netty 4 echo server in clojure https://github.com/netty/netty/blob/master/example/src/main/java/io/netty/example/echo/EchoServer.java

4.0.12.Final.clj

;;; based on the discussion at https://groups.google.com/d/msg/netty/mcGswAZ5NeQ/ivG9snRSFy4J

(ns netty4.core
  (:import   [io.netty.bootstrap AbstractBootstrap ServerBootstrap]
             [io.netty.channel ChannelFuture ChannelInitializer ChannelOption
                               ChannelHandlerContext ChannelInboundHandlerAdapter ChannelHandler]
             [io.netty.handler.logging LogLevel LoggingHandler]
             io.netty.buffer.ByteBuf
             io.netty.channel.socket.SocketChannel
             io.netty.channel.nio.NioEventLoopGroup
             io.netty.channel.socket.nio.NioServerSocketChannel
             java.util.concurrent.atomic.AtomicInteger)
  (:use [clojure.stacktrace])
  (:gen-class))

(def echo-server-handler
  (proxy [ChannelInboundHandlerAdapter] []
    (channelRead [ctx msg]       (.write ctx msg))
    (channelReadComplete [ctx]  (.flush ctx))
    (exceptionCaught [ctx cause]
      (print-stack-trace cause)
      (.close ctx))))

(defn -main []
  (let [b (ServerBootstrap.)
        elg1 (NioEventLoopGroup.)
        elg2 (NioEventLoopGroup.)
        shutdown #(do (.shutdownGracefully elg1)
                      (.shutdownGracefully elg2))]
    (->  b
         (.group elg1 elg2)
         (.channel io.netty.channel.socket.nio.NioServerSocketChannel)
         (.option  ChannelOption/SO_BACKLOG (int 100))
         (.childHandler
          (proxy [ChannelInitializer] []
            (initChannel [ch]
              (-> ch  (.pipeline)
                  (.addLast
                   (into-array ChannelHandler [echo-server-handler]))))))
         (.bind 2424))
    (println b) ; print the server bootstrap object
    shutdown))

(def r (-main))
(r) ;; call to terminate server

gistfile1.clj

(ns index-server.netty
  (:import   [io.netty.bootstrap AbstractBootstrap ServerBootstrap]
             [io.netty.channel ChannelFuture ChannelInitializer ChannelOption 
                               ChannelHandlerContext ChannelInboundByteHandlerAdapter]
             [io.netty.handler.logging LogLevel LoggingHandler]
             io.netty.buffer.ByteBuf
             io.netty.channel.socket.SocketChannel
             io.netty.channel.nio.NioEventLoopGroup
             io.netty.channel.socket.nio.NioServerSocketChannel
             java.util.concurrent.atomic.AtomicInteger)
  (:use [clojure.stacktrace])
  (:gen-class))

(defn echo-server-handler []
  (proxy [ChannelInboundByteHandlerAdapter] []
    (inboundBufferUpdated [this  ctx in]
      (let [out (.nextOutboundByteBuffer ctx)]
        (.writeBytes out in)
        (.flust ctx)))
    (exceptionCaught [this ctx cause]
      (print-stack-trace cause)
      (.close ctx))))


(defn -main []
  (let [b (ServerBootstrap.)]
    (try
      (->  b
          (.group (NioEventLoopGroup.) (NioEventLoopGroup.))
          (.channel io.netty.channel.socket.nio.NioServerSocketChannel)
          (.option  ChannelOption/SO_BACKLOG 100)
          (.childHandler
           (proxy [ChannelInitializer] []
             (initChannel [this ch]
               (-> ch
                   (.pipeline)
                   (.addLast (LoggingHandler. LogLevel/INFO)
                             (echo-server-handler)))))))

      (println b) ; print the server bootstrap object
      (let [f (-> b
                  (.bind 2424)
                  (.sync))]
        (-> f
            (.channel)
            (.closeFuture)
            (.sync)))
      (finally (.shutdown b)))))

gistfile2.clj

(ns test-app.core
  (:import   [io.netty.bootstrap AbstractBootstrap ServerBootstrap]
             [io.netty.channel ChannelFuture ChannelInitializer ChannelOption
              ChannelHandlerContext ChannelInboundByteHandlerAdapter]
             [io.netty.handler.logging LogLevel LoggingHandler]
             io.netty.buffer.ByteBuf
             io.netty.channel.socket.SocketChannel
             io.netty.channel.nio.NioEventLoopGroup
             io.netty.channel.socket.nio.NioServerSocketChannel
             java.util.concurrent.atomic.AtomicInteger)
  (:use [clojure.stacktrace])
  (:gen-class))


(def b (ServerBootstrap.))
(.group b (NioEventLoopGroup.))
(.channel b NioServerSocketChannel)
;(.option b ChannelOption/SO_BACKLOG 100)

(.childHandler b
  (proxy [ChannelInitializer] []
    (initChannel [ch] (println "new connection"))))

(.bind b 9999)

gistfile2.clj - this is a first working version