设计一个登录验证系统，由用户名验证，密码验证和验证码验证三部分组成。当用户登录时，应该按照顺序执行这些验证器，如果有任意一个验证不通过，则认为登录失败。利用职责链接模式来实现这个应用场景。.用JAVA实现

好的，我理解了你的问题。这里是一个简单的实现，使用职责链模式确保每个验证器按顺序执行并决定是否通过验证。

首先，我们定义一个接口 `LoginValidator` 来表示验证器。它有两个方法：`setNext()` 和 `validate()`。`setNext()` 方法将下一个验证器链接到链中，`validate()` 方法执行实际的验证工作。

public interface LoginValidator {
    void setNext(LoginValidator nextValidator);
    boolean validate(LoginRequest request);
}

然后，我们实现三个具体的验证器：`UsernameValidator`，`PasswordValidator` 和 `CaptchaValidator`。每个验证器实现 `validate()` 方法，如果验证通过，则返回 `true`，否则返回 `false`。如果验证未通过，则不会调用下一个验证器。如果所有的验证器都通过了，那么登录才会成功。

public class UsernameValidator implements LoginValidator {
    private LoginValidator nextValidator;

    @Override
    public void setNext(LoginValidator nextValidator) {
        this.nextValidator = nextValidator;
    }

    @Override
    public boolean validate(LoginRequest request) {
        String username = request.getUsername();
        if (username == null || username.isEmpty()) {
            System.out.println("Username is empty");
            return false;
        }
        System.out.println("Username is validated");
        return nextValidator.validate(request);
    }
}

public class PasswordValidator implements LoginValidator {
    private LoginValidator nextValidator;

    @Override
    public void setNext(LoginValidator nextValidator) {
        this.nextValidator = nextValidator;
    }

    @Override
    public boolean validate(LoginRequest request) {
        String password = request.getPassword();
        if (password == null || password.isEmpty()) {
            System.out.println("Password is empty");
            return false;
        }
        System.out.println("Password is validated");
        return nextValidator.validate(request);
    }
}

public class CaptchaValidator implements LoginValidator {
    private LoginValidator nextValidator;

    @Override
    public void setNext(LoginValidator nextValidator) {
        this.nextValidator = nextValidator;
    }

    @Override
    public boolean validate(LoginRequest request) {
        String captcha = request.getCaptcha();
        if (captcha == null || captcha.isEmpty()) {
            System.out.println("Captcha is empty");
            return false;
        }
        System.out.println("Captcha is validated");
        return nextValidator.validate(request);
    }
}

最后，我们创建一个 `LoginRequest` 类来封装登录请求，并使用 `LoginValidator` 链来验证请求。当链中的验证器都通过时，认为登录成功。否则，认为登录失败。

public class LoginRequest {
    private String username;
    private String password;
    private String captcha;

    public LoginRequest(String username, String password, String captcha) {
        this.username = username;
        this.password = password;
        this.captcha = captcha;
    }

    public String getUsername() {
        return username;
    }

    public String getPassword() {
        return password;
    }

    public String getCaptcha() {
        return captcha;
    }

    public boolean login(LoginValidator validator) {
        return validator.validate(this);
    }
}

现在我们可以使用这些类来验证登录请求。首先，创建三个验证器实例，并将它们链接在一起：

LoginValidator validator = new UsernameValidator();
validator.setNext(new PasswordValidator());
validator.setNext(new CaptchaValidator());

然后，创建一个登录请求对象，并调用 `login()` 方法来验证请求。如果所有的验证器都通过了，那么登录就会成功。

LoginRequest request = new LoginRequest("user", "password", "captcha");
if (request.login(validator)) {
    System.out.println("Login succeeded");
} else {
    System.out.println("Login failed");
}

这里是完整的代码示例：

public interface LoginValidator {
    void setNext(LoginValidator nextValidator);
    boolean validate(LoginRequest request);
}

public class UsernameValidator implements LoginValidator {
    private LoginValidator nextValidator;

    @Override
    public void setNext(LoginValidator nextValidator) {
        this.nextValidator = nextValidator;
    }

    @Override
    public boolean validate(LoginRequest request) {
        String username = request.getUsername();
        if (username == null || username.isEmpty()) {
            System.out.println("Username is empty");
            return false;
        }
        System.out.println("Username is validated");
        return nextValidator.validate(request);
    }
}

public class PasswordValidator implements LoginValidator {
    private LoginValidator nextValidator;

    @Override
    public void setNext(LoginValidator nextValidator) {
        this.nextValidator = nextValidator;
    }

    @Override
    public boolean validate(LoginRequest request) {
        String password = request.getPassword();
        if (password == null || password.isEmpty()) {
            System.out.println("Password is empty");
            return false;
        }
        System.out.println("Password is validated");
        return nextValidator.validate(request);
    }
}

public class CaptchaValidator implements LoginValidator {
    private LoginValidator nextValidator;

    @Override
    public void setNext(LoginValidator nextValidator) {
        this.nextValidator = nextValidator;
    }

    @Override
    public boolean validate(LoginRequest request) {
        String captcha = request.getCaptcha();
        if (captcha == null || captcha.isEmpty()) {
            System.out.println("Captcha is empty");
            return false;
        }
        System.out.println("Captcha is validated");
        return nextValidator.validate(request);
    }
}

public class LoginRequest {
    private String username;
    private String password;
    private String captcha;

    public LoginRequest(String username, String password, String captcha) {
        this.username = username;
        this.password = password;
        this.captcha = captcha;
    }

    public String getUsername() {
        return username;
    }

    public String getPassword() {
        return password;
    }

    public String getCaptcha() {
        return captcha;
    }

    public boolean login(LoginValidator validator) {
        return validator.validate(this);
    }
}

public class Main {
    public static void main(String[] args) {
        LoginValidator validator = new UsernameValidator();
        validator.setNext(new PasswordValidator());
        validator.setNext(new CaptchaValidator());

        LoginRequest request = new LoginRequest("user", "password", "captcha");
        if (request.login(validator)) {
            System.out.println("Login succeeded");
        } else {
            System.out.println("Login failed");
        }
    }
}