Java入力チェックの基本と実践12選！初心者向けプログラミング徹底ガイド

public class InputCheckExample {
    public static void main(String[] args) {
        String userInput = args.length > 0 ? args[0] : "guest";
        String unsafeQuery = "SELECT * FROM users WHERE username='" + userInput + "'";
        String safeQuery = "SELECT * FROM users WHERE username=?";
        System.out.println(unsafeQuery);
        System.out.println(safeQuery);
    }
}

import java.util.regex.Pattern;

public class UserExperienceExample {
    public static void main(String[] args) {
        String emailInput = args.length > 0 ? args[0] : "sample@example.com";
        Pattern pattern = Pattern.compile("^[A-Za-z0-9+_.-]+@[A-Za-z0-9.-]+$");
        if (pattern.matcher(emailInput).matches()) {
            System.out.println("有効なメールアドレスです");
        } else {
            System.out.println("メールアドレスの形式で入力してください");
        }
    }
}

public class StringBlankCheck {
    public static void main(String[] args) {
        String input = "Hello World";
        if (input.isBlank()) {
            System.out.println("文字列は空白です");
        } else {
            System.out.println("文字列は入力されています");
        }
    }
}

public class StringLengthCheck {
    public static void main(String[] args) {
        String input = "Hello World";
        if (input.length() > 10) {
            System.out.println("文字列は10文字を超えています");
        } else {
            System.out.println("文字列は10文字以内です");
        }
    }
}

public class PositiveNumberCheck {
    public static void main(String[] args) {
        int number = 5;
        if (number >= 0) {
            System.out.println("数値は0以上です");
        } else {
            System.out.println("数値は負数です");
        }
    }
}

public class NumberRangeCheck {
    public static void main(String[] args) {
        int number = 5;
        if (number >= 1 && number <= 10) {
            System.out.println("数値は1から10の範囲内です");
        } else {
            System.out.println("数値は1から10の範囲外です");
        }
    }
}

import java.util.regex.Pattern;

public class EmailValidation {
    public static void main(String[] args) {
        String email = "test@example.com";
        System.out.println(validateEmailAddress(email));
    }

    public static boolean validateEmailAddress(String email) {
        String emailPattern = "^[a-zA-Z0-9_.+-]+@[a-zA-Z0-9-]+\.[a-zA-Z0-9-.]+$";
        return Pattern.compile(emailPattern).matcher(email).matches();
    }
}

public class PasswordStrengthChecker {
    public static void main(String[] args) {
        String password = "Aa1@bcdef";
        boolean isLongEnough = password.length() >= 8;
        boolean hasUppercase = password.matches(".*[A-Z].*");
        boolean hasLowercase = password.matches(".*[a-z].*");
        boolean hasDigit = password.matches(".*\d.*");
        boolean hasSpecialChar = password.matches(".*[!@#\$%^&*].*");

        if (isLongEnough && hasUppercase && hasLowercase && hasDigit && hasSpecialChar) {
            System.out.println("パスワードは基準を満たしています");
        } else {
            System.out.println("パスワードが基準を満たしていません");
        }
    }
}

import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.time.format.DateTimeParseException;

public class DateCheck {
    public static void main(String[] args) {
        String inputDate = "2023/09/12";
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("uuuu/MM/dd");
        try {
            LocalDate.parse(inputDate, formatter);
            System.out.println("日付の形式が正しいです");
        } catch (DateTimeParseException e) {
            System.out.println("日付の形式が不正です");
        }
    }
}

import java.net.URI;

public class URLValidator {
    public static void main(String[] args) {
        String url = "https://www.example.com";
        System.out.println("URLが有効かどうか: " + validateURL(url));
    }

    public static boolean validateURL(String url) {
        try {
            URI uri = URI.create(url);
            String scheme = uri.getScheme();
            return ("http".equals(scheme) || "https".equals(scheme)) && uri.getHost() != null;
        } catch (IllegalArgumentException e) {
            return false;
        }
    }
}

public class PhoneNumberValidation {
    public static void main(String[] args) {
        String phoneNumber = "090-1234-5678";
        if (validatePhoneNumber(phoneNumber)) {
            System.out.println("電話番号の形式が正しいです");
        } else {
            System.out.println("電話番号の形式が正しくありません");
        }
    }

    public static boolean validatePhoneNumber(String phoneNumber) {
        return phoneNumber.matches("^0\d{1,4}-\d{1,4}-\d{4}$");
    }
}

public class CreditCardNumberValidator {
    public static void main(String[] args) {
        String cardNumber = "1234 5678 1234 5678";
        if (isValidCardNumber(cardNumber)) {
            System.out.println("クレジットカード番号は形式上有効です");
        } else {
            System.out.println("クレジットカード番号は形式上無効です");
        }
    }

    public static boolean isValidCardNumber(String cardNumber) {
        return cardNumber.matches("^[0-9]{4} [0-9]{4} [0-9]{4} [0-9]{4}$");
    }
}

public class PostalCodeValidator {
    public boolean validate(String postalCode) {
        return postalCode.matches("^[0-9]{3}-[0-9]{4}$");
    }

    public static void main(String[] args) {
        PostalCodeValidator validator = new PostalCodeValidator();
        System.out.println(validator.validate("123-4567"));
        System.out.println(validator.validate("123-45678"));
    }
}

public class ZenkakuCheck {
    public static void main(String[] args) {
        String input = "こんにちは";
        if (input.matches("^[\p{InCJKUnifiedIdeographs}\p{InHiragana}\p{InKatakana}\p{InHalfwidthAndFullwidthForms}]+$")) {
            System.out.println("全角文字のみで構成されています");
        } else {
            System.out.println("全角文字以外の文字が含まれています");
        }
    }
}

import java.util.Scanner;

public class ZenkakuInputCheck {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("文字列を入力してください: ");
        String input = scanner.nextLine();
        if (input.matches("^[\p{InCJKUnifiedIdeographs}\p{InHiragana}\p{InKatakana}\p{InHalfwidthAndFullwidthForms}]+$")) {
            System.out.println("全角文字のみで構成されています");
        } else {
            System.out.println("全角文字以外の文字が含まれています");
        }
        scanner.close();
    }
}

public class HalfWidthCharacterChecker {
    public static void main(String[] args) {
        String input = "Hello12345";
        if (isHalfWidthCharacters(input)) {
            System.out.println("入力された文字列は半角文字のみです");
        } else {
            System.out.println("入力された文字列に全角文字が含まれています");
        }
    }

    public static boolean isHalfWidthCharacters(String input) {
        return input.matches("^[\x20-\x7E]+$");
    }
}

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class SQLInjectionPrevention {
    public static void main(String[] args) {
        String url = "jdbc:your-database-url";
        String user = "your-user";
        String password = "your-password";
        String userInput = "alice";
        String sql = "SELECT * FROM users WHERE username = ?";

        try (Connection conn = DriverManager.getConnection(url, user, password);
             PreparedStatement pstmt = conn.prepareStatement(sql)) {
            pstmt.setString(1, userInput);
            try (ResultSet rs = pstmt.executeQuery()) {
                while (rs.next()) {
                    System.out.println("ユーザー名: " + rs.getString("username"));
                    System.out.println("メール: " + rs.getString("email"));
                }
            }
        } catch (SQLException e) {
            System.out.println("データベース処理でエラーが発生しました");
        }
    }
}

public class HtmlEscapeSample {
    public static String escapeHtml(String input) {
        if (input == null) {
            return null;
        }
        return input.replace("&", "&")
                    .replace("<", "&lt;")
                    .replace(">", "&gt;")
                    .replace(""", "&quot;")
                    .replace("'", "&#x27;");
    }
}

public class HtmlEscapeRun {
    public static void main(String[] args) {
        String userInput = "<script>alert('XSS Attack!');</script>";
        String escapedInput = HtmlEscapeSample.escapeHtml(userInput);
        System.out.println("Escaped Input: " + escapedInput);
    }
}

@WebServlet("/csrftest")
public class CSRFProtectionServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String sessionToken = (String) request.getSession().getAttribute("CSRF_TOKEN");
        String requestToken = request.getParameter("CSRF_TOKEN");

        if (sessionToken != null && sessionToken.equals(requestToken)) {
            response.getWriter().write("request accepted");
        } else {
            response.sendError(HttpServletResponse.SC_FORBIDDEN, "CSRF protection token does not match");
        }
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String csrfToken = UUID.randomUUID().toString();
        request.getSession().setAttribute("CSRF_TOKEN", csrfToken);
        request.setAttribute("CSRF_TOKEN", csrfToken);
        request.getRequestDispatcher("/WEB-INF/jsp/csrftest.jsp").forward(request, response);
    }
}

<form action="csrftest" method="post">
    <input type="hidden" name="CSRF_TOKEN" value="${CSRF_TOKEN}">
    <input type="submit" value="Submit">
</form>

public class TrimExample {
    public static void main(String[] args) {
        String userInput = "  sample@email.com  ";
        String normalized = userInput.trim();
        System.out.println(normalized);
    }
}

import org.apache.commons.text.StringEscapeUtils;

public class EscapeLibraryExample {
    public static void main(String[] args) {
        String userInput = "<script>alert('XSS');</script>";
        String safeInput = StringEscapeUtils.escapeHtml4(userInput);
        System.out.println(safeInput);
    }
}

class InvalidInputException extends Exception {
    InvalidInputException(String message) {
        super(message);
    }
}

public class ErrorMessageExample {
    public static void main(String[] args) {
        try {
            throw new InvalidInputException("invalid email");
        } catch (InvalidInputException e) {
            System.out.println("入力内容を確認してください。メールアドレスの形式で入力してください。");
        }
    }
}

import jakarta.validation.Validation;
import jakarta.validation.Validator;
import jakarta.validation.constraints.Email;
import jakarta.validation.constraints.NotBlank;

public class Sample {
    public static class User {
        @NotBlank(message = "メールアドレスを入力してください。")
        @Email(message = "有効なメールアドレスを入力してください。")
        private String email;

        public void setEmail(String email) {
            this.email = email;
        }
    }

    public static void main(String[] args) {
        Validator validator = Validation.buildDefaultValidatorFactory().getValidator();
        User user = new User();
        user.setEmail("不正なメールアドレス");
        validator.validate(user).forEach(violation -> System.out.println(violation.getMessage()));
    }
}

import jakarta.validation.Constraint;
import jakarta.validation.ConstraintValidator;
import jakarta.validation.ConstraintValidatorContext;
import jakarta.validation.Payload;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

@Constraint(validatedBy = CustomValidator.MyConstraintValidator.class)
@Retention(RetentionPolicy.RUNTIME)
public @interface CustomValidator {
    String message() default "カスタムのバリデーションメッセージ";
    Class<?>[] groups() default {};
    Class<? extends Payload>[] payload() default {};

    class MyConstraintValidator implements ConstraintValidator<CustomValidator, String> {
        @Override
        public boolean isValid(String value, ConstraintValidatorContext context) {
            return value != null && value.matches("^[A-Z]{3}-[0-9]{4}$");
        }
    }
}