This guide will walk you through creating your first validator, using predefined rules, and handling validation errors. By the end, you’ll have a working validator for a user registration form.
Your First Validator Let’s start by creating a simple validator that checks if a string is not null and equals “xxx”.
Create a basic validator
Create a new validator instance and add custom rules using lambda expressions: import io.github.ApamateSoft.validator.Validator; public class HelloValidator { public static void main ( String [] args ) { // Instantiating a new validator Validator validator = new Validator. Builder (); // First rule: checks if string is not null validator . rule ( "Enter a text other than null" , ( String evaluate) -> { return evaluate != null ; }); // Second rule: checks if string equals "xxx" validator . rule ( "The text is different from 'xxx'" , ( String evaluate) -> { return evaluate . equals ( "xxx" ); }); // Test the validator System . out . println ( validator . isValid ( "xxx" )); // true System . out . println ( validator . isValid ( "abc" )); // false } }
Rules are evaluated in the order they were added
When a rule fails, the remaining rules are ignored
A string is valid only if it passes all rules
Use the Builder pattern
Simplify your code with the fluent Builder API: import io.github.ApamateSoft.validator.Validator; import java.util.Objects; public class HelloValidator { Validator validator = new Validator. Builder () . rule ( "Enter a text other than null" , Objects :: nonNull) . rule ( "The text is different from 'xxx'" , evaluate -> evaluate . equals ( "xxx" )) . build (); }
The Builder pattern provides a cleaner, more readable syntax for chaining rules. Using Predefined Rules Validator comes with 27+ predefined rules for common validation scenarios. Let’s explore some of the most useful ones.
Email Validation import io.github.ApamateSoft.validator.Validator; Validator emailValidator = new Validator. Builder () . required () . email () . maxLength ( 255 ) . build (); // Test it emailValidator . isValid ( "[email protected] " ); // true emailValidator . isValid ( "invalid-email" ); // false emailValidator . isValid ( "" ); // false
Number Validation import io.github.ApamateSoft.validator.Validator; Validator ageValidator = new Validator. Builder () . required () . onlyNumbers () . minValue ( 18 ) . maxValue ( 120 ) . build (); // Test it ageValidator . isValid ( "25" ); // true ageValidator . isValid ( "17" ); // false (too young) ageValidator . isValid ( "abc" ); // false (not a number)
Phone Number Pattern import io.github.ApamateSoft.validator.Validator; Validator phoneValidator = new Validator. Builder () . required () . numberPattern ( "(xxxx) xxx-xxxx" ) . build (); // Test it phoneValidator . isValid ( "(1234) 567-8901" ); // true phoneValidator . isValid ( "123-456-7890" ); // false (wrong format)
The x character in numberPattern is a placeholder for digits. Any other characters must match exactly.
Password Strength import io.github.ApamateSoft.validator.Validator; import static io.github.ApamateSoft.validator.utils.Alphabets. * ; Validator passwordValidator = new Validator. Builder () . required () . minLength ( 8 ) . mustContainMin ( 1 , ALPHA_LOWERCASE) . mustContainMin ( 1 , ALPHA_UPPERCASE) . mustContainMin ( 1 , NUMBER) . mustContainMin ( 1 , "@#$%^&*" ) . build (); // Test it passwordValidator . isValid ( "Password123!" ); // true passwordValidator . isValid ( "password" ); // false (no uppercase, no number) passwordValidator . isValid ( "Pass1!" ); // false (too short)
Handling Validation Errors Validator provides two approaches for handling validation errors: event-based and exception-based.
Event-Based Error Handling Use onInvalidEvaluation to register a callback that receives error messages:
import io.github.ApamateSoft.validator.Validator; Validator validator = new Validator. Builder () . required () . email () . build (); // Register error handler validator . onInvalidEvaluation (message -> { System . out . println ( "Validation failed: " + message); }); // Validate if ( ! validator . isValid ( "invalid-email" )) { // Error handler was called with the message }
Exception-Based Error Handling Use validOrFail to throw an exception when validation fails:
import io.github.ApamateSoft.validator.Validator; import io.github.ApamateSoft.validator.exceptions.InvalidEvaluationException; Validator validator = new Validator. Builder () . required () . email () . build (); try { validator . validOrFail ( "email" , "invalid-email" ); // Validation passed, continue processing } catch ( InvalidEvaluationException e ) { System . out . println ( "Field: " + e . getKey ()); // "email" System . out . println ( "Value: " + e . getValue ()); // "invalid-email" System . out . println ( "Error: " + e . getMessage ()); // "Email invalid" }
Comparing Strings For password confirmation or matching fields, use isMatch or compareOrFail:
import io.github.ApamateSoft.validator.Validator; Validator passwordValidator = new Validator. Builder () . required () . minLength ( 8 ) . setNotMatchMessage ( "Passwords do not match" ) . build (); // Event-based if ( passwordValidator . isMatch ( "password123" , "password123" )) { System . out . println ( "Passwords match!" ); } // Exception-based try { passwordValidator . compareOrFail ( "password" , "password123" , "password123" ); // Passwords match } catch ( InvalidEvaluationException e ) { System . out . println ( "Error: " + e . getMessage ()); }
Complete Example: User Registration Here’s a complete example that validates a user registration form:
import io.github.ApamateSoft.validator.Validator; import io.github.ApamateSoft.validator.exceptions.InvalidEvaluationException; import static io.github.ApamateSoft.validator.utils.Alphabets. * ; public class UserRegistration { // Define reusable validators private static final Validator emailValidator = new Validator. Builder () . required () . email () . maxLength ( 255 ) . build (); private static final Validator usernameValidator = new Validator. Builder () . required () . minLength ( 3 ) . maxLength ( 20 ) . onlyAlphanumeric () . build (); private static final Validator passwordValidator = new Validator. Builder () . required () . minLength ( 8 ) . mustContainMin ( 1 , ALPHA_LOWERCASE) . mustContainMin ( 1 , ALPHA_UPPERCASE) . mustContainMin ( 1 , NUMBER) . mustContainMin ( 1 , "@#$%^&*" ) . build (); public static void registerUser ( String email , String username , String password , String confirmPassword ) { try { // Validate each field emailValidator . validOrFail ( "email" , email); usernameValidator . validOrFail ( "username" , username); passwordValidator . validOrFail ( "password" , password); passwordValidator . compareOrFail ( "password" , password, confirmPassword); // All validations passed - proceed with registration System . out . println ( "Registration successful!" ); System . out . println ( "Email: " + email); System . out . println ( "Username: " + username); } catch ( InvalidEvaluationException e ) { // Handle validation error System . err . println ( "Validation failed for " + e . getKey () + ": " + e . getMessage ()); } } public static void main ( String [] args ) { // Test with valid data registerUser ( "[email protected] " , "johndoe" , "SecurePass123!" , "SecurePass123!" ); System . out . println (); // Test with invalid data registerUser ( "invalid-email" , "ab" , "weak" , "weak" ); } }
Output: Registration successful! Email: [email protected] Username: johndoe Validation failed for email: Email invalid
Next Steps Now that you understand the basics, explore these topics:
Core Concepts Learn about different validation approaches and patterns
Validation Rules Explore all 27+ predefined validation rules
Annotations Use annotations for declarative validation
Form Validation Build complete form validation systems