客户端代码如下：

    import java.io.*;        import java.net.*;        import java.util.Scanner;                public class SimpleChatClient {            BufferedReader reader;            PrintWriter writer;            Socket sock;                        public void go(){                System.out.println("客户端启动！");                setUpNetworking();                //发送数据到服务器                Scanner scanner=new Scanner(System.in);                String sendString=scanner.nextLine();                while(sendString!=null&&!sendString.equals("byebye")){                    writer.println(sendString);                    writer.flush();                    sendString=scanner.nextLine();                }                scanner.close();                System.out.println("客户端退出！");            }                        public void setUpNetworking(){                try {                    sock=new Socket("127.0.0.1",5000);                    InputStreamReader streamReader=new InputStreamReader(sock.getInputStream());                    reader=new BufferedReader(streamReader);                    writer=new PrintWriter(sock.getOutputStream());                    System.out.println("networking established");                } catch (IOException e) {                    // TODO Auto-generated catch block                    e.printStackTrace();                }            }                                        public static void main(String[] args) {                // TODO Auto-generated method stub                SimpleChatClient client=new SimpleChatClient();                client.go();            }                }  

    import java.io.*;        import java.net.*;        public class SimpleChatServer {             //内部类            public class ClientHandler implements Runnable{                BufferedReader reader;                Socket sock;                            public ClientHandler(Socket clientSocket){                    sock=clientSocket;                    InputStreamReader isReader;                    try {                           isReader = new InputStreamReader(sock.getInputStream());                        reader=new BufferedReader(isReader);                    } catch (IOException e) {                        // TODO Auto-generated catch block                        e.printStackTrace();                    }                                    }                   @Override                public void run() {                    // TODO Auto-generated method stub                    String messageString;                    try {                        while((messageString=reader.readLine())!=null){                            System.out.println("read "+messageString);                        }                    } catch (IOException e) {                        // TODO Auto-generated catch block                                      System.out.println("有一个连接断开");                    }                }                            }            public void go(){                System.out.println("服务器启动成功！");                ServerSocket serverSock;                try {                    serverSock = new ServerSocket(5000);                    while(true){                        Socket clientSocket=serverSock.accept();                        Thread thread=new Thread(new ClientHandler(clientSocket));                        thread.start();                        System.out.println("got a connection!");                    }                } catch (IOException e) {                    // TODO Auto-generated catch block                    e.printStackTrace();                }                            }                        public static void main(String[] args) {                // TODO Auto-generated method stub                new SimpleChatServer().go();            }                }