Java生成固定长度的随机字符串(以大小写字母和数字)

package org.jimmy.autosearch2019.test;

import java.util.ArrayList;
import java.util.Random;

/**
 * @author ラピスラズリ(Dawn)
 * @date 2019年5月30日 下午3:18:48
 * @detail 随机生成固定长度的字符串
 */
public class TestRandom2019053001 {

    public static ArrayList<String> strList = new ArrayList<String>();
    public static Random random = new Random();
    public static final int RANDOM_LENGTH1 = 256;
    public static final int RANDOM_LENGTH2 = 512;
    public static final int RANDOM_LENGTH3 = 1024;

    static {
        init();
    }

    public static void main(String[] args) {
        String randomStr = generateRandomStr(RANDOM_LENGTH1);
        System.out.println(RANDOM_LENGTH1 + "位随机数:" + randomStr);
        randomStr = generateRandomStr(RANDOM_LENGTH2);
        System.out.println(RANDOM_LENGTH2 + "位随机数:" + randomStr);
        randomStr = generateRandomStr(RANDOM_LENGTH3);
        System.out.println(RANDOM_LENGTH3 + "位随机数:" + randomStr);
    }

    public static String generateRandomStr(int length) {
        StringBuffer sb = new StringBuffer();
        for(int i = 0; i < length; i++) {
            int size = strList.size();
            String randomStr = strList.get(random.nextInt(size));
            sb.append(randomStr);
        }
        return sb.toString();
    }

    public static void init() {
        int begin = 97;
        //生成小写字母,并加入集合
        for(int i = begin; i < begin + 26; i++) {
            strList.add((char)i + "");
        }
        //生成大写字母,并加入集合
        begin = 65;
        for(int i = begin; i < begin + 26; i++) {
            strList.add((char)i + "");
        }
        //将0-9的数字加入集合
        for(int i = 0; i < 10; i++) {
            strList.add(i + "");
        }
    }

}

运行后效果:

256位随机数:qZP66hBKD2qZUNNw0seH2auRjw7wvtVAUAlV6Ze5jZXzL8H6MXSKSKcA3a5ae116DhMLD0jXlbNQp1YlRpDIpijbn9EtqPlWsIbvlrE1fZtnY8K88N6uhOYsCZc44A064arq0bK4tkCvVcXLPTyGeHJkBfujOrQfpkydRGTY1cGVSUgdVhrtyDUjBpNf393WRygZKSDUy704B2hzXWw7lTRImD5Y1evtXmglo4xmJn7XogvlsnenKlNtnZhfIz42
512位随机数: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
1024位随机数: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