RandomUtils.java

package com.mlongbo.jfinal.common.utils;

import java.util.Random;
import java.util.UUID;

/**
 * @author malongbo
 */
public final class RandomUtils {

    /**
     * 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 = ("0123456789abcdefghijklmnopqrstuvwxyz" +
            "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ").toCharArray();


    /**
     * 根据指定长度随机生成小写字母
     * @param length 长度
     * @return 指定长度的随机小写字母字符串
     */
    public static String randomLowerWords(int length) {
        /*
           0~9的ASCII为48~57
           A~Z的ASCII为65~90
           a~z的ASCII为97~122
         */
        StringBuilder sb = new StringBuilder();
        Random randData = new Random();

        int data = 0;
        for(int i = 0; i < length; i++)
        {
            data=randData.nextInt(26)+97;//保证只会产生97~122之间的整数
            sb.append((char)data);
        }
        return sb.toString();
    }

    /**
     * 根据指定长度随机生成大写字母
     * @param length 长度
     * @return 指定长度的随机大写字母字符串
     */
    public static String randomUpperWords(int length) {
        /*
           0~9的ASCII为48~57
           A~Z的ASCII为65~90
           a~z的ASCII为97~122
         */
        StringBuilder sb = new StringBuilder();
        Random randData = new Random();

        int data = 0;
        for(int i = 0; i < length; i++)
        {
            data=randData.nextInt(26)+65;//保证只会产生97~122之间的整数
            sb.append((char)data);
        }
        return sb.toString();
    }

    /**
     * 根据指定长度随机生成数字
     * @param length 长度
     * @return 指定长度的随机数字
     */
    public static String randomNumbers(int length) {
        /*
           0~9的ASCII为48~57
           A~Z的ASCII为65~90
           a~z的ASCII为97~122
         */
        StringBuilder sb = new StringBuilder();
        Random randData = new Random();

        int data = 0;
        for(int i = 0; i < length; i++)
        {
            data=randData.nextInt(10);//仅仅会生成0~9
            sb.append(data);
        }
        return sb.toString();
    }

    /**
     * 生成32位UUID字符，去除字符'-'
     * @return 32位随机UUID字符串
     */
    public static String randomCustomUUID() {
        UUID uuid = UUID.randomUUID();
        String uuidStr = uuid.toString();

        return uuidStr.replaceAll("-","");
    }

    /**
     * 生成36位UUID字符
     * @return 36未随机UUID字符串
     */
    public static String randomUUID() {
        return UUID.randomUUID().toString();
    }

    /**
     * Returns a random String of numbers and letters (lower and upper case)
     * 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>
     * <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 String randomString(int length) {
        if (length < 1) {
            return null;
        }
        // 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[new Random().nextInt(71)];
        }
        return new String(randBuffer);
    }

}