Here you can find the source of randomString(int length)
| Parameter | Description |
|---|---|
| length | the desired length of the random String to return. |
public static final String randomString(int length)
//package com.java2s; /**/*from w w w . j a v a 2s .c o m*/ * $RCSfile: StringUtils.java,v $ * $Revision: 1.11.2.3 $ * $Date: 2001/03/06 16:38:31 $ * * Copyright (C) 2000 CoolServlets.com. All rights reserved. * * =================================================================== * The Apache Software License, Version 1.1 * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in * the documentation and/or other materials provided with the * distribution. * * 3. The end-user documentation included with the redistribution, * if any, must include the following acknowledgment: * "This product includes software developed by * CoolServlets.com (http://www.Yasna.com)." * Alternately, this acknowledgment may appear in the software itself, * if and wherever such third-party acknowledgments normally appear. * * 4. The names "Jive" and "CoolServlets.com" must not be used to * endorse or promote products derived from this software without * prior written permission. For written permission, please * contact webmaster@Yasna.com. * * 5. Products derived from this software may not be called "Jive", * nor may "Jive" appear in their name, without prior written * permission of CoolServlets.com. * * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE * DISCLAIMED. IN NO EVENT SHALL COOLSERVLETS.COM OR * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. * ==================================================================== * * This software consists of voluntary contributions made by many * individuals on behalf of CoolServlets.com. For more information * on CoolServlets.com, please see <http://www.Yasna.com>. */ import java.util.*; public class Main { /** * Initialization lock for the whole class. Init's only happen once per * class load so this shouldn't be a bottleneck. */ private static Object initLock = new Object(); /** * Pseudo-random number generator object for use with randomString(). * The Random class is not considered to be cryptographically secure, so * only use these random Strings for low to medium security applications. */ private static Random randGen = null; /** * Array of numbers and letters of mixed case. Numbers appear in the list * twice so that there is a more equal chance that a number will be picked. * We can use the array to get a random number or letter by picking a random * array index. */ private static char[] numbersAndLetters = null; /** * Returns a random String of numbers and letters of the specified length. * The method uses the Random class that is built-in to Java which is * suitable for low to medium grade security uses. This means that the * output is only pseudo random, i.e., each number is mathematically * generated so is not truly random.<p> * * For every character in the returned String, there is an equal chance that * it will be a letter or number. If a letter, there is an equal chance * that it will be lower or upper case.<p> * * The specified length must be at least one. If not, the method will return * null. * * @param length the desired length of the random String to return. * @return a random String of numbers and letters of the specified length. */ public static final String randomString(int length) { if (length < 1) { return null; } //Init of pseudo random number generator. if (randGen == null) { synchronized (initLock) { if (randGen == null) { randGen = new Random(); //Also initialize the numbersAndLetters array numbersAndLetters = ("0123456789abcdefghijklmnopqrstuvwxyz" + "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ") .toCharArray(); } } } //Create a char buffer to put random letters and numbers in. char[] randBuffer = new char[length]; for (int i = 0; i < randBuffer.length; i++) { randBuffer[i] = numbersAndLetters[randGen.nextInt(71)]; } return new String(randBuffer); } }