Java NIO 学习

关于Java NIO 基础，推荐 IBM developerWorks上的一篇文章，写的非常的好，作者是Greg Travis 。

NIO入门
https://www.ibm.com/developerworks/cn/education/java/j-nio/j-nio.html

NIO Socket Demo

这里贴一个我练习的一个NIO例子，该例子是在阅读学习《Netty权威指南 》这本书参考写的，为的是理解NIO的思想。

关键点我都写在注释中，特别要注意 I/O多路复用模型，把大量的I/O请求连接复用到一个Selector线程中去处理。

以下为例子：
场景：客户端向服务端发送一条请求当前时间的指令，服务端收到指令后返回当前时间给客户端输出。

客户端：TimeClient
服务端：TimeServer

TimeServer

/** * Created by kay on 2017/9/8. */public class TimeServer {    public static void main(String[] args) {        int port=8888;        MultiplexerTimeServer timeServer = new MultiplexerTimeServer(port);        new Thread(timeServer,"多路复用TimeServer启动").start();    }}

MultiplexerTimeServer 多路复用类，也就是服务端的处理线程

package com.kay.concurrent.nio.timesocket;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.ServerSocketChannel;import java.nio.channels.SocketChannel;import java.util.Date;import java.util.Iterator;import java.util.Set;/** * Created by kay on 2017/9/7. * 多路复用类 * 处理多个客户端的并发请求 * selector 多路复用器 */public class MultiplexerTimeServer implements Runnable{    private Selector selector;    private ServerSocketChannel servChannel;    private volatile boolean stop;    /**     * 初始化 绑定注册监听     * @param port     */    public MultiplexerTimeServer(int port) {        try {            selector=Selector.open();            servChannel = ServerSocketChannel.open();            servChannel.configureBlocking(false);    //设置非阻塞模式            servChannel.bind(new InetSocketAddress(port));  //绑定端口            servChannel.register(selector, SelectionKey.OP_ACCEPT); //监听准备连接            System.out.println("TimeServer 正在监听端口："+port);        } catch (IOException e) {            e.printStackTrace();            //初始化失败则退出，例如端口占用等            System.exit(1);        }    }    @Override    public void run() {        while (!stop) {            try {                //每隔一秒 轮询一次                selector.select(1000);                Set<SelectionKey> selectionKeys = selector.selectedKeys();                Iterator<SelectionKey> it = selectionKeys.iterator();                while (it.hasNext()) {                    SelectionKey key=it.next();                    it.remove();                    try {                        //处理准备好的事件                        handleInput(key);                    } catch (Exception e) {                        if(key!=null){                            key.cancel();                            if (key.channel() != null) {                                key.channel().close();                            }                        }                    }                }            } catch (Throwable t) {                t.printStackTrace();            }        }        //关闭多路复用器，绑定在上面的channel也会被自动关闭        if (selector != null) {            try {                selector.close();            } catch (IOException e) {                e.printStackTrace();            }        }    }    /**     * 统一事件处理，根据key 的类型作出相应处理     * 1.对方请求连接->accept->注册监听对方发的消息     * 2.对方发送消息->读取消息->做出响应     * @param key     * @throws IOException     */    private void handleInput(SelectionKey key) throws IOException{        //判断是否可用        if (key.isValid()) {            //判断是否是accept事件            if (key.isAcceptable()) {                //拿到这个key上面绑定的Channel，然后获取对面来的SocketChannel                //将这个channel注册 监听它的读事件（因为它已经连接了，所以就等着它发消息了）                ServerSocketChannel ssc= (ServerSocketChannel) key.channel();                SocketChannel sc=ssc.accept();                sc.configureBlocking(false);                System.out.println("--新请求接入,开始监听它发来的消息...");                sc.register(selector, SelectionKey.OP_READ);            }            //判断对方是否放消息来了，是就读取消息/作出响应            if (key.isReadable()) {                SocketChannel socketChannel = (SocketChannel) key.channel();                ByteBuffer readBuffer = ByteBuffer.allocate(1024);                int readBytes = socketChannel.read(readBuffer);                if (readBytes > 0) {                    readBuffer.flip();                    byte[] bytes = new byte[readBuffer.remaining()];                    readBuffer.get(bytes);                    String body = new String(bytes, "UTF-8");                    System.out.println("Time Server 接收到消息："+body);                    String currentTime="";                    if ("QUERY_TIME".equals(body)) {                        currentTime = "现在时间是：" + new Date(System.currentTimeMillis()).toString();                    } else {                        currentTime="指令错误！";                    }                    //作出响应                    doWrite(socketChannel,currentTime);                } else if (readBytes < 0) {                    key.cancel();                    socketChannel.close();                }else {                    ;//读到0字节忽略                }            }        }    }    //响应消息    private void doWrite(SocketChannel socketChannel, String response) throws IOException {        if (response != null && response.trim().length() > 0) {            byte[] bytes=response.getBytes();            ByteBuffer writeBuffer = ByteBuffer.allocate(bytes.length);            writeBuffer.put(bytes);            writeBuffer.flip();            socketChannel.write(writeBuffer);            System.out.println("--已发送响应");        }    }}

TimeClient 客户端

/** * Created by kay on 2017/9/8. */public class TimeCient {    public static void main(String[] args) {        int port=8888;        TimeClientHandle clientHandle=new TimeClientHandle("127.0.0.1",port);        new Thread(clientHandle,"TimeClient").start();    }}

TimeClientHandle 客户端处理线程

package com.kay.concurrent.nio.timesocket;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;/** * Created by kay on 2017/9/8. */public class TimeClientHandle implements Runnable {    private String host;    private int port;    private SocketChannel socketChannel;    private Selector selector;    private volatile boolean stop=false;    public TimeClientHandle(String host,int port) {        this.host=(host==null )? "127.0.0.1":host;        this.port=port;        try {            selector=Selector.open();            socketChannel = SocketChannel.open();            socketChannel.configureBlocking(false);        } catch (IOException e) {            e.printStackTrace();            System.exit(1);        }    }    @Override    public void run() {        try {            doConnect();        } catch (IOException e) {            e.printStackTrace();            System.exit(1);        }        while (!stop) {            try {                selector.select(1000);                Set<SelectionKey> selectionKeys = selector.selectedKeys();                Iterator<SelectionKey> it = selectionKeys.iterator();                SelectionKey key=null;                while (it.hasNext()) {                    key=it.next();                    it.remove();                    try {                        handleInput(key);                    } catch (Exception e) {                        if (key != null) {                            key.cancel();                            if (key.channel() != null) {                                key.channel().close();                            }                        }                    }                }            } catch (Exception e) {                e.printStackTrace();                System.exit(1);            }        }        if (selector != null) {            try {                selector.close();            } catch (IOException e) {                e.printStackTrace();            }        }    }    private void handleInput(SelectionKey key) throws IOException {        SocketChannel sc= (SocketChannel) key.channel();        if (key.isConnectable()) {            if (sc.finishConnect()) {                sc.register(selector, SelectionKey.OP_READ);                doWrite(sc);            }else                System.exit(1);        }        if (key.isReadable()) {            ByteBuffer readBuffer = ByteBuffer.allocate(1024);            int readBytes = sc.read(readBuffer);            if (readBytes > 0) {                readBuffer.flip();                byte[] bytes = new byte[readBuffer.remaining()];                readBuffer.get(bytes);                String body = new String((bytes), "UTF-8");                System.out.println("--接收到消息:" + body);                this.stop=true;            } else if (readBytes < 0) {                //对面关掉了链接                key.cancel();                sc.close();            }else                ;  //没有读到东西        }    }    private void doConnect() throws IOException {        //客户端去连接服务器，如果返回false，则说明发送了syn，但服务器没有响应ack，三次握手没有完成        if (socketChannel.connect(new InetSocketAddress(host, port))) {            socketChannel.register(selector, SelectionKey.OP_READ);            doWrite(socketChannel);        } else {            //如果没有直连成功，则新建连接            socketChannel.register(selector, SelectionKey.OP_CONNECT);        }    }    private void doWrite(SocketChannel sc) throws IOException {        byte[] req="QUERY_TIME".getBytes();        ByteBuffer writeBuffer = ByteBuffer.allocate(req.length);        writeBuffer.put(req);        writeBuffer.flip();        sc.write(writeBuffer);        if (!writeBuffer.hasRemaining()) {            System.out.println("指令发送成功！");        }    }}