码农路上

首先启动TimeServer 服务端开始监听
其次启动TimeClient 连接服务端,并发送固定指令QUERY TIME ORDER查询当前时间
最后服务端返回当前时间

具体代码如下(可运行)

TimeServer.java

package club.wujingjian.com.wujingjian.nio.server;

public class TimeServer {

    public static void main(String[] args) {
        int port = 9090;

        if (args != null && args.length > 0) {
            try {
                port = Integer.parseInt(args[0]);
            } catch (NumberFormatException e) {
                e.printStackTrace();
            }
        }
        MultiplexerTimeServer timeServer = new MultiplexerTimeServer(port);

        new Thread(timeServer, "NIO-MultiplexerTimeServer-001").start();
    }
}

MultiplexerTimeServer.java

package club.wujingjian.com.wujingjian.nio.server;

import club.wujingjian.com.wujingjian.nio.Util;

import java.io.IOError;
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;

public class MultiplexerTimeServer implements  Runnable {

    private Selector selector;

    private ServerSocketChannel servChannel;

    private volatile  boolean stop;

    /**
     * 初始化多路复用器、绑定监听端口
     * 进行资源初始化,创建多路复用器Selector、ServerSocketChannel,
     * 对Channel和TCP参数进行配置,（例如,将ServerSocketChannel设置为异步非阻塞模式,它的backlog设置为1024）
     *
     */
    public MultiplexerTimeServer(int port) {
        try {
            selector = Selector.open();
            servChannel = ServerSocketChannel.open();
            servChannel.configureBlocking(false);
            servChannel.socket().bind(new InetSocketAddress(port), 1024);
            //将ServerSocketChannel注册到Selector,监听SelectionKey.OP_ACCEPT操作位
            servChannel.register(selector, SelectionKey.OP_ACCEPT);
            System.out.println(Util.nowDate() + "The time server is start in port : " + port);
        } catch (IOException e) {
            e.printStackTrace();;
            System.exit(1);
        }
    }

    public void stop(){
        this.stop = true;
    }
    @Override
    public void run() {
        while (!stop) {
            /**
             * 循环遍历selector,休眠时间为1s
             */
            try {
                selector.select(1000);
                Set<SelectionKey> selectedKeys = selector.selectedKeys();
                Iterator<SelectionKey> it = selectedKeys.iterator();
                SelectionKey key = null;
                while (it.hasNext()) {
                    key = it.next();
                    it.remove();
                    try {
                        handleInput(key);
                    } catch (Exception e) {
                        key.cancel();
                        if (key.channel() != null) {
                            key.channel().close();
                        }
                    }
                }
            } catch (Throwable throwable) {
                throwable.printStackTrace();
            }
        }

        //多路复用器关闭后,所有注册在上面的channel 和pipe 等资源都会被自动去注册并关闭,所以不需要重复释放资源
        if (selector != null) {
            try {
                selector.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }



    private void handleInput(SelectionKey key) throws  IOException {
        if (key.isValid()) {
            /**
             *处理新接入的客户端请求信息,根据SelectionKey的操作位进行判断即可获知网络事件的类型
             */
            if (key.isAcceptable()) {
                //接收新连接
                ServerSocketChannel ssc = (ServerSocketChannel) key.channel();
                //通过ServerSocketChannel的accept()接收客户端的连接请求并创建SocketChannel实例.相当于三次握手
                SocketChannel sc = ssc.accept();
                sc.configureBlocking(false);
                //添加新连接到多路复用器Selector
                sc.register(selector, SelectionKey.OP_READ);
            }
            if (key.isReadable()) {
                /**
                 * 读取客户端的请求消息,首先创建一个ByteBuffer,由于事先无法得知客户端发送的码流大小,作为例程，我们开辟一个1K的缓冲区，
                 * 然后调用SocketChannel的read方法读取请求码流.
                 * 注意: 由于我们已经将SocketChannel设置为异步非阻塞模式,因此他的read是非阻塞的,  socketChannel.read()的返回值有以下三种情况
                 *     返回值大于0:  读取到了字节,对字节进行编解码.
                 *     返回值等于0: 没有读取到字节,属于正常场景,忽略
                 *     返回值为-1 : 链路已经关闭,需要关闭SocketChannel,释放资源
                 */
                SocketChannel sc = (SocketChannel) key.channel();
                ByteBuffer readBuffer = ByteBuffer.allocate(1024);
                int readBytes = sc.read(readBuffer);
                if (readBytes > 0) {
                    //读取到码流以后,我们进行解码,首先对readBuffer进行flip操作,作用是将缓冲区当前的limit设置为position,position设置为0,用于后续对缓冲区的读取操作
                    readBuffer.flip();
                    //根据缓冲区可读的字节个数创建字节数组
                    byte[] bytes = new byte[readBuffer.remaining()];
                    //将缓冲区可读的字节数组复制到新创建的字节数组bytes中.
                    readBuffer.get(bytes);
                    String body = new String(bytes, "UTF-8");
                    System.out.println(Util.nowDate() + "The time server receive order : " + body);
                    //如果请求指令是"QUERY TIME ORDER" 则把服务器的当前时间编码后返回给客户端
                    String currentTime = "QUERY TIME ORDER".equalsIgnoreCase(body) ? new Date(System.currentTimeMillis()).toString() : "BAD ORDER";
                    System.out.println(Util.nowDate() + "服务器准备返回时间为 :" + currentTime);
                    doWrite(sc, currentTime);
                } else if (readBytes < 0) {
                    //对端链路关闭
                    key.cancel();
                    sc.close();
                } else{
                    // 读取到0字节,忽略
                }

            }
        }
    }

    private void doWrite(SocketChannel channel, String response) throws  IOException{
        if (response != null && response.trim().length() > 0) {
            //将字符串编码成字节数组,
            byte [] bytes = response.getBytes();
            //根据字节数组容量创建ByteBuffer
            ByteBuffer writeBuffer = ByteBuffer.allocate(bytes.length);
            //将字节数组复制到缓冲区中
            writeBuffer.put(bytes);
            //将缓冲区的position设置为0,以便准备输出
            writeBuffer.flip();
            /**
             *将缓冲区中的字节数组发送出去
             * 注意:    由于SocketChannel是异步非阻塞的,它并不能保证一次性把需要发送的字节数组发送完毕,此时会出现"写半包"的问题,
             *      我们需要注册写操作,不断轮询Selector将没有发送完的ByteBuffer发送完毕,可以通过ByteBuffer的hasRemaining()方法
             *      判断消息是否发送完成。此处仅仅是个入门示例,没有处理"写半包"的情况.
             */
            channel.write(writeBuffer);
            if (!writeBuffer.hasRemaining()) {
                System.out.println(Util.nowDate() + "发送成功");
            }
        }
    }
}

下面是客户端代码

TimeClient.java

package club.wujingjian.com.wujingjian.nio.client;

public class TimeClient {
    public static void main(String[] args) {
        int port = 9090;
        if (args != null && args.length > 0) {
            try {
                port = Integer.parseInt(args[0]);
            } catch (NumberFormatException e) {
                e.printStackTrace();
            }
        }
        new Thread(new TimeClientHandle("127.0.0.1",port), "TimeClient-001").start();
    }
}

TimeClientHandle.java

package club.wujingjian.com.wujingjian.nio.client;

import club.wujingjian.com.wujingjian.nio.Util;

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 TimeClientHandle implements Runnable {

    private String host;
    private int port ;
    private Selector selector;
    private SocketChannel socketChannel;
    private volatile boolean stop;

    /**
     * 构造函数初始化NIO多路复用器和SocketChannel对象，并将socketChannel设置为异步非阻塞模式
     * @param host
     * @param port
     */
    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 {
            //发送连接请求,作为示例,连接是成功的,所以不需要做重连操作,实际代码中,可能要考虑重连,不能放到while循环外面
            doConnect();
        } catch (IOException e) {
            e.printStackTrace();
            System.exit(1);
        }
        while (!stop) {
            try {
                selector.select(1000);
                Set<SelectionKey> selectedKeys = selector.selectedKeys();
                Iterator<SelectionKey> it = selectedKeys.iterator();
                SelectionKey key = null;
                //当有就绪的Channel时候执行handleInput方法
                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);
            }
        }

        //多路复用器关闭后,所有注册在上面的channel和pipe等资源都会被自动去注册并关闭,所以不需要重复释放资源
        if (selector != null) {
            try {
                selector.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    private void handleInput(SelectionKey key) throws  IOException {
        if (key.isValid()) {
            //判断是否连接成功
            SocketChannel sc = (SocketChannel) key.channel();
            if (key.isConnectable()) { //如果SelectionKey处于连接状态,说明服务端已经返回ACK应答消息,这是我们需要对结果进行判断
                if (sc.finishConnect()) { //如果sc.finishConnect()返回true,说明客户端连接成功,
                    System.out.println(Util.nowDate() + "客户端连接成功");
                    sc.register(selector, SelectionKey.OP_READ); //将SocketChannel注册到多路复用器上,注册SelectionKey.OP_READ操作位,监听网络读操作,
                    doWrite(sc); //然后发送请求消息给服务端
                } else {
                    System.out.println("连接失败,进程退出");
                    System.exit(1); //连接失败,进程退出
                }
            }

            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(Util.nowDate() + "Now is :" + body);
                    this.stop = true;
                } else if (readBytes < 0) {
                    //对端链路关闭
                    key.cancel();
                    sc.close();
                } else {
                    //读到0 字节,忽略
                }
            }
        }
    }

    private void doConnect() throws  IOException {
        //如果直连成功,则注册到多路复用器上,发送请求消息,读应答
        if (socketChannel.connect(new InetSocketAddress(host, port))) {
            socketChannel.register(selector, SelectionKey.OP_READ);
            doWrite(socketChannel);
        } else {
            /**
             * 如果没有直接连接成功,则说明服务端没有返回TPC握手应答消息,担这并不代表连接失败.
             * 我们需要将SocketChannel注册到多路复用器Selector上,注册SelectionKey.OP_CONNECT，
             * 当服务端返回TCP syn-ack消息后,Selector就能够轮询到这个SocketChannel处于连接就绪状态
             */
            socketChannel.register(selector, SelectionKey.OP_CONNECT);
        }
    }

    private void doWrite(SocketChannel sc) throws IOException {
        byte[] req = "QUERY TIME ORDER".getBytes();
        ByteBuffer writeBuffer = ByteBuffer.allocate(req.length);
        writeBuffer.put(req);
        writeBuffer.flip();
        sc.write(writeBuffer); //此时可能会存在"半包写"问题,实际工作中要考虑
        if (!writeBuffer.hasRemaining()) { //此时如果缓冲区中消息全部发送完成，打印如下消息Send order 2 server succeed.
            System.out.println(Util.nowDate() + "Send order 2 server succeed.");
        }
    }
}

先允许服务器端，后允许客户端代码最后输出分别为: