Java互操作性--Netty + Clojure

Question

我正在尝试通过Clojure使用Netty。我能够启动服务器，但是它无法初始化接受的套接字。以下是错误消息和代码。有人知道问题出在哪里吗？我认为问题出在 (Channels/pipeline (server-handler)) 上。谢谢。

错误消息

#<NioServerSocketChannel [id: 0x01c888d9, /0.0.0.0:843]>
Jun 6, 2012 12:15:35 PM org.jboss.netty.channel.socket.nio.NioServerSocketPipelineSink
WARNING: Failed to initialize an accepted socket.
java.lang.IllegalArgumentException: No matching method found: pipeline

project.clj

(defproject protocol "1.0.0-SNAPSHOT"
  :description "Upload Protocol Server"
  :dependencies [
    [org.clojure/clojure "1.2.1"]
    [io.netty/netty "3.4.5.Final"]])

core.clj

(ns protocol.core
    (:import (java.net InetSocketAddress)
             (java.util.concurrent Executors)
             (org.jboss.netty.bootstrap ServerBootstrap)
             (org.jboss.netty.channel Channels ChannelPipelineFactory SimpleChannelHandler)
             (org.jboss.netty.channel.socket.nio NioServerSocketChannelFactory)
             (org.jboss.netty.buffer ChannelBuffers)))

(def policy
    "<content>Test</content>")


(defn server-handler
    "Returns netty handler."
    []
    (proxy [SimpleChannelHandler] []
        (messageReceived [ctx e]
            (let [ch (.getChannel e)]
                (.write ch policy)
                (.close ch)))

        (channelConnected [ctx e]
            (let [ch (.getChannel e)]
                (.write ch policy)
                (.close ch)))

        (exceptionCaught [ctx e]
            (let [ex (.getCause e)]
                (println "Exception" ex)
                (-> e .getChannel .close)))))

(defn setup-pipeline
    "Returns channel pipeline."
    []
    (proxy [ChannelPipelineFactory] []
        (getPipeline []
            (Channels/pipeline (server-handler)))))

(defn startup
    "Starts netty server."
    [port]
    (let [channel-factory (NioServerSocketChannelFactory. (Executors/newCachedThreadPool) (Executors/newCachedThreadPool))
          bootstrap (ServerBootstrap. channel-factory)]
        (.setPipelineFactory bootstrap (setup-pipeline))
        (.setOption bootstrap "child.tcpNoDelay" true)
        (.setOption bootstrap "child.keepAlive" true)
        (.bind bootstrap (InetSocketAddress. port))))

- Ari

Answer 1

您的代码存在三个问题：

1. 与 vararg Channels.channel() 方法的 Java 互操作。 您可以创建一个通道处理程序向量，并使用 (into-array ChannelHandler ..) 进行封装。

2. 无法直接将 String 对象写入 Netty 通道。 您必须首先将字符串写入 ChannelBuffer，然后再写入该缓冲区或使用 StringCodecHandler。

3. 向 Netty 通道写入是异步的，因此不能立即关闭它。 您必须注册一个 future 监听器，并在完成时关闭通道。

以下是可行的代码。

  (ns clj-netty.core
   (:import (java.net InetSocketAddress)
            (java.util.concurrent Executors)
            (org.jboss.netty.bootstrap ServerBootstrap)
            (org.jboss.netty.buffer ChannelBuffers)
            (org.jboss.netty.channel Channels ChannelFutureListener ChannelHandler ChannelPipelineFactory SimpleChannelHandler)
           (org.jboss.netty.channel.socket.nio NioServerSocketChannelFactory)
           (org.jboss.netty.buffer ChannelBuffers)))


(def policy
  (ChannelBuffers/copiedBuffer
    (.getBytes "<content>Test</content>")))


(defn server-handler
  "Returns netty handler."
  []
  (proxy [SimpleChannelHandler] []
    (messageReceived [ctx e]
      (let [ch (.getChannel e)]
        (.addListener
          (.write ch policy)
          (ChannelFutureListener/CLOSE))))

    (channelConnected [ctx e]
      (let [ch (.getChannel e)]
        (.addListener
          (.write ch policy)
          (ChannelFutureListener/CLOSE))))

    (exceptionCaught [ctx e]
      (let [ex (.getCause e)]
        (println "Exception" ex)
        (-> e .getChannel .close)))))

(defn setup-pipeline
  "Returns channel pipeline."
  []
  (proxy [ChannelPipelineFactory] []
    (getPipeline []
      (let [handler (server-handler)]
        (Channels/pipeline (into-array ChannelHandler [handler]))))))



 (defn startup
      "Starts netty server."
      [port]
      (let [channel-factory (NioServerSocketChannelFactory. (Executors/newCachedThreadPool) (Executors/newCachedThreadPool))
            bootstrap (ServerBootstrap. channel-factory)]
        (.setPipelineFactory bootstrap (setup-pipeline))
        (.setOption bootstrap "child.tcpNoDelay" true)
        (.setOption bootstrap "child.keepAlive" true)
        (.bind bootstrap (InetSocketAddress. port))))

请看Aleph（也使用Netty），它可以用来构建许多不同协议的客户端和服务器，并且有易于理解的Clojure API。

- Jestan Nirojan

---

感谢您清晰详细的解释，非常有帮助。我当然打算尝试Aleph，但我想一举两得——在练习Clojure的同时学习Netty。 - Ari

Answer 2

在2021年，构建Clojure服务的最简单方法是采用Donkey，在Netty之上提供了良好的Clojure互操作性，而Vert.x则使用Netty作为后端。 Donkey相对较新，尚没有很多文档，因此请查看这个博客，其中涵盖了一个相关的开源项目（源代码可用），包括架构，设计，编码和负载测试。

- Glenn