Java でフォーム データへの同時アクセスと競合状態を処理するにはどうすればよいですか?

public class User {
    private String username;
    private String password;
    
    // 省略构造函数和getter/setter方法
}

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.atomic.AtomicInteger;

public class UserService {
    private Map<String, User> users = new HashMap<>();
    private AtomicInteger count = new AtomicInteger(0);
    
    public boolean registerUser(String username, String password) {
        // 检查账号是否已被注册
        if (users.containsKey(username)) {
            return false;
        }
        
        // 模拟注册需要一定时间
        try {
            Thread.sleep(100);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        
        // 创建新用户并添加到注册用户列表
        User user = new User(username, password);
        users.put(username, user);
        count.incrementAndGet();
        
        return true;
    }
    
    public int getUserCount() {
        return count.get();
    }
}

public class Main {
    public static void main(String[] args) {
        final UserService userService = new UserService();
        
        // 创建10个模拟用户注册的线程
        for (int i = 0; i < 10; i++) {
            final int index = i;
            new Thread(() -> {
                String username = "user" + index;
                String password = "password" + index;
                
                boolean success = userService.registerUser(username, password);
                if (success) {
                    System.out.println("User " + username + " registered successfully!");
                    System.out.println("Total registered user count: " + userService.getUserCount());
                } else {
                    System.out.println("User " + username + " registration failed!");
                }
            }).start();
        }
    }
}