群聊案例

• 简介

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)

• 编写服务端

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();
    }
}

• 编写客户端

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, 每个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);
        }
    }
    
}

• 测试：先启动服务端，再启动2个客户端
  

• 在1个客户端中发送消息，其他客户端可以接收