CheckMate

CheckMate is a small Java validation library with:

• fluent validation chains
• reusable rules
• specialized validators (email, password, date)
• multiple errors (not only first error)
• map-based object validation

Requirements

• Java 17+
• Maven 3.9+

Quick start

git clone <your-fork-or-repo-url>
cd checkmate
mvn test

Core ideas

• Validator.of("...") or Validators.of("...") for generic fluent validation.
• Validators.email(...), Validators.password(...), Validators.date(...) for specialized validators.
• validate() returns boolean.
• validateResult() returns full ValidationResult with all collected messages.
• new Validator().addRule("field", rule) for map/payload validation by field.

Fluent API examples

Basic fluent chain

boolean valid = Validator.of("user@example.com")
        .isEmail()
        .isNotEmpty()
        .maxLength(50)
        .validate();

Collect multiple errors instead of first failure

import com.checkmate.core.ValidationResult;

ValidationResult result = Validators.password("abc")
        .isStrongPassword() // min length + digit + uppercase + special char
        .validateResult();

if (!result.isValid()) {
    System.out.println(result.getAllErrors());
}

Add a custom rule in chain

import com.checkmate.rules.common.RegexRule;

ValidationResult result = Validators.of("A!1")
        .minLength(8)
        .withRule(new RegexRule("^[A-Za-z0-9!@#$%^&*]+$", "contains invalid symbols"))
        .validateResult();

Specialized validators

Email

boolean ok = Validators.email("john.doe@example.com")
        .isNotEmpty()
        .isEmail()
        .maxLength(100)
        .validate();

Password

boolean strong = Validators.password("Strong!123")
        .isNotEmpty()
        .isStrongPassword()
        .validate();

You can also build rules step by step:

boolean strong = Validators.password("Strong!123")
        .minLength(10)
        .hasUpperCase()
        .hasDigit()
        .hasSpecialChar()
        .validate();

Phone (via generic fluent validator)

boolean validPhone = Validators.of("+380501112233")
        .isPhone()
        .minLength(10)
        .maxLength(15)
        .validate();

Date validation

Date validation is date-only in current MVP (no time part).

1) Accept any known date format

boolean valid = Validators.date("10 Apr 2026")
        .hasDateFormat()
        .validate();

Known supported patterns:

• yyyy-MM-dd (ISO)
• yyyy-MMM-dd
• dd-MM-yyyy
• dd/MM/yyyy
• MM/dd/yyyy
• dd.MM.yyyy
• dd MMM yyyy
• MMM dd, yyyy
• MMMM dd, yyyy
• dd MMMM yyyy

2) Require one specific pattern

boolean valid = Validators.date("10/04/2026")
        .hasDateFormat("dd/MM/yyyy")
        .validate();

3) Past and future checks

boolean isPast = Validators.date("01/01/2000")
        .isPastDate("dd/MM/yyyy")
        .validate();

boolean isFuture = Validators.date("31/12/2099")
        .isFutureDate("dd/MM/yyyy")
        .validate();

4) Combine format + temporal rule

boolean valid = Validators.date("31/12/2099")
        .hasDateFormat("dd/MM/yyyy")
        .isFutureDate("dd/MM/yyyy")
        .validate();

Map-based validation (object/payload)

Use Validator when you validate a payload with several fields.

import com.checkmate.Validator;
import com.checkmate.core.ValidationResult;
import com.checkmate.rules.EmailRule;
import com.checkmate.rules.PasswordRule;
import com.checkmate.rules.PhoneRule;
import com.checkmate.rules.common.NotEmptyRule;

Validator validator = new Validator()
        .addRule("email", new NotEmptyRule())
        .addRule("email", new EmailRule())
        .addRule("phone", new NotEmptyRule())
        .addRule("phone", new PhoneRule())
        .addRule("password", new NotEmptyRule())
        .addRule("password", new PasswordRule());

ValidationResult result = validator.validate(java.util.Map.of(
        "email", "wrong-email",
        "phone", "123",
        "password", "weak"
));

System.out.println(result.isValid()); // false
System.out.println(result.getFieldErrors());
System.out.println(result.getErrorsForField("email"));
System.out.println(result.getAllErrors());

Custom rules

Any class that implements com.checkmate.core.Rule can be used in both APIs.

import com.checkmate.core.Rule;

Rule noAdminEmail = value -> {
    if (value == null) {
        return java.util.Optional.of("email is required");
    }
    return value.endsWith("@admin.local")
            ? java.util.Optional.of("admin.local emails are not allowed")
            : java.util.Optional.empty();
};

boolean valid = Validators.email("root@admin.local")
        .withRule(noAdminEmail)
        .validate();

Main packages

• src/main/java/com/checkmate/core - base validator infrastructure
• src/main/java/com/checkmate/validators - fluent and specialized validators
• src/main/java/com/checkmate/rules/common - generic reusable rules
• src/main/java/com/checkmate/rules/email - email-specific rules
• src/main/java/com/checkmate/rules/password - password-specific rules
• src/main/java/com/checkmate/rules/date - date format/past/future rules
• src/test/java/com/checkmate - usage-oriented tests

Run tests

mvn test

License

MIT License. See LICENSE.