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Utility classes developed at Adrian Smith Software (A.S.S.)
There is a newer version: 21.0.1
package com.databasesandlife.util.gwtsafe;

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonValue;
import com.google.gwt.user.client.rpc.IsSerializable;

import javax.annotation.Nonnull;
import java.io.Serializable;
import java.util.*;

import static java.util.Arrays.asList;

/**
 * Wraps a string containing a cleartext password.
 * The purpose of this class is to increase type-safety over using a plain string.
 *
 * @author This source is copyright Adrian Smith and licensed under the LGPL 3.
 * @see Project on GitHub
 */
@SuppressWarnings("NotNullFieldNotInitialized") // due to no-arg constructor required for serialization
public class CleartextPassword implements Serializable, IsSerializable {

    protected @Nonnull String cleartext;

    @JsonCreator
    public CleartextPassword(@Nonnull String c) {
        cleartext = c;
    }

    @JsonValue
    public @Nonnull String getCleartext() { return cleartext; }
    
    /** @deprecated Do not use, required for GWT */
    @Deprecated private CleartextPassword() { }

    /**
     * Generates a random password.
     * A-Z, a-z, 0-9 characters are used, with the exception confusing characters such as uppercase O and digit 0 are not used.
     * The objective is that:
     * 

     *     the passwords can be written down (thus confusing characters are removed)
     *     and also that the password can be used in situations where special encoding is needed for example GET requests
     *          (thus there are no special characters.)
     * 
     * Make up for "lack of randomness" by making the password longer.
     */
    public static @Nonnull CleartextPassword newRandom(int length) {
        var chars = new ArrayList<>();

        for (var c = 'A'; c <= 'Z'; c++) chars.add(c);
        for (var c = 'a'; c <= 'z'; c++) chars.add(c);
        for (var c = '0'; c <= '9'; c++) chars.add(c);

        chars.removeAll(asList('O', '0'));
        chars.removeAll(asList('I', 'l', '1'));
        chars.removeAll(asList('S', '5'));
        chars.removeAll(asList('2', 'Z'));

        var random = new Random();
        var result = new StringBuilder(length);
        for (var i = 0; i < length; i++) {
            var charIdx = random.nextInt(chars.size());
            result.append(chars.get(charIdx));
        }

        return new CleartextPassword(result.toString());
    }

    /** Generates a new password of a reasonable length; see {@link #newRandom(int)} */
    public static @Nonnull CleartextPassword newRandom() {
        return newRandom(15);
    }

    @Override
    public boolean equals(Object o) {
        if (o == null || !getClass().equals(o.getClass())) return false;

        var that = (CleartextPassword) o;
        return cleartext.equals(that.cleartext);
    }

    @Override
    public int hashCode() {
        return 3458 + cleartext.hashCode();
    }

    @Override
    public String toString() {
        return getClass().getSimpleName()+"("+cleartext+")";
    }
}