Java Random Alphanumeric String

Generating Random Alphanumeric Strings in Java

Java offers several ways to create random alphanumeric strings. For Spring Boot apps, consider security implications; use java.security.SecureRandom for cryptographically secure strings (e.g., for tokens).

Method 1: Using SecureRandom (Recommended)

import java.security.SecureRandom;

public static String generateRandomAlphanumericString(int length) {
    String chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
    SecureRandom random = new SecureRandom();
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < length; i++) {
        sb.append(chars.charAt(random.nextInt(chars.length())));
    }
    return sb.toString();
}

Method 2: Using Random (Less Secure)

While simpler, java.util.Random is less secure for sensitive applications.

import java.util.Random;

public static String generateRandomAlphanumericStringUnsafe(int length) {
    String chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
    Random random = new Random();
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < length; i++) {
        sb.append(chars.charAt(random.nextInt(chars.length())));
    }
    return sb.toString();
}

Usage:

String secureString = generateRandomAlphanumericString(10); // Secure, 10 characters
String unsafeString = generateRandomAlphanumericStringUnsafe(5); // Insecure, 5 characters

Remember: SecureRandom is crucial for security-sensitive contexts like session IDs or tokens. Choose the appropriate method based on your application's needs. Adjust length to control string length.