Skip to main content

​
What is Validator?

Validator is a Java library that simplifies string validation by allowing you to chain a series of rules. Whether you’re validating user input, form data, or API parameters, Validator provides an intuitive and flexible API to ensure your strings meet specific criteria.

Key Features

  • Chainable Rules: Build complex validation logic by chaining multiple rules together
  • Predefined Validators: 27+ built-in validators for common use cases (email, URL, phone patterns, etc.)
  • Custom Rules: Define your own validation logic with lambda expressions
  • Annotation Support: Use annotations to validate POJOs declaratively
  • Flexible Error Handling: Choose between events or exceptions for validation failures
  • Internationalization: Built-in support for English and Spanish error messages

​
Why Use Validator?

Validation is a critical part of any application, but it often leads to verbose, repetitive code. Validator solves this problem by providing:

​
Clean, Readable Code

Instead of scattered if-statements and null checks, Validator lets you express validation rules declaratively: 
Validator emailValidator = new Validator.Builder()
    .required()
    .email()
    .maxLength(255)
    .build();

​
Reusability

Define validators once and reuse them throughout your application: 
public class Validators {
    public static final Validator PASSWORD = new Validator.Builder()
        .required()
        .minLength(8)
        .mustContainMin(1, "ABCDEFGHIJKLMNOPQRSTUVWXYZ")
        .mustContainMin(1, "0123456789")
        .build();
}

​
Type Safety

Validator works with Java’s type system and provides compile-time safety through its fluent API.

​
Validation Approaches

Validator supports three different approaches to validation:

Builder Pattern

Chain rules programmatically using the fluent Builder API

Annotations

Declare validation rules directly on class fields

Custom Rules

Define your own validation logic with lambda expressions

​
How It Works

Validator evaluates rules in the order they are defined. When validation fails:
1

Rule Evaluation

Each rule is checked sequentially against the string
2

First Failure

When a rule fails, evaluation stops immediately
3

Error Handling

The associated error message is returned via event callback or exception
Important: A string is considered valid only if it passes ALL rules. Validation stops at the first failure, making the process efficient.

​
Use Cases

Validator is perfect for:
  • Form Validation: Validate user registration, login, and profile forms
  • API Input: Ensure API request parameters meet requirements
  • Data Sanitization: Verify data before database operations
  • Configuration Validation: Check application settings and properties
  • Business Rules: Enforce domain-specific validation logic

​
Example: User Registration

Here’s a quick example of validating user registration data: 
import io.github.ApamateSoft.validator.Validator;
import io.github.ApamateSoft.validator.exceptions.InvalidEvaluationException;

public class UserRegistration {
    private Validator emailValidator = new Validator.Builder()
        .required()
        .email()
        .build();
    
    private Validator passwordValidator = new Validator.Builder()
        .required()
        .minLength(8)
        .mustContainOne("ABCDEFGHIJKLMNOPQRSTUVWXYZ")
        .mustContainOne("0123456789")
        .build();
    
    public void register(String email, String password) {
        try {
            emailValidator.validOrFail("email", email);
            passwordValidator.validOrFail("password", password);
            
            // Proceed with registration
            System.out.println("Registration successful!");
        } catch (InvalidEvaluationException e) {
            System.err.println(e.getKey() + ": " + e.getMessage());
        }
    }
}

​
Requirements

  • Java 11 or higher
  • No external dependencies (except for testing)

​
Next Steps

Installation

Add Validator to your project with Maven or Gradle

Quick Start

Build your first validator in 5 minutes

Build docs developers (and LLMs) love

Get started for freeTalk to us