Java网络编程-IO多路复用(单线程)

1. 简介

IO多路复用(multiplexing)属于同步IO网络模型

是以Reactor模式实现

常见的IO多路复用应用有：select、poll、epoll

有关于select的应用方式，请参阅[C语言] 基于Linux的一对一Socket简易聊天程序实例

本篇文章采用Java的NIO框架来实现单线程的IO多路复用

2. Reactor模式的组成角色

1. Reactor：负责派发IO事件给对应的角色处理。为了监听IO事件，select必须实现在Reactor中。

2. Acceptor：负责接受client的连线，然后给client绑定一个Handler并注册IO事件到Reactor上监听。

3. Handler：负责处理与client交互的事件或行为。通常因为Handler要处理与所对应client交互的多个事件或行为，为了简化设计，会以状态模式来实现Handler。

3. 代码实现

[TCPReactor.java]

 // Reactor線程
 package server;

 import java.io.IOException;
 import java.net.InetSocketAddress;
 import java.nio.channels.SelectionKey;
 import java.nio.channels.Selector;
 import java.nio.channels.ServerSocketChannel;
 import java.util.Iterator;
 import java.util.Set;

 public class TCPReactor implements Runnable {

     private final ServerSocketChannel ssc;
     private final Selector selector;

     public TCPReactor(int port) throws IOException {
         selector = Selector.open();
         ssc = ServerSocketChannel.open();
         InetSocketAddress addr = new InetSocketAddress(port);
         ssc.socket().bind(addr); // 在ServerSocketChannel綁定監聽端口
         ssc.configureBlocking(false); // 設置ServerSocketChannel為非阻塞
         SelectionKey sk = ssc.register(selector, SelectionKey.OP_ACCEPT); // ServerSocketChannel向selector註冊一個OP_ACCEPT事件，然後返回該通道的key
         sk.attach(new Acceptor(selector, ssc)); // 給定key一個附加的Acceptor對象
     }

     @Override
     public void run() {
         while (!Thread.interrupted()) { // 在線程被中斷前持續運行
             System.out.println("Waiting for new event on port: " + ssc.socket().getLocalPort() + "...");
             try {
                 if (selector.select() == 0) // 若沒有事件就緒則不往下執行
                     continue;
             } catch (IOException e) {
                 // TODO Auto-generated catch block
                 e.printStackTrace();
             }
             Set selectedKeys = selector.selectedKeys(); // 取得所有已就緒事件的key集合
             Iterator it = selectedKeys.iterator();
             while (it.hasNext()) {
                 dispatch((SelectionKey) (it.next())); // 根據事件的key進行調度
                 it.remove();
             }
         }
     }

     /*
      * name: dispatch(SelectionKey key)
      * description: 調度方法，根據事件綁定的對象開新線程
      */
     private void dispatch(SelectionKey key) {
         Runnable r = (Runnable) (key.attachment()); // 根據事件之key綁定的對象開新線程
         if (r != null)
             r.run();
     }

 }

[Acceptor.java]

 // 接受連線請求線程
 package server;

 import java.io.IOException;
 import java.nio.channels.SelectionKey;
 import java.nio.channels.Selector;
 import java.nio.channels.ServerSocketChannel;
 import java.nio.channels.SocketChannel;

 public class Acceptor implements Runnable {

     private final ServerSocketChannel ssc;
     private final Selector selector;

     public Acceptor(Selector selector, ServerSocketChannel ssc) {
         this.ssc=ssc;
         this.selector=selector;
     }

     @Override
     public void run() {
         try {
             SocketChannel sc= ssc.accept(); // 接受client連線請求
             System.out.println(sc.socket().getRemoteSocketAddress().toString() + " is connected.");

             if(sc!=null) {
                 sc.configureBlocking(false); // 設置為非阻塞
                 SelectionKey sk = sc.register(selector, SelectionKey.OP_READ); // SocketChannel向selector註冊一個OP_READ事件，然後返回該通道的key
                 selector.wakeup(); // 使一個阻塞住的selector操作立即返回
                 sk.attach(new TCPHandler(sk, sc)); // 給定key一個附加的TCPHandler對象
             }

         } catch (IOException e) {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }
     }


 }

我们先来简单点的，Handler不以​​状态模式实现，只以比较直觉的方式实现。

[TCPHandler.java]

 // Handler線程
 package server;

 import java.io.IOException;
 import java.nio.ByteBuffer;
 import java.nio.channels.SelectionKey;
 import java.nio.channels.SocketChannel;
 import java.util.concurrent.LinkedBlockingQueue;
 import java.util.concurrent.ThreadPoolExecutor;
 import java.util.concurrent.TimeUnit;

 public class TCPHandler implements Runnable {

     private final SelectionKey sk;
     private final SocketChannel sc;

     int state;

     public TCPHandler(SelectionKey sk, SocketChannel sc) {
         this.sk = sk;
         this.sc = sc;
         state = 0; // 初始狀態設定為READING
     }

     @Override
     public void run() {
         try {
             if (state == 0)
                 read(); // 讀取網絡數據
             else
                 send(); // 發送網絡數據

         } catch (IOException e) {
             System.out.println("[Warning!] A client has been closed.");
             closeChannel();
         }
     }

     private void closeChannel() {
         try {
             sk.cancel();
             sc.close();
         } catch (IOException e1) {
             e1.printStackTrace();
         }
     }

     private synchronized void read() throws IOException {
         // non-blocking下不可用Readers，因為Readers不支援non-blocking
         byte[] arr = new byte[1024];
         ByteBuffer buf = ByteBuffer.wrap(arr);

         int numBytes = sc.read(buf); // 讀取字符串
         if(numBytes == -1)
         {
             System.out.println("[Warning!] A client has been closed.");
             closeChannel();
             return;
         }
         String str = new String(arr); // 將讀取到的byte內容轉為字符串型態
         if ((str != null) && !str.equals(" ")) {
             process(str); // 邏輯處理
             System.out.println(sc.socket().getRemoteSocketAddress().toString()
                     + " > " + str);
             state = 1; // 改變狀態
             sk.interestOps(SelectionKey.OP_WRITE); // 通過key改變通道註冊的事件
             sk.selector().wakeup(); // 使一個阻塞住的selector操作立即返回
         }
     }

     private void send() throws IOException  {
         // get message from message queue

         String str = "Your message has sent to "
                 + sc.socket().getLocalSocketAddress().toString() + "\r\n";
         ByteBuffer buf = ByteBuffer.wrap(str.getBytes()); // wrap自動把buf的position設為0，所以不需要再flip()

         while (buf.hasRemaining()) {
             sc.write(buf); // 回傳給client回應字符串，發送buf的position位置 到limit位置為止之間的內容
         }

         state = 0; // 改變狀態
         sk.interestOps(SelectionKey.OP_READ); // 通過key改變通道註冊的事件
         sk.selector().wakeup(); // 使一個阻塞住的selector操作立即返回
     }

     void process(String str) {
         // do process(decode, logically process, encode)..
         // ..
     }
 }

最后是主程序代码

[Main.java]

 package server;

 import java.io.IOException;

 public class Main {


     public static void main(String[] args) {
         // TODO Auto-generated method stub
         try {
             TCPReactor reactor = new TCPReactor(1333);
             reactor.run();
         } catch (IOException e) {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }
     }

 }

下面附上客戶端代碼：

[Client.java]

 package main.pkg;

 import java.io.BufferedReader;
 import java.io.IOException;
 import java.io.InputStreamReader;
 import java.io.PrintWriter;
 import java.net.Socket;
 import java.net.UnknownHostException;

 public class Client {

     /**
      * @param args
      */
     public static void main(String[] args) {
         // TODO Auto-generated method stub
         String hostname=args[0];
         int port = Integer.parseInt(args[1]);
         //String hostname="127.0.0.1";
         //int port=1333;

         System.out.println("Connecting to "+ hostname +":"+port);
         try {
             Socket client = new Socket(hostname, port); // 連接至目的地
             System.out.println("Connected to "+ hostname);

             PrintWriter out = new PrintWriter(client.getOutputStream());
             BufferedReader in = new BufferedReader(new InputStreamReader(client.getInputStream()));
             BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in));
             String input;

             while((input=stdIn.readLine()) != null) { // 讀取輸入
                 out.println(input); // 發送輸入的字符串
                 out.flush(); // 強制將緩衝區內的數據輸出
                 if(input.equals("exit"))
                 {
                     break;
                 }
                 System.out.println("server: "+in.readLine());
             }
             client.close();
             System.out.println("client stop.");
         } catch (UnknownHostException e) {
             // TODO Auto-generated catch block
             System.err.println("Don't know about host: " + hostname);
         } catch (IOException e) {
             // TODO Auto-generated catch block
             System.err.println("Couldn't get I/O for the socket connection");
         }

     }

 }