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Java NIO
Java NIO (New IO)是Java 1.4版本开始引入的新的IO API。和IO的区别在于NIO是一个异步、非阻塞的IO，可以用一个线程管理多个连接。比如1个服务器，5个客户端，如果用IO，在服务器上就需要5个线程，而使用NIO的话，只需要1个线程就可以同时管理5个连接，节约了资源。
NIO的核心部分包括：Channel、Buffer和Selector。Channel把数据读写到Buffer，或者说通过Buffer实现数据的读写。Selector可以同时管理多个Channel，Channel注册到Selector，当Channel中有事件就绪时，Selector执行获得一个SelectionKey集合，并进行处理，从而实现了异步、非阻塞，一个线程管理多个连接。
下面的例子，通过NIO实现了1个服务器线程管理5个客户端线程，直接上代码。
NIOServer.java：
package server;import java.io.IOException;import java.net.InetSocketAddress;import java.net.ServerSocket;import java.nio.ByteBuffer;import java.nio.channels.SelectionKey;import java.nio.channels.Selector;import java.nio.channels.ServerSocketChannel;import java.nio.channels.SocketChannel;import java.util.Iterator;import java.util.Set;public class NIOServer { // 端口号 final static int startPort = 10000; int[] port = {startPort, startPort+1, startPort+2, startPort+3, startPort+4}; // Channel编号 int[] num = {0, 1, 2, 3, 4}; // Channel发送消息的次数 int[] times = {0, 0, 0, 0, 0}; // 缓冲区大小 private int BLOCK = 4096; // 接收数据缓冲区 private ByteBuffer sendbuffer = ByteBuffer.allocate(BLOCK); // 发送数据缓冲区 private ByteBuffer receivebuffer = ByteBuffer.allocate(BLOCK); private Selector selector; // 构造函数 public NIOServer(String host) throws IOException{ // 打开ServerSocketChannel ServerSocketChannel serverSocketChannel1 = ServerSocketChannel.open(); ServerSocketChannel serverSocketChannel2 = ServerSocketChannel.open(); ServerSocketChannel serverSocketChannel3 = ServerSocketChannel.open(); ServerSocketChannel serverSocketChannel4 = ServerSocketChannel.open(); ServerSocketChannel serverSocketChannel5 = ServerSocketChannel.open(); // 设置为非阻塞 serverSocketChannel1.configureBlocking(false); serverSocketChannel2.configureBlocking(false); serverSocketChannel3.configureBlocking(false); serverSocketChannel4.configureBlocking(false); serverSocketChannel5.configureBlocking(false); // 获得ServerSocket ServerSocket serverSocket1 = serverSocketChannel1.socket(); ServerSocket serverSocket2 = serverSocketChannel2.socket(); ServerSocket serverSocket3 = serverSocketChannel3.socket(); ServerSocket serverSocket4 = serverSocketChannel4.socket(); ServerSocket serverSocket5 = serverSocketChannel5.socket(); // 绑定主机和端口 serverSocket1.bind(new InetSocketAddress(host, port[0])); serverSocket2.bind(new InetSocketAddress(host, port[1])); serverSocket3.bind(new InetSocketAddress(host, port[2])); serverSocket4.bind(new InetSocketAddress(host, port[3])); serverSocket5.bind(new InetSocketAddress(host, port[4])); // 获得Selector selector = Selector.open(); // 注册到selector,等待连接 serverSocketChannel1.register(selector, SelectionKey.OP_ACCEPT, num[0]); serverSocketChannel2.register(selector, SelectionKey.OP_ACCEPT, num[1]); serverSocketChannel3.register(selector, SelectionKey.OP_ACCEPT, num[2]); serverSocketChannel4.register(selector, SelectionKey.OP_ACCEPT, num[3]); serverSocketChannel5.register(selector, SelectionKey.OP_ACCEPT, num[4]); // 成功 System.out.println("Server start (Host:" + host + ", Port:" + port[0] + ") successful!"); System.out.println("Server start (Host:" + host + ", Port:" + port[1] + ") successful!"); System.out.println("Server start (Host:" + host + ", Port:" + port[2] + ") successful!"); System.out.println("Server start (Host:" + host + ", Port:" + port[3] + ") successful!"); System.out.println("Server start (Host:" + host + ", Port:" + port[4] + ") successful!"); } // 监听 public void listen() throws IOException{ while (true) { // 选择一组键,并且相应的Channel已经打开 selector.select(); // 返回此选择器的SelectionKey集 Set<SelectionKey> selectionKeys = selector.selectedKeys(); Iterator<SelectionKey> iterator = selectionKeys.iterator(); while (iterator.hasNext()) { SelectionKey selectionKey = iterator.next(); // 先删除该SelectionKey,再处理 iterator.remove(); handleKey(selectionKey); } } } // 处理请求 private void handleKey(SelectionKey selectionKey) throws IOException { // 接受请求 ServerSocketChannel server = null; SocketChannel client = null; String receiveText; String sendText; int count = 0; int num = 0; num = (int) selectionKey.attachment(); // 此SelectionKey是否可以Accept if (selectionKey.isAcceptable()) { // 获得此SelectionKey的Channel server = (ServerSocketChannel) selectionKey.channel(); // 接受连接,返回Channel client = server.accept(); // 配置为非阻塞 client.configureBlocking(false); // 注册到selector，等待读取 client.register(selector, SelectionKey.OP_READ, num); } // 此SelectionKey是否可以Read else if (selectionKey.isReadable()) { // 获得此SelectionKey的Channel client = (SocketChannel) selectionKey.channel(); // 清空缓冲区 receivebuffer.clear(); // 读取客户端发送来的数据到缓冲区中 count = client.read(receivebuffer); if (count > 0) { // Byte转换成String receiveText = new String(receivebuffer.array(), 0, count); System.out.println("Server Channel " + num + " received from client:" + receiveText); // 注册到selector，等待写入 client.register(selector, SelectionKey.OP_WRITE, num); } } // 此SelectionKey是否可以Write else if (selectionKey.isWritable()) { // 清空缓冲区 sendbuffer.clear(); // 获得此SelectionKey的Channel client = (SocketChannel) selectionKey.channel(); int tim = ++times[num]; sendText = "Server(Number:" + num + " Times:" + tim +")"; // 向缓冲区中输入数据 sendbuffer.put(sendText.getBytes()); // 读写模式切换 sendbuffer.flip(); // 输出到Channel client.write(sendbuffer); client.register(selector, SelectionKey.OP_READ, num); } } public static void main(String[] args) throws IOException { // 启动服务器 NIOServer nioserver = new NIOServer("localhost"); nioserver.listen(); }}
NIOClient.java：
package client;import java.io.IOException;import java.net.InetSocketAddress;import java.nio.ByteBuffer;import java.nio.channels.SelectionKey;import java.nio.channels.Selector;import java.nio.channels.SocketChannel;import java.util.Iterator;import java.util.Set;public class NIOClient extends Thread{ // Client编号 int num; // 端口号 int port; // 缓冲区大小 private int BLOCK = 4096; // 接收数据缓冲区 private ByteBuffer sendbuffer = ByteBuffer.allocate(BLOCK); // 发送数据缓冲区 private ByteBuffer receivebuffer = ByteBuffer.allocate(BLOCK); private Selector selector; Set<SelectionKey> selectionKeys; Iterator<SelectionKey> iterator; SelectionKey selectionKey; SocketChannel client; String receiveText; String sendText; int count = 0; // 发送消息的次数 int flag = 0; public NIOClient(int num) throws IOException{ this.num = num; this.port = 10000 + num; InetSocketAddress SERVER_ADDRESS = new InetSocketAddress("localhost", port); // 打开SocketChannel SocketChannel socketChannel = SocketChannel.open(); // 设置为非阻塞 socketChannel.configureBlocking(false); // 获得Selector selector = Selector.open(); // 注册连接服务端socket动作 socketChannel.register(selector, SelectionKey.OP_CONNECT); // 连接 socketChannel.connect(SERVER_ADDRESS); } public void run(){ while (true){ try { // 选择 selector.select(); selectionKeys = selector.selectedKeys(); iterator = selectionKeys.iterator(); while (iterator.hasNext()) { selectionKey = iterator.next(); if (selectionKey.isConnectable()) { client = (SocketChannel) selectionKey.channel(); // 判断此Channel上是否正在进行连接操作 if (client.isConnectionPending()) { // 完成连接 client.finishConnect(); System.out.println("Client " + num + " connected!"); sendbuffer.clear(); flag++; String sendString = "Client " + num + " send: " + flag + "!"; sendbuffer.put(sendString.getBytes()); sendbuffer.flip(); client.write(sendbuffer); } client.register(selector, SelectionKey.OP_READ); } else if (selectionKey.isReadable()) { client = (SocketChannel) selectionKey.channel(); //将缓冲区清空以备下次读取 receivebuffer.clear(); //读取服务器发送来的数据到缓冲区中 count=client.read(receivebuffer); if(count>0){ receiveText = new String( receivebuffer.array(),0,count); System.out.println("Client " + num + " received from server: " + receiveText); client.register(selector, SelectionKey.OP_WRITE); } } else if (selectionKey.isWritable()) { sendbuffer.clear(); client = (SocketChannel) selectionKey.channel(); flag++; String sendString = "Client " + num + " send: " + flag + "!"; sendbuffer.put(sendString.getBytes()); // 将缓冲区各标志复位,因为向里面put了数据标志被改变要想从中读取数据发向服务器,就要复位 sendbuffer.flip(); client.write(sendbuffer); client.register(selector, SelectionKey.OP_READ); } } selectionKeys.clear(); } catch (IOException e) { // 出错 e.printStackTrace(); } try { Thread.sleep(1000); } catch (InterruptedException e) { // 出错 e.printStackTrace(); } } } public static void main(String[] args) throws IOException { // 启动客户端 NIOClient nioclient0 = new NIOClient(0); NIOClient nioclient1 = new NIOClient(1); NIOClient nioclient2 = new NIOClient(2); NIOClient nioclient3 = new NIOClient(3); NIOClient nioclient4 = new NIOClient(4); nioclient0.start(); nioclient1.start(); nioclient2.start(); nioclient3.start(); nioclient4.start(); }}
Java NIO
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