Tomcat example source code file (UUIDGenerator.java)

This example Tomcat source code file (UUIDGenerator.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Tomcat tags/keywords

arrayindexoutofboundsexception, bits_per_byte, bytes_per_int, bytes_per_int, random, random, securerandom, securerandom, security, unable, util, uuid_length, uuid_version, uuid_version, uuidgenerator

The Tomcat UUIDGenerator.java source code

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF 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
 * 
 *      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.apache.catalina.tribes.util;

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

/**
 * simple generation of a UUID 
 * @author Filip Hanik
 * @version 1.0
 */
public class UUIDGenerator {
    public static final int UUID_LENGTH = 16;
    public static final int UUID_VERSION = 4;
    public static final int BYTES_PER_INT = 4;
    public static final int BITS_PER_BYTE = 8;
    
    protected static SecureRandom secrand = null;
    protected static Random rand = new Random(System.currentTimeMillis());
    static {
        secrand = new SecureRandom();
        secrand.setSeed(rand.nextLong());
    }
    
    public static byte[] randomUUID(boolean secure) {
        byte[] result = new byte[UUID_LENGTH];
        return randomUUID(secure,result,0);
    }

    public static byte[] randomUUID(boolean secure, byte[] into, int offset) {
        if ( (offset+UUID_LENGTH)>into.length )
            throw new ArrayIndexOutOfBoundsException("Unable to fit "+UUID_LENGTH+" bytes into the array. length:"+into.length+" required length:"+(offset+UUID_LENGTH));
        Random r = (secure&&(secrand!=null))?secrand:rand;
        nextBytes(into,offset,UUID_LENGTH,r);
        into[6+offset] &= 0x0F;
        into[6+offset] |= (UUID_VERSION << 4);
        into[8+offset] &= 0x3F; //0011 1111
        into[8+offset] |= 0x80; //1000 0000
        return into;
    }
    
    /**
     * Same as java.util.Random.nextBytes except this one we dont have to allocate a new byte array
     * @param into byte[]
     * @param offset int
     * @param length int
     * @param r Random
     */
    public static void nextBytes(byte[] into, int offset, int length, Random r) {
        int numRequested = length;
        int numGot = 0, rnd = 0;
        while (true) {
            for (int i = 0; i < BYTES_PER_INT; i++) {
                if (numGot == numRequested) return;
                rnd = (i == 0 ? r.nextInt() : rnd >> BITS_PER_BYTE);
                into[offset+numGot] = (byte) rnd;
                numGot++;
            }
        }
    }

}