随机生成任意长度字符串

public static String getRandomString(int length){
            //定义一个字符串（A-Z，a-z，0-9）即62位；
            String str="zxcvbnmlkjhgfdsaqwertyuiopQWERTYUIOPASDFGHJKLZXCVBNM1234567890";
            //由Random生成随机数
            Random random=new Random();
            StringBuffer sb=new StringBuffer();
            //长度为几就循环几次
            for(int i=0; i