一、前言

通过NIO编写简单版聊天室，客户端通过控制台输入发送消息到其他客户端。注意：并未处理粘包半包问题。

二、逻辑简述

服务器：

1）创建服务器NIO通道，绑定端口并启动服务器
2）开启非阻塞模式
3）创建选择器、并把通道注册到选择器上，关心的事件为新连接
4）循环监听选择器的事件，
5）监听到新连接事件：5.1） 建立连接、创建客户端通道5.2）客户端通道设置非阻塞5.3）客户端注册到选择器上，关心的事件为读
6）监听到读 事件6.1）获取到发送数据的客户端通道6.2）把通道数据写入到一个缓冲区中6.3）打印数据6.4）发送给其他注册在选择器上的客户端，排除自己

客户器：

1）创建客户端通道，连接服务器 ip和端口
2）创建选择器，注册客户端通道到选择器上，关心的事件为读
3）开启一个线程 循环监听选择器事件
4）监听到读事件后4.1）从通道中把数据读到缓冲区中4.2）打印数据
5）主线程循环用scanner 来监听控制台输入5.1）有输入后 发送给服务器

三、代码

服务器：

 
import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.*;
import java.util.Iterator;
import java.util.Set;/***/
public class GroupChatServer {private int port = 8888;private ServerSocketChannel serverSocketChannel;private Selector selector;public GroupChatServer() throws IOException {serverSocketChannel = ServerSocketChannel.open();serverSocketChannel.configureBlocking(false);serverSocketChannel.bind(new InetSocketAddress(port));//创建选择器selector = Selector.open();//通道注册到选择器上，关心的事件为 OP_ACCEPT：新连接serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);System.out.println("server is ok");}public void listener() throws IOException {for (; ; ) {if (selector.select() == 0) {continue;}//监听到时间Set<SelectionKey> selectionKeys = selector.selectedKeys();Iterator<SelectionKey> iterator = selectionKeys.iterator();while (iterator.hasNext()) {SelectionKey selectionKey = iterator.next();if (selectionKey.isAcceptable()) {//新连接事件newConnection();}if (selectionKey.isReadable()) {//客户端消息事件clientMsg(selectionKey);}iterator.remove();}}}/*** 客户端消息处理*/private void clientMsg(SelectionKey selectionKey) throws IOException {SocketChannel socketChannel = (SocketChannel) selectionKey.channel();ByteBuffer byteBuffer = (ByteBuffer) selectionKey.attachment();try {//通道数据读取到 byteBuffer缓冲区socketChannel.read(byteBuffer);//创建一个数组用于接受 缓冲区的本次写入的数据。byte[] bytes = new byte[byteBuffer.limit()];//转换模式 写->读byteBuffer.flip();//获取数据到 bytes 中 从位置0开始到limit结束byteBuffer.get(bytes, 0, byteBuffer.limit());String msg = socketChannel.getRemoteAddress() + "说：" + new String(bytes, "utf-8");//倒带这个缓冲区。位置设置为零，标记为-1.这样下次写入数据会从0开始写。但是如果下次的数据比这次少。那么使用 byteBuffer.array方法返回的byte数组数据会包含上一次的部分数据//例如 上次写入了 11111 倒带后 下次写入了 22 读取出来 却是 22111byteBuffer.rewind();System.out.println(msg);//发送给其他客户端sendOuterClient(msg, socketChannel);} catch (Exception e) {System.out.println(socketChannel.getRemoteAddress() + ":下线了");socketChannel.close();}}/*** 发送给其他客户端** @param msg           要发送的消息* @param socketChannel 要排除的客户端* @throws IOException*/private void sendOuterClient(String msg, SocketChannel socketChannel) throws IOException {//获取selector上注册的全部通道集合Set<SelectionKey> keys = selector.keys();for (SelectionKey key : keys) {SelectableChannel channel = key.channel();//判断通道是客户端通道（因为服务器的通道也注册在该选择器上），并且排除发送人的通道if (channel instanceof SocketChannel && !channel.equals(socketChannel)) {try {((SocketChannel) channel).write(ByteBuffer.wrap(msg.getBytes()));} catch (Exception e) {channel.close();System.out.println(((SocketChannel) channel).getRemoteAddress() + "：已下线");}}}}/*** 新连接处理方法* @throws IOException*/private void newConnection() throws IOException {//连接获取SocketChannelSocketChannel socketChannel = serverSocketChannel.accept();//设置非阻塞socketChannel.configureBlocking(false);//注册到选择器上，关心的事件是读，并附带一个ByteBuffer对象socketChannel.register(selector, SelectionKey.OP_READ, ByteBuffer.allocate(1024));System.out.println(socketChannel.getRemoteAddress() + " 上线了");}public static void main(String[] args) throws IOException {GroupChatServer groupChatServer = new GroupChatServer();//启动监听groupChatServer.listener();}
}

客户端：

 
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.Scanner;
import java.util.Set;/**    */
public class GroupChatClient {private Selector selector;private SocketChannel socketChannel;public GroupChatClient(String host, int port) throws IOException {socketChannel = SocketChannel.open(new InetSocketAddress(host, port));socketChannel.configureBlocking(false);selector = Selector.open();//注册事件，关心读事件socketChannel.register(selector, SelectionKey.OP_READ);System.out.println("我是：" + socketChannel.getLocalAddress());}/*** 读消息*/private void read() {try {if(selector.select() == 0){//没有事件，returnreturn;}Set<SelectionKey> selectionKeys = selector.selectedKeys();Iterator<SelectionKey> iterator = selectionKeys.iterator();while (iterator.hasNext()){SelectionKey selectionKey = iterator.next();if(selectionKey.isReadable()){//判断是 读 事件SocketChannel socketChannel = (SocketChannel)selectionKey.channel();ByteBuffer byteBuffer = ByteBuffer.allocate(1024);//读取数据到  byteBuffer 缓冲区socketChannel.read(byteBuffer);//打印数据System.out.println(new String(byteBuffer.array()));}iterator.remove();}} catch (IOException e) {e.printStackTrace();}}/*** 发送数据* @param msg 消息* @throws IOException*/private void send(String msg) throws IOException {socketChannel.write(ByteBuffer.wrap(new String(msg.getBytes(),"utf-8").getBytes()));}public static void main(String[] args) throws IOException {//创建客户端 指定 ip端口GroupChatClient groupChatClient = new GroupChatClient("127.0.0.1",8888);//启动一个线程来读取数据new Thread(()->{while (true){groupChatClient.read();}}).start();//Scanner 发送数据Scanner scanner = new Scanner(System.in);while (scanner.hasNextLine()){String s = scanner.nextLine();//发送数据groupChatClient.send(s);}}
}