java生成随机字符串

package com.suncco.wiley;

import java.util.Random;

public class GenerateAlphanum {

/**
* 方法一
*生成指定长度的字母数字组合字符串
*/
public static String getAlphanumString(int length) {
Random random = new Random();
StringBuffer buf = new StringBuffer();
String charStr = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
int charLength = charStr.length();
for (int i = 0; i < length; i++) {
int index = random.nextInt(charLength);
buf.append(charStr.charAt(index));
}
return buf.toString();
}
/**
* 方法二
*生成指定长度的字母数字组合字符串
*/
public static String getAlphanumString_(int length) {
StringBuffer buf = new StringBuffer();
Random random = new Random();
for (int i = 0; i < length; i++) {
String charOrNum = random.nextInt(2) % 2 == 0 ? "char" : "num"; // 输出字母还是数字
if ("char".equalsIgnoreCase(charOrNum)) {
// 字符串
int choice = random.nextInt(2) % 2 == 0 ? 65 : 97; // 取得大写字母还是小写字母
buf.append((char) (choice + random.nextInt(26)));
} else if ("num".equalsIgnoreCase(charOrNum)) {
// 数字
buf.append(String.valueOf(random.nextInt(10)));
}
}
return buf.toString();
}
/**
* 方法三
*生成指定长度的字母数字组合字符串
*/
public static String _getAlphanumString(int length) {
StringBuffer buf = new StringBuffer();
for (int i = 0; i < length; i++) {
// 输出字母还是数字
String charOrNum = Math.round(Math.random()) % 2 == 0 ? "char"
: "num";
if ("char".equalsIgnoreCase(charOrNum)) {
// 字符串
int choice = Math.round(Math.random()) % 2 == 0 ? 65 : 97; // 取得大写字母还是小写字母
buf.append((char) (choice + Math.round(Math.random() * 25)));
} else if ("num".equalsIgnoreCase(charOrNum)) {
// 数字
buf.append(String.valueOf(Math.round(Math.random() * 9)));
}
}
return buf.toString();
}

/**
* 方法四
* 一段生成指定范围的随机整数代码
* example：生成3-8之间的随机整数，直接调用 getSpecifyNum(3,8) 即返回大于等于3且小于等于8的整数。
*/
public static int getSpecifyNum(int min, int max) {
Random random = new Random();
return random.nextInt(max) % (max - min + 1) + min;
}

public static void main(String[] args) {
System.out.println(getAlphanumString(4));
System.out.println(getAlphanumString_(5));
System.out.println(_getAlphanumString(6));
System.out.println(getSpecifyNum(3,8));
}
}