Java NIO如何实现群聊系统

这期内容当中小编将会给大家带来有关Java NIO如何实现群聊系统，文章内容丰富且以专业的角度为大家分析和叙述，阅读完这篇文章希望大家可以有所收获。

实例要求：

1）编写一个 Nio 群聊系统，实现服务器端和客户端之间的数据简单通讯（非阻塞）
2）实现多人群聊
3）服务器端：可以监测用户上线，离线，并实现消息转发功能
4）客户端：通过channel 可以无阻塞发送消息给其它所有用户，同时可以接受其它用户发送的消息(有服务器转发得到)
5）目的：进一步理解NIO非阻塞网络编程机制

服务端代码：

import java.io.IOException;import java.net.InetSocketAddress;import java.nio.ByteBuffer;import java.nio.channels.*;import java.util.Iterator; public class GroupChatServer {    //定义属性    private Selector selector;    private ServerSocketChannel listenChannel;    private static final int PORT = 6667;     //构造器    //初始化工作    public GroupChatServer() {         try {            //得到选择器            selector = Selector.open();            //ServerSocketChannel            listenChannel =  ServerSocketChannel.open();            //绑定端口            listenChannel.socket().bind(new InetSocketAddress(PORT));            //设置非阻塞模式            listenChannel.configureBlocking(false);            //将该listenChannel 注册到selector            listenChannel.reGISter(selector, SelectionKey.OP_ACCEPT);         }catch (IOException e) {            e.printStackTrace();        }    }     //监听    public void listen() {         System.out.println("监听线程: " + Thread.currentThread().getName());        try {             //循环处理            while (true) {                 int count = selector.select();                if(count > 0) {//有事件处理                     //遍历得到selectionKey 集合                    Iterator<SelectionKey> iterator = selector.selectedKeys().iterator();                    while (iterator.hasNext()) {                        //取出selectionkey                        SelectionKey key = iterator.next();                         //监听到accept                        if(key.isAcceptable()) {                            SocketChannel sc = listenChannel.accept();                            sc.configureBlocking(false);                            //将该 sc 注册到seletor                            sc.register(selector, SelectionKey.OP_READ);                            //提示                            System.out.println(sc.getRemoteAddress() + " 上线 ");                        }                        if(key.isReadable()) { //通道发送read事件，即通道是可读的状态                            //处理读 (专门写方法..)                            readData(key);                        }                        //当前的key 删除，防止重复处理                        iterator.remove();                    }                 } else {                    System.out.println("等待....");                }            }         }catch (Exception e) {            e.printStackTrace();         }finally {            //发生异常处理....        }    }     //读取客户端消息    private void readData(SelectionKey key) {         //取到关联的channle        SocketChannel channel = null;         try {           //得到channel            channel = (SocketChannel) key.channel();            //创建buffer            ByteBuffer buffer = ByteBuffer.allocate(1024);             int count = channel.read(buffer);            //根据count的值做处理            if(count > 0) {                //把缓存区的数据转成字符串                String msg = new String(buffer.array());                //输出该消息                System.out.println("fORM 客户端: " + msg);                //向其它的客户端转发消息(去掉自己), 专门写一个方法来处理                sendInfoToOtherClients(msg, channel);            }         }catch (IOException e) {            try {                System.out.println(channel.getRemoteAddress() + " 离线了..");                //取消注册                key.cancel();                //关闭通道                channel.close();            }catch (IOException e2) {                e2.printStackTrace();;            }        }    }     //转发消息给其它客户(通道)    private void sendInfoToOtherClients(String msg, SocketChannel self ) throws  IOException{         System.out.println("服务器转发消息中...");        System.out.println("服务器转发数据给客户端线程: " + Thread.currentThread().getName());        //遍历 所有注册到selector 上的 SocketChannel,并排除 self        for(SelectionKey key: selector.keys()) {             //通过 key  取出对应的 SocketChannel            Channel targetChannel = key.channel();             //排除自己            if(targetChannel instanceof  SocketChannel && targetChannel != self) {                //转型                SocketChannel dest = (SocketChannel)targetChannel;                //将msg 存储到buffer                ByteBuffer buffer = ByteBuffer.wrap(msg.getBytes());                //将buffer 的数据写入 通道                dest.write(buffer);            }        }    }     public static void main(String[] args) {        //创建服务器对象        GroupChatServer groupChatServer = new GroupChatServer();        groupChatServer.listen();    }} //可以写一个Handlerclass MyHandler {    public void readData() {    }    public void sendInfoToOtherClients(){    }}

客户端代码：

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 {     //定义相关的属性    private final String HOST = "127.0.0.1"; // 服务器的ip    private final int PORT = 6667; //服务器端口    private Selector selector;    private SocketChannel socketChannel;    private String username;     //构造器, 完成初始化工作    public GroupChatClient() throws IOException {         selector = Selector.open();        //连接服务器        socketChannel = socketChannel.open(new InetSocketAddress("127.0.0.1", PORT));        //设置非阻塞        socketChannel.configureBlocking(false);        //将channel 注册到selector        socketChannel.register(selector, SelectionKey.OP_READ);        //得到username        username = socketChannel.getLocalAddress().toString().substring(1);        System.out.println(username + " is ok...");     }     //向服务器发送消息    public void sendInfo(String info) {         info = username + " 说：" + info;        try {            socketChannel.write(ByteBuffer.wrap(info.getBytes()));        }catch (IOException e) {            e.printStackTrace();        }    }     //读取从服务器端回复的消息    public void readInfo() {         try {             int readChannels = selector.select();            if(readChannels > 0) {//有可以用的通道                 Iterator<SelectionKey> iterator = selector.selectedKeys().iterator();                while (iterator.hasNext()) {                     SelectionKey key = iterator.next();                    if(key.isReadable()) {                        //得到相关的通道                       SocketChannel sc = (SocketChannel) key.channel();                       //得到一个Buffer                        ByteBuffer buffer = ByteBuffer.allocate(1024);                        //读取                        sc.read(buffer);                        //把读到的缓冲区的数据转成字符串                        String msg = new String(buffer.array());                        System.out.println(msg.trim());                    }                }                iterator.remove(); //删除当前的selectionKey, 防止重复操作            } else {                //System.out.println("没有可以用的通道...");            }         }catch (Exception e) {            e.printStackTrace();        }    }     public static void main(String[] args) throws Exception {         //启动我们客户端        GroupChatClient chatClient = new GroupChatClient();         //启动一个线程, 每隔3秒，读取从服务器发送数据        new Thread() {            public void run() {                 while (true) {                    chatClient.readInfo();                    try {                        Thread.currentThread().sleep(3000);                    }catch (InterruptedException e) {                        e.printStackTrace();                    }                }            }        }.start();         //发送数据给服务器端        Scanner scanner = new Scanner(System.in);         while (scanner.hasNextLine()) {            String s = scanner.nextLine();            chatClient.sendInfo(s);        }    }}

注意：必须设置通道为非阻塞，才能向Selector注册，否则报 java.nio.channels.IllegalBlockingModeException 错
注意：在客户端上要想获取得到服务端的数据，也需要注册在register上(监听读事件)

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