Secure Token Generator

App.java

package net.jeffreypratt.edu.security;

public class App {
    public static void main(String[] args) {
        var count = 1;
        
        if (args.length > 0) {
            count = Integer.parseInt(args[0]);
        }

        try {
            var provider = new SecureTokenProvider(TokenAlphabet.FULL, 20);

            provider.stream()
                .limit(count)
                .forEach(System.out::println);

        } catch (CouldNotCreateProviderException e) {
            System.out.println(e.getMessage());
            System.exit(1);
        }
    }
}

CouldNotCreateProviderException.java

package net.jeffreypratt.edu.security;

public class CouldNotCreateProviderException extends Exception {
    public CouldNotCreateProviderException(Throwable t) {
        super(String.format("Could not create provider: %s", t.getMessage()), t);
    }
}

SecureTokenGenerator.java

package net.jeffreypratt.edu.security;

import java.security.SecureRandom;
import java.security.NoSuchAlgorithmException;
import java.util.stream.Stream;

public class SecureTokenProvider {
    private final String alphabet;
    private final SecureRandom random;
    private final int length;

    private static final int DEFAULT_LENGTH = 16;

    private static final String DEFAULT_ALPHABET = TokenAlphabet.ASCII_LETTERS;

    public SecureTokenProvider() throws CouldNotCreateProviderException {
        this(DEFAULT_ALPHABET);
    }

    public SecureTokenProvider(String alphabet) throws CouldNotCreateProviderException {
        this(alphabet, DEFAULT_LENGTH);
    }

    public SecureTokenProvider(int length) throws CouldNotCreateProviderException {
        this(DEFAULT_ALPHABET, length);
    }

    public SecureTokenProvider(String alphabet, int length) throws CouldNotCreateProviderException {
        try {
            this.alphabet = alphabet;
            this.length = length;
            this.random = SecureRandom.getInstanceStrong();
        } catch (NoSuchAlgorithmException e) {
            throw new CouldNotCreateProviderException(e);
        }
    }

    SecureTokenProvider(String alphabet, SecureRandom random, int length) {
        this.alphabet = alphabet;
        this.random = random;
        this.length = length;
    }

    public String nextToken(int length) {
        var builder = new StringBuilder(length);

        for (int i = 0; i < length; i++) {
            int index = random.nextInt(alphabet.length());
            builder.append(alphabet.charAt(index));
        }

        return builder.toString();
    }

    public Stream<String> stream() {
        return Stream.generate(() -> nextToken(length));
    }
}

TokenAlphabet.java

package net.jeffreypratt.edu.security;

public class TokenAlphabet {
    public static final String ASCII_LOWERCASE = "abcdefghijklmnopqrstuvwxyz";
    public static final String ASCII_UPPERCASE = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    public static final String ASCII_LETTERS = ASCII_UPPERCASE + ASCII_LOWERCASE;
    public static final String DIGITS = "0123456789";
    public static final String SYMBOLS = "`~!@#$%^&*()_+-={}|[]\\:\";',./<>?";
    public static final String FULL = ASCII_UPPERCASE + ASCII_LOWERCASE + DIGITS + SYMBOLS;
}