com.sun.syndication.aqueduct.prevayler.uuid.UUIDGen.java Source code

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Here is the source code for com.sun.syndication.aqueduct.prevayler.uuid.UUIDGen.java

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/**
 * Copyright 2005 - Rome|Aqueduct Project Team
 * http://rome.dev.java.net/
 *
 * Licensed 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
 *
 *     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 com.sun.syndication.aqueduct.prevayler.uuid;

import java.security.SecureRandom;
import java.util.Random;

/**
 * UUIDGen is adapted from Apache's org.apache.commons.id.uuid package.
 *
 * @author Mark Woodman
 */
public class UUIDGen {
    /** SecureRandom (or Random as failover) used to generate UUID's */
    private static Random random;

    /** Used to build output as hex. Adapted from org.apache.commons.id.Hex */
    private static final char[] DIGITS = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd',
            'e', 'f' };

    /**
     * Constructor.  Initializes random generator, attempting
     * first to use SecureRandom, then failing over to Random.
     */
    public UUIDGen() {
        try {
            random = SecureRandom.getInstance("SHA1PRNG", "SUN");
        } catch (Exception e) {
            random = new Random();
        }
    }

    /**
     * Generates a string representation of a version four UUID.
     * @return
     */
    public String nextUUID() {
        return getUUIDString(getBytes());
    }

    /**
     * Generate byte array using random generator.
     * Code adapted from org.apache.commons.id.uuid.VersionFourGenerator.java
     * @return
     */
    private byte[] getBytes() {
        byte[] raw = new byte[16];
        random.nextBytes(raw);
        raw[6] &= 0x0F;
        raw[6] |= (4 << 4);
        raw[8] &= 0x3F; //0011 1111
        raw[8] |= 0x80; //1000 0000
        return raw;
    }

    /**
     * Turn a byte array into a version four UUID string.
     * Adapted from org.apache.commons.id.uuid.UUID.java
     * @param raw
     * @return
     */
    private String getUUIDString(byte[] raw) {
        StringBuffer buf = new StringBuffer(new String(encodeHex(raw)));
        while (buf.length() != 32) {
            buf.insert(0, "0");
        }
        buf.ensureCapacity(32);
        buf.insert(8, '-');
        buf.insert(13, '-');
        buf.insert(18, '-');
        buf.insert(23, '-');
        return buf.toString();
    }

    /**
     * Converts an array of bytes into an array of characters representing
     * the hexidecimal values of each byte in order. The returned array will
     * be double the length of the passed array, as it takes two characters
     * to represent any given byte.
     *
     * Adapted from org.apache.commons.id.Hex
     *
     * @param data   a byte[] to convert to Hex characters
     * @return A char[] containing hexidecimal characters
     */
    private static char[] encodeHex(byte[] data) {
        int l = data.length;
        char[] out = new char[l << 1];
        for (int i = 0, j = 0; i < l; i++) {
            out[j++] = DIGITS[(0xF0 & data[i]) >>> 4];
            out[j++] = DIGITS[0x0F & data[i]];
        }
        return out;
    }
}