new ChannelFutureListener() { ...}); }
}

public class OuterClass {
  private final HeavyObject instance = ....;
  public void write() { channel.writeAndFlush(msg).addListener(new ListenerImpl()); }

  private static final class ListenerImpl implements ChannelFutureListener { ... }
}

Bootstrap bootstrap = new Bootstrap().group(new NioEventLoopGroup());
bootstrap.channel(NioSocketChannel.class);

Bootstrap bootstrap = new Bootstrap().group(new EpollEventLoopGroup());
bootstrap.channel(EpollSocketChannel.class);