java生成随机数

package com.rd.p2p.common.util;

import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.Random;
import java.util.Set;
import java.util.UUID;

/**
 * 工具类-随机数

 */
public class RandomUtil {

    /**
     * 获取从a至z，长度为length随机数
     * 
     * @return
     */
    public static String getRandomStr(int length) {
        String base = "abcdefghijklmnopqrstuvwxyz";
        Random random = new Random();
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < length; i++) {
            int number = random.nextInt(base.length());
            sb.append(base.charAt(number));
        }
        return sb.toString();
    }

    /**
     * 获取范围内int值
     * 
     * @param 获取范围内int值
     * @return
     */
    public static int getRandomRange(int max, int min) {
        return (int) (Math.random() * (max - min) + min);
    }

    /**
     * 获取随机长度随机字符
     * 
     * @param length base
     * @return
     */
    public static String getRandomString(int length, String base) { // length表示生成字符串的长度
        Random random = new Random();
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < length; i++) {
            int number = random.nextInt(base.length());
            sb.append(base.charAt(number));
        }
        return sb.toString();
    }

    /**
     * 获取随机长度随机字符
     * 
     * @param length
     * @return
     */
    public static String getRandomString(int length) { // length表示生成字符串的长度
        String base = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
        Random random = new Random();
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < length; i++) {
            int number = random.nextInt(base.length());
            sb.append(base.charAt(number));
        }
        return sb.toString();
    }

    /**
     * 获取随机长度随机数字
     * 
     * @param length
     * @return
     */
    public static String getRandomNumString(int length) { // length表示生成字符串的长度
        String base = "0123456789";
        Random random = new Random();
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < length; i++) {
            int number = random.nextInt(base.length());
            sb.append(base.charAt(number));
        }
        return sb.toString();
    }

    /**
     * 返回随机数组
     * 
     * @param start 开始值
     * @param end 结束值
     * @return
     */
    public static int[] getRangRandom(int start, int end) {
        return getRangRandom(start, end, end - start + 1);
    }

    /**
     * 返回指定范围指定个数的不重复随机数。
     * 
     * @param start
     * @param end
     * @param num
     * @return
     */
    public static int[] getRangRandom(int start, int end, int num) {

        int length = end - start + 1;
        // 参数不合法
        if (length < 1 || num > length) {
            return null;
        } else {
            int[] numbers = new int[length];
            int[] result = new int[num];
            // 循环赋初始值
            for (int i = 0; i < length; i++) {
                numbers[i] = i + start;
            }
            Random random = new Random();
            // 取randomMax次数
            for (int i = 0; i < num; i++) {
                // 随机获取取数的位置
                int m = random.nextInt(length - i) + i;
                result[i] = numbers[m];
                // 交换位置
                int temp = numbers[m];
                numbers[m] = numbers[i];
                numbers[i] = temp;
            }
            return result;
        }
    }

    /*
     * 生成6位随机数验证码
     */
    public static String code() {
        Set<Integer> set = getRandomNumber();
        Iterator<Integer> iterator = set.iterator();
        String temp = "";
        while (iterator.hasNext()) {
            temp += iterator.next();
        }
        return temp;
    }

    public static Set<Integer> getRandomNumber() {
        Set<Integer> set = new LinkedHashSet<Integer>();
        Random random = new Random();
        while (set.size() < 6) {
            set.add(random.nextInt(10));
        }
        return set;
    }
    
    public static String[] chars = new String[] { "a", "b", "c", "d", "e", "f",
            "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s",
            "t", "u", "v", "w", "x", "y", "z", "0", "1", "2", "3", "4", "5",
            "6", "7", "8", "9", "A", "B", "C", "D", "E", "F", "G", "H", "I",
            "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V",
            "W", "X", "Y", "Z" };


    public static String getShortUUID(int num) {
        StringBuffer shortBuffer = new StringBuffer();
        String uuid = UUID.randomUUID().toString().replace("-", "");
        for (int i = 0; i < num; i++) {
            String str = uuid.substring(i * 4, i * 4 + 4);
            int x = Integer.parseInt(str, 16);
            shortBuffer.append(chars[x % 0x3E]);
        }
        return shortBuffer.toString();
    }
    
}