3、nio中的selector使用

通过编写一个客户端和服务器端的例子来熟悉selector的使用

服务端逻辑：

1. 绑定一个端口号
2. channel注册到selector中
3. 用死循环来监听如果有时间发生，遍历selectionKey set
4. 判断发生的事件类型，前面会注册accept事件，如果发生accept事件，那么注册读事件，同时清除selectionKey set 中的当前元素。、
5. 接收事件时，将channel保存下来。
6. 发生读事件时，说明有信息，发过来了，那么将消息，转发给所有的客户端。然后清除自身的事件。

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.*;

public class NioServer {

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

    public static void main(String[] args) throws IOException {
        ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
        serverSocketChannel.configureBlocking(false);

        ServerSocket serverSocket = serverSocketChannel.socket();
        serverSocket.bind(new InetSocketAddress(8899));

        Selector selector = Selector.open();

        serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);

        while(true) {
            int number = selector.select();
//            System.out.println("number:" + number);
            Set<SelectionKey> selectionKeySet = selector.selectedKeys();

            Iterator<SelectionKey> iterable = selectionKeySet.iterator();

            if(number > 0 ) {
                while(iterable.hasNext()) {
                    SelectionKey selectionKey = iterable.next();

                    if(selectionKey.isAcceptable()) {//如果是可接收连接的
                        ServerSocketChannel ssc = (ServerSocketChannel) selectionKey.channel();
                        SocketChannel socketChannel = ssc.accept();
                        socketChannel.configureBlocking(false);

                        socketChannel.register(selector, SelectionKey.OP_READ);//注册读事件

                        clientMap.put(UUID.randomUUID() + "", socketChannel);//保存下channel

                        iterable.remove();
                    } else if(selectionKey.isReadable()){//可读的
                        SocketChannel socketChannel = (SocketChannel) selectionKey.channel();
                        ByteBuffer byteBuffer = ByteBuffer.allocate(1024);

                        int readCount = socketChannel.read(byteBuffer);

                        //这里本该用while
                        if(readCount > 0 ) {//读取到数据，就写回到其他客户端
                            byteBuffer.flip();

                            Charset charset = Charset.forName("UTF-8");
                            String receiveStr = new String(charset.decode(byteBuffer).array());

                            System.out.println(socketChannel + " receive msg :" + receiveStr);

                            String sendKey = "";

                            for(Map.Entry<String, SocketChannel> entry : clientMap.entrySet()) {//第一遍遍历找到发送者
                                if(socketChannel == entry.getValue()) {
                                    sendKey = entry.getKey();
                                    break;
                                }
                            }

                            for (Map.Entry<String, SocketChannel> entry: clientMap.entrySet()  ) {//给每个保存的连接，都发送消息
                                ByteBuffer writeBuffer = ByteBuffer.allocate(1024);
                                writeBuffer.put((sendKey + ":" +  receiveStr).getBytes());

                                writeBuffer.flip();
                                entry.getValue().write(writeBuffer);
                            }
                        }
                        iterable.remove();//这个 删除很关键  每次循环完selectionKeySet ，一定要清楚事件，不然肯定会影响下一次的事件触发，或者直接不触发下次的事件
                    }
                }
            }

        }
    }
}

客户端逻辑

1. 建立socketChannel 连接到对应的端口
2. 新建selector对象，然后把socketChannel注册到selector上
3. 建立死循环 ，监听是否有事件发生，若有，则遍历seletionKey set ,
4. 判断发生的事件是什么，
5. 如果是连接事件 ，做对应的连接处理，注册读事件

判断是否在等待连接 ，在进程中
if (channel.isConnectionPending()) { 
channel.finishConnect(); 完成连接，这里是阻塞的

6. 如果发生了读事件，读取数据

import java.io.BufferedReader;
import java.io.InputStream;
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.Iterator;
import java.util.Set;
import java.util.concurrent.Executor;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadFactory;

public class NioClient {

    public static void main(String[] args) {
        try{
            SocketChannel socketChannel = SocketChannel.open();
            socketChannel.configureBlocking(false);
            socketChannel.connect(new InetSocketAddress(8899));//服务端就是bind  然后accept  serverSocketChannel

            Selector selector = Selector.open();

            socketChannel.register(selector, SelectionKey.OP_CONNECT);//注册连接事件

            while(true) {
                int number = selector.select();

                if(number > 0) {
                    Set<SelectionKey> selectionKeySet =  selector.selectedKeys();

                    Iterator<SelectionKey> iterable = selectionKeySet.iterator();
                    while(iterable.hasNext()) {//有事件发生
                        SelectionKey selectionKey = iterable.next();

                        SocketChannel client = (SocketChannel) selectionKey.channel();
                        if(selectionKey.isConnectable()) {//判断 selectionkey 状态  可连接的
                            if(client.isConnectionPending()) {//是否在准备连接的进程中
                                client.finishConnect();//这里会阻塞，如果连接未建立，抛异常 ，

                                ByteBuffer byteBuffer = ByteBuffer.allocate(1024);

                                byteBuffer.put((LocalDateTime.now() + "，连接成功").getBytes());
                                byteBuffer.flip();
                                client.write(byteBuffer);

                                ExecutorService executorService = Executors.newSingleThreadExecutor(Executors.defaultThreadFactory());

                                executorService.submit(() -> {//起一个新的线程，去接收控制台的输入 ，不影响其他线程
                                    while(true) {
                                        try{
                                            byteBuffer.clear();
                                            InputStreamReader inputStreamReader = new InputStreamReader(System.in);
                                            BufferedReader bufferedReader = new BufferedReader(inputStreamReader);

                                            byteBuffer.put(bufferedReader.readLine().getBytes());
                                            byteBuffer.flip();
                                            client.write(byteBuffer);

                                        }catch (Exception e) {
                                            e.printStackTrace();
                                        }
                                    }
                                });
                            }

                            iterable.remove();//这个事件清楚，很关键
                            client.register(selector, SelectionKey.OP_READ);//注册读事件
                        } else if(selectionKey.isReadable()){//可读取
                            SocketChannel socketChannel1 = (SocketChannel) selectionKey.channel();
                            ByteBuffer readBuffer = ByteBuffer.allocate(1024);

                            int readCount = socketChannel.read(readBuffer);
                            if(readCount > 0) {
                                String receiveMsg = new String(readBuffer.array());
                                System.out.println("receiveMsg : " + receiveMsg);
                            }

                            iterable.remove();
                        }

                    }
                }
            }




        }catch (Exception e ) {
            e.printStackTrace();
        }


    }
}