TCP Server Handshake

```java
package com.ddhigh.learn;

import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;

public class Main {
    public static void main(String[] args) throws Exception {
        ServerSocket ss = new ServerSocket(10000, 128);
        System.out.println("listen on port: 10000. backlog=128");
        while (true) {
            Socket s = ss.accept();
            Thread t = new Thread(new ClientThread(s));
            t.start();
        }
    }

    static class ClientThread implements Runnable {
        private Socket client;

        public ClientThread(Socket client) {
            this.client = client;
        }

        @Override
        public void run() {
            System.out.printf("[Thread-%s] %s connected\n", Thread.currentThread().getName(), client.getRemoteSocketAddress());
            try (
                    BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(client.getOutputStream()));
                    BufferedReader br = new BufferedReader(new InputStreamReader(client.getInputStream()))
            ) {
                this.handshake(bw, br);
                // 开始正常逻辑交互
                bw.write("HELLO WORLD!\n");
                bw.flush();
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                System.out.printf("[Thread-%s] %s disconnected\n", Thread.currentThread().getName(), client.getRemoteSocketAddress());
            }
        }

        /**
         * 握手
         *
         * @param bw
         * @param br
         * @throws IOException
         */
        private void handshake(BufferedWriter bw, BufferedReader br) throws IOException {
            // 检测账号
            while (true) {
                bw.write("username:\n");
                bw.flush();
                String username = br.readLine();
                if (username.isEmpty() || !username.equals("xialei")) {
                    bw.write("username invalid.\n");
                    bw.flush();
                    continue;
                }
                break;
            }

            // 检测密码
            while (true) {
                bw.write("password:\n");
                bw.flush();
                String password = br.readLine();
                if (password.isEmpty() || !password.equals("111111")) {
                    bw.write("password invalid.\n");
                    bw.flush();
                    continue;
                }
                break;
            }
            // 握手完成
            bw.write("handshake ok\n");
            bw.flush();
        }
    }
}
```