Java程序中用户输入验证与流程控制的最佳实践

import java.util.Scanner;

public class PasswordValidationTutorial {

    // 定义密码规则常量
    private static final int MIN_LENGTH = 8;
    private static final int MIN_UPPERCASE = 1;
    private static final int MIN_DIGITS = 1;
    private static final int MIN_SPECIAL_CHARS = 1;
    private static final int MAX_ATTEMPTS = 3; // 最大尝试次数

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.println("请填写您的个人信息：");

        System.out.print("请输入姓名: ");
        String name = scanner.nextLine();
        int spacePosition = name.indexOf(" "); // 用于后续生成用户名

        System.out.print("请输入生日 (MM DD YYYY): ");
        String birthday = scanner.nextLine();

        String password = "";
        boolean isValidPassword = false;
        int attemptCount = 0;

        // 使用while循环进行密码输入和验证
        while (!isValidPassword && attemptCount < MAX_ATTEMPTS) {
            System.out.print("\n请输入密码 (尝试次数: " + (attemptCount + 1) + "/" + MAX_ATTEMPTS + "): ");
            password = scanner.nextLine();

            // 调用密码验证方法
            isValidPassword = validatePassword(password);

            if (!isValidPassword) {
                attemptCount++;
                if (attemptCount < MAX_ATTEMPTS) {
                    System.out.println("密码不符合要求，请重新输入。");
                } else {
                    System.out.println("您已达到最大尝试次数。程序将终止。");
                    System.exit(1); // 终止程序，状态码为1表示异常退出
                }
            }
        }

        // 如果密码有效，则显示登录详情
        if (isValidPassword) {
            System.out.println("\n您的登录详情如下：");
            System.out.println("姓名    : " + name);
            System.out.println("生日    : " + birthday);
            // 假设的用户名生成逻辑
            String username = "";
            if (name.length() >= 2 && spacePosition != -1 && (spacePosition + 3) <= name.length() && birthday.length() >= 5) {
                username = name.substring(0, 2) + name.substring(spacePosition + 1, Math.min(spacePosition + 4, name.length())) + birthday.substring(3, 5);
            } else {
                username = name.replaceAll(" ", "") + birthday.substring(0, Math.min(birthday.length(), 5)); // 备用用户名生成
            }
            System.out.println("用户名: " + username);
            System.out.println("密码    : " + password);
        }

        scanner.close();
    }

    /**
     * 验证密码是否符合预设规则
     * @param password 待验证的密码字符串
     * @return 如果密码有效则返回 true，否则返回 false
     */
    private static boolean validatePassword(String password) {
        int uppercaseCounter = 0;
        int digitCounter = 0;
        int specialCounter = 0;
        int spaceCounter = 0;
        StringBuilder errorMessages = new StringBuilder(); // 用于收集错误信息

        // 遍历密码字符进行分类计数
        for (int i = 0; i < password.length(); i++) {
            char c = password.charAt(i);

            if (Character.isUpperCase(c)) {
                uppercaseCounter++;
            } else if (Character.isDigit(c)) {
                digitCounter++;
            } else if (c == ' ') {
                spaceCounter++;
            } else if ("$#?!_=%.".indexOf(c) != -1) { // 检查是否为定义的特殊字符
                specialCounter++;
            }
        }

        // 根据规则检查并收集错误信息
        boolean isValid = true;
        if (password.length() < MIN_LENGTH) {
            errorMessages.append("- 密码至少需要 ").append(MIN_LENGTH).append(" 个字符。\n");
            isValid = false;
        }
        if (spaceCounter > 0) {
            errorMessages.append("- 密码不能包含空格。\n");
            isValid = false;
        }
        if (uppercaseCounter < MIN_UPPERCASE) {
            errorMessages.append("- 密码至少需要 ").append(MIN_UPPERCASE).append(" 个大写字母。\n");
            isValid = false;
        }
        if (digitCounter < MIN_DIGITS) {
            errorMessages.append("- 密码至少需要 ").append(MIN_DIGITS).append(" 个数字。\n");
            isValid = false;
        }
        if (specialCounter < MIN_SPECIAL_CHARS) {
            errorMessages.append("- 密码至少需要 ").append(MIN_SPECIAL_CHARS).append(" 个特殊字符 ($#?!_=%.)。\n");
            isValid = false;
        }

        // 如果密码无效，打印所有错误信息
        if (!isValid) {
            System.out.println("密码验证失败：");
            System.out.print(errorMessages.toString());
        }

        return isValid;
    }
}

while (!isValidPassword && attemptCount < MAX_ATTEMPTS) { ... }