随机生成指定位数的0-9a-zA-Z字符串

import java.util.Random;

/**
 * 随机生成指定位数的0-9a-zA-Z字符串
 */
public class RandomStrTest {
    public static void main(String[] args) {
        System.out.println(getRandomStr(6));
        System.out.println(getRandomStr2(6));
    }


    private static String getRandomStr(int length){
        StringBuilder sb = new StringBuilder(length);
        for(int i = 0; i < length; i++){
            char c = getRandomChar();
            sb.append(c);
        }
        return sb.toString();
    }

    /**
     * 0-9  10 48-57
     * A-Z  26 65-90
     * a-z 26 97-122
     * 共62个
     * @return
     */
    private static char getRandomChar() {
        int ran = new Random().nextInt(62);//0-61
        //0-9
        if(ran < 10){
            return (char)(ran + 48);
        }
        //A-Z
        if(ran > 35){
            return (char)(ran + 61);
        }
        //a-z
        return (char)(ran + 55);
    }

    //===========================
    private static final char[] ary = {'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',
            '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'};

    private static String getRandomStr2(int length){
        StringBuilder sb = new StringBuilder(length);
        for(int i = 0; i < length; i++){
            char c = ary[new Random().nextInt(62)];
            sb.append(c);
        }
        return sb.toString();
    }
}