How to Hash a String Using SHA-256 in Java?

Question

How can I hash a String using SHA-256 in Java?

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class HashExample {
    public static void main(String[] args) {
        String input = "Hello, World!";
        String hashedOutput = hashString(input);
        System.out.println("Hashed Output: " + hashedOutput);
    }

    public static String hashString(String input) {
        try {
            MessageDigest digest = MessageDigest.getInstance("SHA-256");
            byte[] hash = digest.digest(input.getBytes());
            return bytesToHex(hash);
        } catch (NoSuchAlgorithmException e) {
            throw new RuntimeException(e);
        }
    }

    private static String bytesToHex(byte[] hash) {
        StringBuilder hexString = new StringBuilder();
        for (byte b : hash) {
            String hex = Integer.toHexString(0xff & b);
            if (hex.length() == 1) hexString.append('0');
            hexString.append(hex);
        }
        return hexString.toString();
    }
}

Answer

Hashing a string using SHA-256 in Java is straightforward with the built-in `MessageDigest` class. SHA-256 is a widely adopted hashing algorithm that produces a fixed-size (256-bit) hash value, primarily used for data integrity and password storage.

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class HashExample {
    public static void main(String[] args) {
        String input = "Hello, World!";
        String hashedOutput = hashString(input);
        System.out.println("Hashed Output: " + hashedOutput);
    }

    public static String hashString(String input) {
        try {
            MessageDigest digest = MessageDigest.getInstance("SHA-256");
            byte[] hash = digest.digest(input.getBytes());
            return bytesToHex(hash);
        } catch (NoSuchAlgorithmException e) {
            throw new RuntimeException(e);
        }
    }

    private static String bytesToHex(byte[] hash) {
        StringBuilder hexString = new StringBuilder();
        for (byte b : hash) {
            String hex = Integer.toHexString(0xff & b);
            if (hex.length() == 1) hexString.append('0');
            hexString.append(hex);
        }
        return hexString.toString();
    }
}

Causes

Choosing the correct hashing algorithm: Ensure that SHA-256 is suitable for your use case as other algorithms may be more efficient.
Handling exceptions properly: Not managing exceptions can lead to runtime errors.

Solutions

Import the necessary `java.security.MessageDigest` class when implementing SHA-256 hashing.
Use the right encoding to convert the input string to bytes, typically UTF-8.
Implement a utility method to convert the resultant byte array to a hexadecimal string format for readability.

Common Mistakes

Mistake: Not using the correct character encoding when converting strings to bytes.

Solution: Always specify UTF-8 encoding to handle characters appropriately.

Mistake: Forgetting to handle exceptions may crash the application.

Solution: Wrap your code in try-catch blocks to manage `NoSuchAlgorithmException`.

Helpers

Java SHA-256
hash string in Java
SHA-256 example Java
Java security
string hashing Java