史上最全的java随机数生成算法[转载]

 package com.zuidaima.core.util;

 import java.util.Random;

 public class RandomUtil {
     public static final String ALLCHAR = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
     public static final String LETTERCHAR = "abcdefghijkllmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
     public static final String NUMBERCHAR = "0123456789";

     /**
      * 返回一个定长的随机字符串(只包含大小写字母、数字)
      *
      * @param length
      *            随机字符串长度
      * @return 随机字符串
      */
     public static String generateString(int length) {
         StringBuffer sb = new StringBuffer();
         Random random = new Random();
         for (int i = 0; i < length; i++) {
             sb.append(ALLCHAR.charAt(random.nextInt(ALLCHAR.length())));
         }
         return sb.toString();
     }

     /**
      * 返回一个定长的随机纯字母字符串(只包含大小写字母)
      *
      * @param length
      *            随机字符串长度
      * @return 随机字符串
      */
     public static String generateMixString(int length) {
         StringBuffer sb = new StringBuffer();
         Random random = new Random();
         for (int i = 0; i < length; i++) {
             sb.append(ALLCHAR.charAt(random.nextInt(LETTERCHAR.length())));
         }
         return sb.toString();
     }

     /**
      * 返回一个定长的随机纯大写字母字符串(只包含大小写字母)
      *
      * @param length
      *            随机字符串长度
      * @return 随机字符串
      */
     public static String generateLowerString(int length) {
         return generateMixString(length).toLowerCase();
     }

     /**
      * 返回一个定长的随机纯小写字母字符串(只包含大小写字母)
      *
      * @param length
      *            随机字符串长度
      * @return 随机字符串
      */
     public static String generateUpperString(int length) {
         return generateMixString(length).toUpperCase();
     }

     /**
      * 生成一个定长的纯0字符串
      *
      * @param length
      *            字符串长度
      * @return 纯0字符串
      */
     public static String generateZeroString(int length) {
         StringBuffer sb = new StringBuffer();
         for (int i = 0; i < length; i++) {
             sb.append('0');
         }
         return sb.toString();
     }

     /**
      * 根据数字生成一个定长的字符串，长度不够前面补0
      *
      * @param num
      *            数字
      * @param fixdlenth
      *            字符串长度
      * @return 定长的字符串
      */
     public static String toFixdLengthString(long num, int fixdlenth) {
         StringBuffer sb = new StringBuffer();
         String strNum = String.valueOf(num);
         if (fixdlenth - strNum.length() >= 0) {
             sb.append(generateZeroString(fixdlenth - strNum.length()));
         } else {
             throw new RuntimeException("将数字" + num + "转化为长度为" + fixdlenth
                     + "的字符串发生异常！");
         }
         sb.append(strNum);
         return sb.toString();
     }

     /**
      * 每次生成的len位数都不相同
      *
      * @param param
      * @return 定长的数字
      */
     public static int getNotSimple(int[] param, int len) {
         Random rand = new Random();
         for (int i = param.length; i > 1; i--) {
             int index = rand.nextInt(i);
             int tmp = param[index];
             param[index] = param[i - 1];
             param[i - 1] = tmp;
         }
         int result = 0;
         for (int i = 0; i < len; i++) {
             result = result * 10 + param[i];
         }
         return result;
     }

     public static void main(String[] args) {
         System.out.println("返回一个定长的随机字符串(只包含大小写字母、数字):" + generateString(10));
         System.out
                 .println("返回一个定长的随机纯字母字符串(只包含大小写字母):" + generateMixString(10));
         System.out.println("返回一个定长的随机纯大写字母字符串(只包含大小写字母):"
                 + generateLowerString(10));
         System.out.println("返回一个定长的随机纯小写字母字符串(只包含大小写字母):"
                 + generateUpperString(10));
         System.out.println("生成一个定长的纯0字符串:" + generateZeroString(10));
         System.out.println("根据数字生成一个定长的字符串，长度不够前面补0:"
                 + toFixdLengthString(123, 10));
         int[] in = { 1, 2, 3, 4, 5, 6, 7 };
         System.out.println("每次生成的len位数都不相同:" + getNotSimple(in, 3));
     }
 }