工具类（自定义常用工具类）

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

public class DemoClass4Util {
    public static void main(String[] args) {
        String str24 = null;
        String str25 = "";
        String str26 = "  ";
        String str27 = "Frank";

        System.out.println(StringUtil.isEmpty(str24)); //true
        System.out.println(StringUtil.isEmpty(str25)); //true
        System.out.println(StringUtil.isEmpty(str26)); //true
        System.out.println(StringUtil.isEmpty(str27)); //false

        System.out.println("--------------");

        System.out.println(StringUtil.StringRandom());
        System.out.println(StringUtil.StringRandom("1234dkuewifjsk&*&^&", 50));
    }
}

//字符串工具类
class StringUtil{
    //判断是否为空
    public static boolean isEmpty(String str){
       /* if(str == null)
            return true;
        if("".equals(str))
            return true;
        if("".equals(str.trim()))
            return true;*/

        //整理代码
        if(str == null || "".equals(str.trim())){
            return true;
        }
        return false;
    }

    //生成随机字符串
    public static String StringRandom(){
        return UUID.randomUUID().toString().replace("-", "");
    }

    public static  String StringRandom(String fromStr, int len){
        if (len < 1) {
            return "";
        }else {
            char[] charArray = fromStr.toCharArray();
            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < len; i++) {
                Random random = new Random();
                //nextInt 随机获取下标
                int index = random.nextInt(charArray.length);
                char c = charArray[index];
                sb.append(c);
            }
            return sb.toString();
        }
    }
}