NIO系列：5.NIO群聊系统

谁践踏了优雅 2023-07-14 05:57 13阅读 0赞

前面的文章介绍了NIO的三大核心组件并编写了BIO的一个demo实例，本文使用NIO写一个小应用实例，巩固并加深对NIO的理解。

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Handler
    class 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)