NIO Server

package com.shengsiyuan.nio;

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.nio.charset.Charset;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import java.util.UUID;

public class NioServer {

    private static Map<String, SocketChannel> clientMap = new HashMap();

    public static void main(String[] args) throws IOException {
        ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();//创建一个ServerSocketChannel
        serverSocketChannel.configureBlocking(false);//非阻塞
        ServerSocket serverSocket = serverSocketChannel.socket();//通过服务端的channel获取服务端的socket,
        serverSocket.bind(new InetSocketAddress(8899));

        Selector selector = Selector.open();//服务端channel注册到选择器上，
        //选择器可以关联多个channel对象，这里只有一个channel。
        serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);//现在关注服务端channel的连接事件，

        while (true) {
            try {//异常try()catch{}
                selector.select();//阻塞，等着关注的事件发生，返回发生的关注事件的数量。

                Set<SelectionKey> selectionKeys = selector.selectedKeys();//一个个的事件，现在只有一个OP_ACCEPT事件，

                selectionKeys.forEach(selectionKey -> {
                    final SocketChannel client;

                    try {
                        //OP_ACCEPT事件
                        if (selectionKey.isAcceptable()) {
                            //这个selectionKey关联的channel是服务端channel，OP_ACCEPT是服务端channel关注的事件（并注册在选择器上）
                            //所以这里可以强制转为服务端channel，
                            ServerSocketChannel server = (ServerSocketChannel) selectionKey.channel();
                            client = server.accept();//接受连接，真正接收连接之后返回SocketChannel对象，就是与客户端通信的socket，
                            //对于当前通道，服务端socket就用不上了，用SocketChannel
                            client.configureBlocking(false);//非阻塞的
                            //转而把SocketChannel注册到选择器，并关注读事件，
                            client.register(selector, SelectionKey.OP_READ);
                            //此时这个选择器有2个socket，一个服务端channel一个SocketChannel，一个关注连接一个关注数据读取，
                            String key = "【" + UUID.randomUUID().toString() + "】";

                            clientMap.put(key, client);

                        //OP_READ事件
                        } else if (selectionKey.isReadable()) {
                            client = (SocketChannel) selectionKey.channel();//肯定是客户端关联的socket
                            ByteBuffer readBuffer = ByteBuffer.allocate(1024);

                            int count = client.read(readBuffer);//读到buffer

                            if (count > 0) {
                                readBuffer.flip();

                                Charset charset = Charset.forName("utf-8");//编码
                                //发过来的数据转成string
                                String receivedMessage = String.valueOf(charset.decode(readBuffer).array());
                                //打印客户端发过来的数据
                                System.out.println(client + ": " + receivedMessage);

                                String senderKey = null;

                                for (Map.Entry<String, SocketChannel> entry : clientMap.entrySet()) {
                                    if (client == entry.getValue()) {
                                        senderKey = entry.getKey();
                                        break;
                                    }
                                }

                                for (Map.Entry<String, SocketChannel> entry : clientMap.entrySet()) {
                                    SocketChannel value = entry.getValue();
                                    //先写到ByteBuffer
                                    ByteBuffer writeBuffer = ByteBuffer.allocate(1024);
                                    writeBuffer.put((senderKey + ": " + receivedMessage).getBytes());

                                    writeBuffer.flip();
                                    //然后buteBuffer写出去到channel
                                    value.write(writeBuffer);
                                }
                            }
                        }
                    } catch (Exception ex) {
                        ex.printStackTrace();
                    }
                });

                selectionKeys.clear();//事件处理完成之后要清空，否则下次还要处理，就会报空指针。就是iter.remove();
            } catch (Exception ex) {
                ex.printStackTrace();
            }
        }
    }
}

package com.shengsiyuan.nio;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
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.time.LocalDateTime;
import java.util.Set;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class NioClient {

    public static void main(String[] args) throws IOException {
        try {
            SocketChannel socketChannel = SocketChannel.open();//@587
            socketChannel.configureBlocking(false);

            Selector selector = Selector.open();
            //OP_ACCEPT是接受连接，OP_CONNECT是发起连接，
            socketChannel.register(selector, SelectionKey.OP_CONNECT);
            socketChannel.connect(new InetSocketAddress("127.0.0.1", 8899));

            while (true) {
                selector.select();//阻塞
                Set<SelectionKey> keySet = selector.selectedKeys();

                for (SelectionKey selectionKey : keySet) {
                    //已经建立好了连接
                    if (selectionKey.isConnectable()) {
                        SocketChannel client = (SocketChannel) selectionKey.channel();//就是之前的那个socket @587
                        //连接是否处于进行状态
                        if (client.isConnectionPending()) {
                            client.finishConnect();//完成连接，现在连接真正建立好了，
                            //向服务器发送连接建立好了的消息
                            ByteBuffer writeBuffer = ByteBuffer.allocate(1024);
                            writeBuffer.put((LocalDateTime.now() + " 连接成功").getBytes());
                            //翻转
                            writeBuffer.flip();
                            //写到channel
                            client.write(writeBuffer);

                            ExecutorService executorService = Executors.newSingleThreadExecutor(
                                    Executors.defaultThreadFactory());//只有一个线程的线程池
                            executorService.submit(() -> {
                                while (true) {
                                    try {
                                        writeBuffer.clear();
                                        InputStreamReader input = new InputStreamReader(System.in);
                                        BufferedReader br = new BufferedReader(input);
                                        String sendMessage = br.readLine();
                                        //写入到buffer
                                        writeBuffer.put(sendMessage.getBytes());
                                        //翻转
                                        writeBuffer.flip();
                                        //buffer写出去
                                        client.write(writeBuffer);
                                    } catch (Exception ex) {
                                        ex.printStackTrace();
                                    }
                                }
                            });
                        }
                        //给这个channel注册读取事件，
                        client.register(selector, SelectionKey.OP_READ);//@587
                    } else if (selectionKey.isReadable()) {
                        SocketChannel client = (SocketChannel) selectionKey.channel();//@587
                        ByteBuffer readBuffer = ByteBuffer.allocate(1024);
                        int count = client.read(readBuffer);
                        if (count > 0) {
                            String receivedMessage = new String(readBuffer.array(), 0, count);//字节数组转字符串
                            System.out.println(receivedMessage);
                        }
                    }
                }
                keySet.clear();//清除事件，就是清除SelectionKey集合。
            }
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
}