DefaultRandomStringGenerator.java

/*
 * Licensed to Jasig under one or more contributor license
 * agreements. See the NOTICE file distributed with this work
 * for additional information regarding copyright ownership.
 * Jasig licenses this file to you under the Apache License,
 * Version 2.0 (the "License"); you may not use this file
 * except in compliance with the License.  You may obtain a
 * copy of the License at the following location:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.jasig.cas.util;

import java.security.SecureRandom;

/**
 * Implementation of the RandomStringGenerator that allows you to define the
 * length of the random part.
 *
 * @author Scott Battaglia

 * @since 3.0
 */
public final class DefaultRandomStringGenerator implements
    RandomStringGenerator {

    /** The array of printable characters to be used in our random string. */
    private static final char[] PRINTABLE_CHARACTERS = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ012345679"
        .toCharArray();

    /** The default maximum length. */
    private static final int DEFAULT_MAX_RANDOM_LENGTH = 35;

    /** An instance of secure random to ensure randomness is secure. */
    private SecureRandom randomizer = new SecureRandom();

    /** The maximum length the random string can be. */
    private final int maximumRandomLength;

    public DefaultRandomStringGenerator() {
        this.maximumRandomLength = DEFAULT_MAX_RANDOM_LENGTH;
    }

    public DefaultRandomStringGenerator(final int maxRandomLength) {
        this.maximumRandomLength = maxRandomLength;
    }

    public int getMinLength() {
        return this.maximumRandomLength;
    }

    public int getMaxLength() {
        return this.maximumRandomLength;
    }

    public String getNewString() {
        final byte[] random = getNewStringAsBytes();

        return convertBytesToString(random);
    }


    public byte[] getNewStringAsBytes() {
        final byte[] random = new byte[this.maximumRandomLength];

        this.randomizer.nextBytes(random);

        return random;
    }

    private String convertBytesToString(final byte[] random) {
        final char[] output = new char[random.length];
        for (int i = 0; i < random.length; i++) {
            final int index = Math.abs(random[i] % PRINTABLE_CHARACTERS.length);
            output[i] = PRINTABLE_CHARACTERS[index];
        }

        return new String(output);
    }
}