How to hash some String with SHA-256 in Java?

java

hashing

sha-256

encoding

byAnton Shumikhin·Aug 22, 2024

Here's your express ride to SHA-256 hashing in Java using MessageDigest:

import java.security.MessageDigest;
import java.nio.charset.StandardCharsets;

public class Main {
    public static void main(String[] args) throws Exception {
        String theSecret = "OpenSesame";
        MessageDigest theDigest = MessageDigest.getInstance("SHA-256");
        byte[] hashedBytes = theDigest.digest(theSecret.getBytes(StandardCharsets.UTF_8));
        System.out.println(bytesToHex(hashedBytes)); // The Hex string we long for!
    }

    // Hex conversion better than grandma's apple pie recipe!
    private static String bytesToHex(byte[] hash) {
        StringBuilder hexString = new StringBuilder(2 * hash.length);
        for (int i = 0; i < hash.length; i++) {
            String hex = Integer.toHexString(0xff & hash[i]);
            if(hex.length() == 1) {
                hexString.append('0'); // Because zeros have feelings too!
            }
            hexString.append(hex);
        }
        return hexString.toString();
    }
}

The function bytesToHex is your best friend for converting hashed bytes to a hex String.

Correct encoding and exception handling cannot be overemphasized. Use StandardCharsets.UTF_8 for consistency across platforms. Get cosy with NoSuchAlgorithmException for a rock-solid code!

Covering the bases

Choosing the encoding ref

Handling binary data like a champ means safely translating it to a hex string or base64 string. All hail safe representation of binary without corruption!

Library Magic

Apache Commons Codec or Google's Guava libraries can make your life easier than a Sunday morning. Here's how with Apache Commons Codec:

import org.apache.commons.codec.digest.DigestUtils;

public class HashingExample {
    // One-liner hasher, because why not?
    public static String sha256hex(String input) {
        return DigestUtils.sha256Hex(input);
    }
}

And the charming Guava way:

import com.google.common.hash.Hashing;

public class HashingExample {
    // Hashing so easy, even your cat can do it!
    public static String sha256hex(String input) {
        return Hashing.sha256().hashString(input, StandardCharsets.UTF_8).toString();
    }
}

Exception handling

Play good defense with NoSuchAlgorithmException by logging or firing a custom exception. UnsupportedEncodingException is another dragon to slay when swinging from String to bytes.

Pro tips for hashing heroes

String conversion and Unicode wonders

Direct conversion from hash bytes to a String is as good an idea as pineapple on pizza! Always use encoding — Base64.getEncoder().encodeToString() or your custom-made hex method.