Java随机密码生成器，Java随机生成长度不少于6的指定长度的密码，且这个字符串必须包含大小写字母、数字和特殊字符，四种的任意三种

import java.util.Random;

public class RandomPassword {
public static void main(String[] args) {

String password = getRandomPassword(8);
System.out.println(password);
}
//获取验证过的随机密码
public static String getRandomPassword(int len) {
String result = null;
/*if(len >= 6) {
for(result = makeRandomPassword(len);len >= 6;result = makeRandomPassword(len)){
if (result.matches(".*[a-z]{1,}.*") && result.matches(".*[A-Z]{1,}.*") && result.matches(".*\\d{1,}.*") && result.matches(".*[~!@#$%^&*\\.?]{1,}.*")) {
return result;
} 
}
}*/
while(len>=6){
result = makeRandomPassword(len);
if (result.matches(".*[a-z]{1,}.*") && result.matches(".*[A-Z]{1,}.*") && result.matches(".*\\d{1,}.*") && result.matches(".*[~!@#$%^&*\\.?]{1,}.*")) {
return result;
} 
result = makeRandomPassword(len);
}
return "长度不得少于6位!";
}
//随机密码生成
public static String makeRandomPassword(int len){
char charr[] = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890~!@#$%^&*.?".toCharArray();
//System.out.println("字符数组长度:" + charr.length);//可以看到调用此方法多少次
StringBuilder sb = new StringBuilder();
Random r = new Random();
for (int x = 0; x < len; ++x) {
sb.append(charr[r.nextInt(charr.length)]);
}
return sb.toString();
}

}