Email validation using Java Regex

📧 Email Validation Using Java Regular Expressions (Regex)

Topic: Java Regex Pattern for Email Validation

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🧩 Overview

In this post, we’ll explore how to validate email addresses in Java using Regular Expressions (Regex).
The regex pattern enforces strict rules for valid email structures — ensuring only properly formatted email IDs are accepted.

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🧠 Regex Pattern

^[A-Z0-9._]+@[A-Z0-9-]+\.[A-Z]{2,6}$

🔍 Pattern Breakdown

Symbol	Meaning	Description
^	Start of the pattern	Ensures the match begins from the start of the string
[A-Z0-9._]+	First part	The local part (before @) must contain uppercase letters (A-Z), digits (0-9), and . or _
@	Separator	Separates the username and domain parts
[A-Z0-9-]+	Second part	The domain name (after @) must contain letters, digits, or hyphens (-)
\.[A-Z]{2,6}	Third part	The domain extension must begin with a . followed by 2 to 6 letters (A-Z)
$	End of the pattern	Ensures the match ends at the end of the string

🧩 In simple terms:

The email must look like USERNAME@DOMAIN.TLD,
where:

• Username = letters, numbers, dots, or underscores

• Domain = letters or numbers

• TLD (Top-Level Domain) = 2–6 letters only (e.g., .com, .org, .co.in)

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🧰 Java Implementation

Here’s the complete Java example to validate emails using this regex pattern.

package com.vinod.test;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * @author vinod.kumaran
 *
 * Simple email validator using Java Regular Expressions.
 *
 * Pattern: ^[A-Z0-9._]+@[A-Z0-9-]+\.[A-Z]{2,6}$
 *
 * ^ = Start of pattern
 * [A-Z0-9._] = First part: allowed characters before '@'
 * @[A-Z0-9-] = Second part: allowed characters after '@'
 * \.[A-Z]{2,6} = Third part: domain extension with 2–6 letters
 * $ = End of pattern
 */
public class EmailValidator {

    // Compile the regex pattern (case-insensitive)
    public static final Pattern EMAIL_REGEX =
            Pattern.compile("^[A-Z0-9._]+@[A-Z0-9-]+\\.[A-Z]{2,6}$",
                    Pattern.CASE_INSENSITIVE);

    public static void main(String[] args) {
        // Valid email
        System.out.println(validate("kkvinod@pretechsol.com"));

        // Invalid email: first part contains '%'
        System.out.println(validate("kkvin%od@pretechsol.com"));

        // Invalid email: second part contains '_'
        System.out.println(validate("kkvinod@prete_chsol.com"));

        // Invalid email: domain extension > 6 characters
        System.out.println(validate("kkvinod@pretechsol.comcomcom"));
    }

    // Validation method
    public static boolean validate(String emailAddress) {
        Matcher matcher = EMAIL_REGEX.matcher(emailAddress);
        return matcher.find();
    }
}

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🧪 Sample Output

true
false
false
false

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✅ Explanation of Results

Email	Expected Result	Reason
kkvinod@pretechsol.com	✅ true	Valid format
kkvin%od@pretechsol.com	❌ false	% not allowed before @
kkvinod@prete_chsol.com	❌ false	_ not allowed in domain name
kkvinod@pretechsol.comcomcom	❌ false	TLD (extension) exceeds 6 letters