php生成唯一的串

1.方法一：

<?php
    md5(uniqid('aa',true));
?>

2.方法2：

//生成16位的串
$randLength=6;

$chars='abcdefghijklmnopqrstuvwxyz';

$len=strlen($chars);

$randStr='';

for ($i=0;$i<$randLength;$i++){

   $randStr.=$chars[rand(0,$len-1)];

}

$tokenvalue=$randStr.time();

 3.方法3:

$str = str_shuffle('abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890');
$str = $str.uniqid();
return md5($str);