随机产生字母a--z, A-Z 的任意组合

VERSION 1.0    引自： http://www.coderanch.com/t/134491/Security/generating-secure-tokens

package demo;

import java.util.Random;

  

/*

 * This code is a discussion of an opinion in a technical forum.

 * You may develope ideas from this code. You may not use it directly.

 */

  

public class DM

{

    String getRandomIdentifier(int length) throws Exception

    {

        final int limitingValue = 64;// Whatever you decide, not me.

        if(length < limitingValue)

        {

            try

            {

                // The first step is to get a filename generator

                char lowerBound =   'a';

                char upperBound =   'z';

                Random randomCharacterGenerator = new Random();

                // Then get some characters

                char[] identifierBuffer = new char[length];//

                int index = identifierBuffer.length;//

                final int numericLowerBound = (int) lowerBound;

                final int numericUpperBound = (int) upperBound;

                final int range = numericUpperBound - numericLowerBound;//

                do

                {

                    // recoded in mesage edit, original defective

                    int getOne = randomCharacterGenerator.nextInt(range);

                    int next = numericLowerBound + getOne;

                    identifierBuffer[--index] = (char) next;

                }

                while(index > 0x00000000);

                return new String(identifierBuffer);//

            }

            catch(ArrayIndexOutOfBoundsException aioobe)

            {

                System.out.println(aioobe.getMessage());

            }

        }

        else

        {

            throw new Exception("Contact system administrator.");//

        }

        return null;

    }

}

VERSION 2.0    改进型：

package token;

import java.util.Random;

public class DM {
    public static void main(String[] args) throws Exception {
        System.out.println("1==97===:" + (int) 'a');
        System.out.println("2==122===:" + (int) 'z');
        System.out.println("3==65===:" + (int) 'A');
        System.out.println("4===90==:" + (int) 'Z');
        DM mn = new DM();
        System.out.println(mn.getRandomIdentifier(26));
    }

    String getRandomIdentifier(int length) throws Exception {
        final int limitingValue = 164;// Whatever you decide, not me.
        if (length < limitingValue) {
            try {
                // 26个小写+26个大小 = 52 字母
                final int range = 52;//
                char[] charStr = new char[range];
                int j = 0;
                // A=65, z =122
                for (int i = 65; i <= 122; i++) {
                    // Z--a 之间的跳过
                    if (i > 90 && i < 97) {
                        continue;
                    }
                    charStr[j] = (char) i;   // 这里将保存52个大小字母
                    j++;
                }

                   // 这里其实可以将 0 - 9 的数字也添加进去
                Random randomCharacterGenerator = new Random();
                // Then get some characters
                char[] identifierBuffer = new char[length];//
                int index = identifierBuffer.length;//
                do {
                    // 产生0至51 共52个随机数，用于索引字母数组
                    int getOne = randomCharacterGenerator.nextInt(range);
                    identifierBuffer[--index] = charStr[getOne];
                } while (index > 0x00000000);
                return new String(identifierBuffer);//
            } catch (ArrayIndexOutOfBoundsException aioobe) {
                System.out.println(aioobe.getMessage());
            }
        } else {
            throw new Exception("Contact system administrator.");//
        }
        return null;
    }

}